1<?xml version="1.0" encoding="utf-8"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" 3"http://www.w3.org/TR/html4/loose.dtd"> 4<html> 5<head> 6<meta http-equiv=Content-Type content="text/html; charset=utf8"> 7<title>Acme: A User Interface for Programmers</title> 8</meta> 9</head> 10<body> 11<p style="margin-top: 0; margin-bottom: 0.50in"></p> 12<p style="margin-top: 0; margin-bottom: 0.21in"></p> 13 14<p style="line-height: 1.4em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: center;"> 15<span style="font-size: 12pt"><b>Acme: A User Interface for Programmers</b></span></p> 16<p style="margin-top: 0; margin-bottom: 0.21in"></p> 17 18<p style="margin-top: 0; margin-bottom: 0.17in"></p> 19<p style="line-height: 1.4em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: center;"> 20<span style="font-size: 10pt"><i></i></span><span style="font-size: 10pt"><i>Rob Pike</i></span><span style="font-size: 10pt"><i></i></span></p> 21<p style="line-height: 1.4em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: center;"> 22<span style="font-size: 10pt"><i></i></span><span style="font-size: 10pt"><i>rob@plan9.bell-labs.com</i></span><span style="font-size: 10pt"><i></i></span></p> 23<p style="margin-top: 0; margin-bottom: 0.17in"></p> 24 25<p style="margin-top: 0; margin-bottom: 0.08in"></p> 26<p style="margin-top: 0; margin-bottom: 0.33in"></p> 27<p style="line-height: 1.4em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: center;"> 28<span style="font-size: 10pt"><i>ABSTRACT</i></span></p> 29<p style="margin-top: 0; margin-bottom: 0.19in"></p> 30<p style="margin-top: 0; margin-bottom: 0.17in"></p> 31 32<p style="margin-top: 0; margin-bottom: 0.17in"></p> 33 34<p style="margin-top: 0; margin-bottom: 0.17in"></p> 35 36<p style="line-height: 1.2em; margin-left: 1.50in; text-indent: 0.00in; margin-right: 1.50in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 37<span style="font-size: 10pt">A hybrid of window system, shell, and editor, Acme gives text-oriented 38applications a clean, expressive, and consistent style of interaction. 39Traditional window systems support interactive client programs and offer libraries of 40pre-defined operations such as pop-up menus 41and buttons to promote a consistent 42user interface among the clients. 43Acme instead provides its clients with a fixed user interface and 44simple conventions to encourage its uniform use. 45Clients access the facilities of Acme through a file system interface; 46Acme is in part a file server that exports device-like files that may be 47manipulated to access and control the contents of its windows. 48Written in a concurrent programming language, 49Acme is structured as a set of communicating processes that neatly subdivide 50the various aspects of its tasks: display management, input, file server, and so on. 51</span><span style="font-size: 10pt"></span><span style="font-size: 10pt"></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 52<p style="line-height: 1.2em; margin-left: 1.50in; text-indent: 0.35in; margin-right: 1.50in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 53<span style="font-size: 10pt">Acme attaches distinct functions to the three mouse buttons: 54the left selects text; 55the middle executes textual commands; 56and the right combines context search and file opening 57functions to integrate the various applications and files in 58the system. 59</span><span style="font-size: 10pt"></span><span style="font-size: 10pt"></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 60<p style="line-height: 1.2em; margin-left: 1.50in; text-indent: 0.35in; margin-right: 1.50in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 61<span style="font-size: 10pt">Acme works well enough to have developed 62a community that uses it exclusively. 63Although Acme discourages the traditional style of interaction 64based on typescript windows—teletypes—its 65users find Acme’s other services render 66typescripts obsolete. 67</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p> 68 69<p style="margin-top: 0; margin-bottom: 0.17in"></p> 70<p style="margin-top: 0; margin-bottom: 0.17in"></p> 71<p style="margin-top: 0; margin-bottom: 0.50in"></p> 72<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 73<span style="font-size: 10pt"><b>History and motivation 74</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 75<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 76<span style="font-size: 10pt">The usual typescript style of interaction with 77Unix and its relatives is an old one. 78The typescript—an intermingling of textual commands and their 79output—originates with the scrolls of paper on teletypes. 80The advent of windowed terminals has given each user what 81amounts to an array of teletypes, a limited and unimaginative 82use of the powers of bitmap displays and mice. 83Systems like the Macintosh 84that do involve the mouse as an integral part of the interaction 85are geared towards general users, not experts, and certainly 86not programmers. 87Software developers, at least on time-sharing systems, have been left behind. 88</span></p><center><table width=60% cellspacing=0 cellpadding=0 border=0><tr height=1> <td width=1 bgcolor=#000000 /> <td width=10 bgcolor=#000000 /> <td bgcolor=#000000 /> <td width=10 bgcolor=#000000 /> <td width=1 bgcolor=#000000 /></tr><tr height=10> <td width=1 bgcolor=#000000 /> <td width=10 /> <td /> <td width=10 /> <td width=1 bgcolor=#000000 /></tr> 89<tr> 90<td width=1 bgcolor=#000000 /><td width=10 /><td> 91<center><a href="acme.fig1.gif"><img src="acme.fig1.gif" /></a></center> 92<p style="line-height: 1.2em; text-indent: 0.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 93<span style="font-size: 10pt">Figure 1. A small Acme screen—normally it runs on a larger display—demonstrating 94some of the details discussed in the text. 95The right column contains some guide files, 96a mailbox presented by Acme’s mail program, 97the columnated display of files in Acme’s own source directory, 98a couple of windows from the OED browser, 99a debugger window, 100and an error window showing diagnostics from a compilation. 101The left column holds a couple of source files 102(</span><span style="font-size: 10pt"><tt>dat.h</tt></span><span style="font-size: 10pt"> 103and 104</span><span style="font-size: 10pt"><tt>acme.l</tt></span><span style="font-size: 10pt">), 105another debugger window displaying a stack trace, 106and a third source file 107(</span><span style="font-size: 10pt"><tt>time.l</tt></span><span style="font-size: 10pt">). 108</span><span style="font-size: 10pt"><tt>Time.l</tt></span><span style="font-size: 10pt"> 109was opened from the debugger by clicking the right mouse button 110on a line in the stack window; 111the mouse cursor landed on the offending line of 112</span><span style="font-size: 10pt"><tt>acme.l</tt></span><span style="font-size: 10pt"> 113after a click on the compiler message. 114</span></p></td> 115<td width=10 /><td width=1 bgcolor=#000000 /> 116</tr> 117<tr height=10><td width=1 bgcolor=#000000 /> <td width=10 /><td /><td width=10 /> <td width=1 bgcolor=#000000 /></tr><tr height=1> <td width=1 bgcolor=#000000 /> <td width=10 bgcolor=#000000 /> <td bgcolor=#000000 /> <td width=10 bgcolor=#000000 /> <td width=1 bgcolor=#000000 /></tr> 118</table></center> 119<p style="margin-top: 0; margin-bottom: 0.05in"></p> 120<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 121<span style="font-size: 10pt">Some programs have mouse-based editing of 122text files and typescripts; 123ones I have built include 124the window systems 125</span><span style="font-size: 10pt"><tt>mux</tt></span><span style="font-size: 10pt"> 126[Pike88] 127and 128</span><span style="font-size: 10pt"><tt>8½</tt></span><span style="font-size: 10pt"> 129[Pike91] 130and the text editor 131Sam [Pike87]. 132These have put the programmer’s mouse to some productive work, 133but not wholeheartedly. Even experienced users of these programs 134often retype text that could be grabbed with the mouse, 135partly because the menu-driven interface is imperfect 136and partly because the various pieces are not well enough integrated. 137</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 138<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 139<span style="font-size: 10pt">Other programs—EMACS [Stal93] is the prime example—offer a high 140degree of integration but with a user interface built around the 141ideas of cursor-addressed terminals that date from the 1970’s. 142They are still keyboard-intensive and 143dauntingly complex. 144</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 145<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 146<span style="font-size: 10pt">The most ambitious attempt to face these issues was the Cedar 147system, developed at Xerox [Swei86]. 148It combined a new programming language, compilers, 149window system, even microcode—a complete system—to 150construct a productive, highly 151integrated and interactive environment 152for experienced users of compiled languages. 153Although successful internally, the system was so large 154and so tied to specific hardware that it never fledged. 155</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 156<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 157<span style="font-size: 10pt">Cedar was, however, the major inspiration for Oberon [Wirt89], 158a system of similar scope but much smaller scale. 159Through careful selection of Cedar’s ideas, Oberon shows 160that its lessons can be applied to a small, coherent system 161that can run efficiently on modest hardware. 162In fact, Oberon probably 163errs too far towards simplicity: a single-process system 164with weak networking, it seems an architectural throwback. 165</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 166<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 167<span style="font-size: 10pt">Acme is a new program, 168a combined window system, editor, and shell, 169that applies 170some of the ideas distilled by Oberon. 171Where Oberon uses objects and modules within a programming language (also called Oberon), 172Acme uses files and commands within an existing operating system (Plan 9). 173Unlike Oberon, Acme does not yet have support for graphical output, just text. 174At least for now, the work on Acme has concentrated on 175producing the smoothest user interface possible for a programmer 176at work. 177</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 178<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 179<span style="font-size: 10pt">The rest of this paper describes Acme’s interface, 180explains how programs can access it, 181compares it to existing systems, 182and finally presents some unusual aspects of its implementation. 183</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p> 184<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 185<span style="font-size: 10pt"><b>User interface 186</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 187<center><table width=60% cellspacing=0 cellpadding=0 border=0><tr height=1> <td width=1 bgcolor=#000000 /> <td width=10 bgcolor=#000000 /> <td bgcolor=#000000 /> <td width=10 bgcolor=#000000 /> <td width=1 bgcolor=#000000 /></tr><tr height=10> <td width=1 bgcolor=#000000 /> <td width=10 /> <td /> <td width=10 /> <td width=1 bgcolor=#000000 /></tr> 188<tr> 189<td width=1 bgcolor=#000000 /><td width=10 /><td> 190<center><a href="acme.fig2.gif"><img src="acme.fig2.gif" /></a></center> 191<p style="line-height: 1.2em; text-indent: 0.35in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 192<span style="font-size: 10pt">Figure 2. An Acme window showing a section of code. 193The upper line of text is the tag containing the file name, 194relevant commands, and a scratch area (right of the vertical bar); 195the lower portion of the window is the 196body, or contents, of the file. 197Here the scratch area contains a command for the middle button 198(</span><span style="font-size: 10pt"><tt>mk</tt></span><span style="font-size: 10pt">) 199and a word to search for with the right button 200(</span><span style="font-size: 10pt"><tt>cxfidalloc</tt></span><span style="font-size: 10pt">). 201The user has just 202clicked the right button on 203</span><span style="font-size: 10pt"><tt>cxfidalloc</tt></span><span style="font-size: 10pt"> 204and Acme has searched for the word, highlighted it, 205and moved the mouse cursor there. The file has been modified: 206the center of the layout box is black and the command 207</span><span style="font-size: 10pt"><tt>Put</tt></span><span style="font-size: 10pt"> 208appears in the tag. 209</span></p></td> 210<td width=10 /><td width=1 bgcolor=#000000 /> 211</tr> 212<tr height=10><td width=1 bgcolor=#000000 /> <td width=10 /><td /><td width=10 /> <td width=1 bgcolor=#000000 /></tr><tr height=1> <td width=1 bgcolor=#000000 /> <td width=10 bgcolor=#000000 /> <td bgcolor=#000000 /> <td width=10 bgcolor=#000000 /> <td width=1 bgcolor=#000000 /></tr> 213</table></center> 214<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 215<span style="font-size: 10pt">Acme windows are arrayed in columns (Figure 1) and are used more 216dynamically than in an environment like X Windows or 217</span><span style="font-size: 10pt"><tt>8½</tt></span><span style="font-size: 10pt"> 218[Sche86, Pike91]. 219The system frequently creates them automatically and the user 220can order a new one with a single mouse button click. 221The initial placement of a new window is determined 222automatically, but the user may move an existing window anywhere 223by clicking or dragging a 224</span><span style="font-size: 10pt"><i>layout box</i></span><span style="font-size: 10pt"> 225in the upper left corner of 226the window. 227</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 228<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 229<span style="font-size: 10pt">Acme windows have two parts: a 230</span><span style="font-size: 10pt"><i>tag</i></span><span style="font-size: 10pt"> 231holding a single line of text, 232above a 233</span><span style="font-size: 10pt"><i>body</i></span><span style="font-size: 10pt"> 234holding zero or more lines (Figure 2). 235The body typically contains an image of a file being edited 236or the editable output of a 237program, analogous to an 238EMACS shell 239window. The tag contains 240the name of the window 241(usually the name of the associated 242file or directory), some built-in commands, and a scratch area to hold arbitrary text. 243If a window represents a directory, the name in the tag ends with 244a slash and the body contains a list of the names of the files 245in the directory. 246Finally, each non-empty body holds a scroll bar at the left of the text. 247</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 248<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 249<span style="font-size: 10pt">Each column of windows also has a layout box and a tag. 250The tag has no special meaning, although Acme pre-loads it with a few 251built-in commands. 252There is also a tag across the whole display, also loaded with 253helpful commands and a list of active processes started 254by Acme. 255</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 256<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 257<span style="font-size: 10pt">Typing with the keyboard and selecting with the left button are as in 258many other systems, including the Macintosh, 259</span><span style="font-size: 10pt"><tt>8½</tt></span><span style="font-size: 10pt">, 260and Sam. 261The middle and right buttons are used, somewhat like the left button, 262to ‘sweep’ text, but the indicated text is treated in a way 263that depends on the text’s location—</span><span style="font-size: 10pt"><i>context</i></span><span style="font-size: 10pt">—as well as its content. 264This context, based on the directory of the file containing the text, 265is a central component of Acme’s style of interaction. 266</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 267<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 268<span style="font-size: 10pt">Acme has no single notion of ‘current directory’. 269Instead, every command, file name, 270action, and so on is interpreted or executed in the directory named by the 271tag of the window containing the command. For example, the string 272</span><span style="font-size: 10pt"><tt>mammals</tt></span><span style="font-size: 10pt"> 273in a window labeled 274</span><span style="font-size: 10pt"><tt>/lib/</tt></span><span style="font-size: 10pt"> 275or 276</span><span style="font-size: 10pt"><tt>/lib/insects</tt></span><span style="font-size: 10pt"> 277will be interpreted as the file name 278</span><span style="font-size: 10pt"><tt>/lib/mammals</tt></span><span style="font-size: 10pt"> 279if such a file exists. 280</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 281<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 282<span style="font-size: 10pt">Throughout Acme, the middle mouse button is used to execute commands 283and the right mouse button is used to locate and select files and text. 284Even when there are no true files on which to operate—for example 285when editing mail messages—Acme and its applications use 286consistent extensions of these basic functions. 287This idea is as vital to Acme as icons are to the Macintosh. 288</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 289<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 290<span style="font-size: 10pt">The middle button executes commands: text swept with the button 291pressed is underlined; when the button is released, the underline is 292removed and the indicated text is executed. 293A modest number of commands are recognized as built-ins: words like 294</span><span style="font-size: 10pt"><tt>Cut</tt></span><span style="font-size: 10pt">, 295</span><span style="font-size: 10pt"><tt>Paste</tt></span><span style="font-size: 10pt">, 296and 297</span><span style="font-size: 10pt"><tt>New</tt></span><span style="font-size: 10pt"> 298name 299functions performed directly by Acme. 300These words often appear in tags to make them always available, 301but the tags are not menus: any text anywhere in Acme may be a command. 302For example, in the tag or body of any window one may type 303</span><span style="font-size: 10pt"><tt>Cut</tt></span><span style="font-size: 10pt">, 304select it with the left button, use the middle button to execute it, 305and watch it disappear again. 306</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 307<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 308<span style="font-size: 10pt">If the middle button indicates a command that is not recognized as a built-in, 309it is executed in the directory 310named by the tag of the window holding the text. 311Also, the file to be executed is searched for first in that directory. 312Standard input is connected to 313</span><span style="font-size: 10pt"><tt>/dev/null</tt></span><span style="font-size: 10pt">, 314but standard and error outputs are connected to an Acme window, 315created if needed, called 316</span><span style="font-size: 10pt"><i>dir</i></span><span style="font-size: 10pt"><tt>/+Errors</tt></span><span style="font-size: 10pt"> where 317</span><span style="font-size: 10pt"><i>dir</i></span><span style="font-size: 10pt"> 318is the directory of the window. 319(Programs that need interactive input use a different interface, described below.) 320A typical use of this is to type 321</span><span style="font-size: 10pt"><tt>mk</tt></span><span style="font-size: 10pt"> 322(Plan 9’s 323</span><span style="font-size: 10pt"><tt>make</tt></span><span style="font-size: 10pt">) 324in the scratch area in the tag of a C source window, say 325</span><span style="font-size: 10pt"><tt>/sys/src/cmd/sam/regexp.c</tt></span><span style="font-size: 10pt">, 326and execute it. 327Output, including compiler errors, appears in the window labeled 328</span><span style="font-size: 10pt"><tt>/sys/src/cmd/sam/+Errors</tt></span><span style="font-size: 10pt">, 329so file names in the output are associated with the windows and directory 330holding the source. 331The 332</span><span style="font-size: 10pt"><tt>mk</tt></span><span style="font-size: 10pt"> 333command remains in the tag, serving as a sort of menu item for the associated 334window. 335</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 336<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 337<span style="font-size: 10pt">Like the middle button, the right button is used to indicate text by sweeping it out. 338The indicated text is not a command, however, but the argument of a generalized 339search operator. 340If the text, perhaps after appending it to the directory of the window containing it, 341is the name of an existing file, Acme creates a new window to hold the file 342and reads it in. It then moves the mouse cursor to that window. If the file is 343already loaded into Acme, the mouse motion happens but no new window is made. 344For example, indicating the string 345</span><span style="font-size: 10pt"><tt>sam.h</tt></span><span style="font-size: 10pt"> 346in 347</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p> 348<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 349<span style="font-size: 9pt"><tt>#include "sam.h"</tt></span></p> 350<p style="margin-top: 0; margin-bottom: 0.17in"></p> 351 352<p style="margin-top: 0; margin-bottom: 0.08in"></p> 353<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 354<span style="font-size: 10pt">in a window on the file 355</span><span style="font-size: 10pt"><tt>/sys/src/cmd/sam/regexp.c</tt></span><span style="font-size: 10pt"> 356will open the file 357</span><span style="font-size: 10pt"><tt>/sys/src/cmd/sam/sam.h</tt></span><span style="font-size: 10pt">. 358</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 359<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 360<span style="font-size: 10pt">If the file name is followed immediately by a colon and a legal address in 361Sam notation (for example a line number or a regular expression delimited in 362slashes or a comma-separated compound of such addresses), Acme highlights 363the target of that address in the file and places the mouse there. One may jump to 364line 27 of 365</span><span style="font-size: 10pt"><tt>dat.h</tt></span><span style="font-size: 10pt"> 366by indicating with the right button the text 367</span><span style="font-size: 10pt"><tt>dat.h:27</tt></span><span style="font-size: 10pt">. 368If the file is not already open, Acme loads it. 369If the file name is null, for example if the indicated string is 370</span><span style="font-size: 10pt"><tt>:/^main/</tt></span><span style="font-size: 10pt">, 371the file is assumed to be that of the window containing the string. 372Such strings, when typed and evaluated in the tag of a window, amount to 373context searches. 374</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 375<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 376<span style="font-size: 10pt">If the indicated text is not the name of an existing file, it is taken to be literal 377text and is searched for in the body of the window containing the text, highlighting 378the result as if it were the result of a context search. 379</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 380<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 381<span style="font-size: 10pt">For the rare occasion when a file name 382</span><span style="font-size: 10pt"><i>is</i></span><span style="font-size: 10pt"> 383just text to search for, it can be selected with the left button and used as the 384argument to a built-in 385</span><span style="font-size: 10pt"><tt>Look</tt></span><span style="font-size: 10pt"> 386command that always searches for literal text. 387</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p> 388<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 389<span style="font-size: 10pt"><b>Nuances and heuristics 390</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 391<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 392<span style="font-size: 10pt">A user interface should not only provide the necessary functions, it should also 393</span><span style="font-size: 10pt"><i>feel</i></span><span style="font-size: 10pt"> 394right. 395In fact, it should almost not be felt at all; when one notices a 396user interface, one is distracted from the job at hand [Pike88]. 397To approach this invisibility, some of Acme’s properties and features 398are there just to make the others easy to use. 399Many are based on a fundamental principle of good design: 400let the machine do the work. 401</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 402<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 403<span style="font-size: 10pt">Acme tries to avoid needless clicking and typing. 404There is no ‘click-to-type’, eliminating a button click. 405There are no pop-up or pull-down menus, eliminating the mouse action needed to 406make a menu appear. 407The overall design is intended to make text on the screen useful without 408copying or retyping; the ways in which this happens involve 409the combination of many aspects of the interface. 410</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 411<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 412<span style="font-size: 10pt">Acme tiles its windows and places them automatically 413to avoid asking the user to place and arrange them. 414For this policy to succeed, the automatic placement must behave well enough 415that the user is usually content with the location of a new window. 416The system will never get it right all the time, but in practice most 417windows are used at least for a while where Acme first places them. 418There have been several complete rewrites of the 419heuristics for placing a new window, 420and with each rewrite the system became 421noticeably more comfortable. The rules are as follows, although 422they are still subject to improvement. 423The window appears in the ‘active’ column, that most recently used for typing or 424selecting. 425Executing and searching do not affect the choice of active column, 426so windows of commands and such do not draw new windows towards them, 427but rather let them form near the targets of their actions. 428Output (error) windows always appear towards the right, away from 429edited text, which is typically kept towards the left. 430Within the column, several competing desires are balanced to decide where 431and how large the window should be: 432large blank spaces should be consumed; 433existing text should remain visible; 434existing large windows should be divided before small ones; 435and the window should appear near the one containing the action that caused 436its creation. 437</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 438<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 439<span style="font-size: 10pt">Acme binds some actions to chords of mouse buttons. 440These include 441</span><span style="font-size: 10pt"><tt>Cut</tt></span><span style="font-size: 10pt"> 442and 443</span><span style="font-size: 10pt"><tt>Paste</tt></span><span style="font-size: 10pt"> 444so these common operations can be done without 445moving the mouse. 446Another is a way to apply a command in one window to text (often a file name) 447in another, avoiding the actions needed to assemble the command textually. 448</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 449<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 450<span style="font-size: 10pt">Another way Acme avoids the need to move the mouse is instead to move the cursor 451to where it is likely to be used next. When a new window is made, Acme 452moves the cursor to the new window; in fact, to the selected text in that window. 453When the user deletes a newly made window, the cursor is 454returned to the point it was before the window was made, 455reducing the irritation of windows that pop up to report annoying errors. 456</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 457<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 458<span style="font-size: 10pt">When a window is moved, Acme moves the cursor to the layout box in 459its new place, to permit further adjustment without moving the mouse. 460For example, when a click of the left mouse button on the layout box grows 461the window, the cursor moves to the new location of the box so repeated clicks, 462without moving the mouse, continue to grow it. 463</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 464<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 465<span style="font-size: 10pt">Another form of assistance the system can offer is to supply precision in 466pointing the mouse. The best-known form of this is ‘double-clicking’ to 467select a word rather than carefully sweeping out the entire word. 468Acme provides this feature, using context to decide whether to select 469a word, line, quoted string, parenthesized expression, and so on. 470But Acme takes the idea much further by applying it to execution 471and searching. 472A 473</span><span style="font-size: 10pt"><i>single</i></span><span style="font-size: 10pt"> 474click, that is, a null selection, with either the middle or right buttons, 475is expanded automatically to indicate the appropriate text containing 476the click. What is appropriate depends on the context. 477</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 478<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 479<span style="font-size: 10pt">For example, to execute a single-word command 480such as 481</span><span style="font-size: 10pt"><tt>Cut</tt></span><span style="font-size: 10pt">, 482it is not necessary to sweep the entire word; just clicking the button once with 483the mouse pointing at the word is sufficient. ‘Word’ 484means the largest string of likely file name characters surrounding the location 485of the click: click on a file name, run that program. 486On the right button, the rules are more complicated because 487the target of the click might be a file name, file name with address, 488or just plain text. Acme examines the text near the click to find 489a likely file name; 490if it finds one, it checks that it names an existing file (in the directory named in the tag, if the name is relative) 491and if so, takes that as the result, after extending it with any address 492that may be present. If there is no file with that name, Acme 493just takes the largest alphanumeric string under the click. 494The effect is a natural overloading of the button to refer to plain text as 495well as file names. 496</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 497<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 498<span style="font-size: 10pt">First, though, if the click occurs over the left-button-selected text in the window, 499that text is taken to be what is selected. 500This makes it easy to skip through the occurrences of a string in a file: just click 501the right button 502on some occurrence of the text in the window (perhaps after typing it in the tag) 503and click once for each subsequent occurrence. It isn’t even necessary to move 504the mouse between clicks; Acme does that. 505To turn a complicated command into a sort of menu item, select it: 506thereafter, clicking the middle button on it will execute the full command. 507</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 508<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 509<span style="font-size: 10pt">As an extra feature, Acme recognizes file names in angle brackets 510</span><span style="font-size: 10pt"><tt><></tt></span><span style="font-size: 10pt"> 511as names of files in standard directories of include files, 512making it possible for instance to look at 513</span><span style="font-size: 10pt"><tt><stdio.h></tt></span><span style="font-size: 10pt"> 514with a single click. 515</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 516<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 517<span style="font-size: 10pt">Here’s an example to demonstrate how the actions and defaults work together. 518Assume 519</span><span style="font-size: 10pt"><tt>/sys/src/cmd/sam/regexp.c</tt></span><span style="font-size: 10pt"> 520is 521open and has been edited. We write it (execute 522</span><span style="font-size: 10pt"><tt>Put</tt></span><span style="font-size: 10pt"> 523in the tag; once the file is written, Acme removes the word from the tag) 524and type 525</span><span style="font-size: 10pt"><tt>mk</tt></span><span style="font-size: 10pt"> 526in the tag. We execute 527</span><span style="font-size: 10pt"><tt>mk</tt></span><span style="font-size: 10pt"> 528and get some errors, which appear in a new window labeled 529</span><span style="font-size: 10pt"><tt>/sys/src/cmd/sam/+Errors</tt></span><span style="font-size: 10pt">. 530The cursor moves automatically to that window. 531Say the error is 532</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p> 533<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 534<span style="font-size: 9pt"><tt>main.c:112: incompatible types on assignment to ‘pattern’</tt></span></p> 535<p style="margin-top: 0; margin-bottom: 0.17in"></p> 536 537<p style="margin-top: 0; margin-bottom: 0.08in"></p> 538<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 539<span style="font-size: 10pt">We move the mouse slightly and click the right button 540at the left of the error message; Acme 541makes a new window, reads 542</span><span style="font-size: 10pt"><tt>/sys/src/cmd/main.c</tt></span><span style="font-size: 10pt"> 543into it, selects line 112 544and places the mouse there, right on the offending line. 545</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p> 546<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 547<span style="font-size: 10pt"><b>Coupling to existing programs 548</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 549<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 550<span style="font-size: 10pt">Acme’s syntax for file names and addresses makes it easy for other programs 551to connect automatically to Acme’s capabilities. For example, the output of 552</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p> 553<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 554<span style="font-size: 9pt"><tt>grep -n variable *.[ch]</tt></span></p> 555<p style="margin-top: 0; margin-bottom: 0.17in"></p> 556 557<p style="margin-top: 0; margin-bottom: 0.08in"></p> 558<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 559<span style="font-size: 10pt">can be used to help Acme step through the occurrences of a variable in a program; 560every line of output is potentially a command to open a file. 561The file names need not be absolute, either: the output 562appears in a window labeled with the directory in which 563</span><span style="font-size: 10pt"><tt>grep</tt></span><span style="font-size: 10pt"> 564was run, from which Acme can derive the full path names. 565</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 566<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 567<span style="font-size: 10pt">When necessary, we have changed the output of some programs, 568such as compiler error messages, to match 569Acme’s syntax. 570Some might argue that it shouldn’t be necessary to change old programs, 571but sometimes programs need to be updated when systems change, 572and consistent output benefits people as well as programs. 573A historical example is the retrofitting of standard error output to the 574early Unix programs when pipes were invented. 575</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 576<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 577<span style="font-size: 10pt">Another change was to record full path names in 578the symbol table of executables, so line numbers reported by the debugger 579are absolute names that may be used directly by Acme; it’s not necessary 580to run the debugger in the source directory. (This aids debugging 581even without Acme.) 582</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 583<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 584<span style="font-size: 10pt">A related change was to add lines of the form 585</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p> 586<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 587<span style="font-size: 9pt"><tt>#pragma src "/sys/src/libregexp"</tt></span></p> 588<p style="margin-top: 0; margin-bottom: 0.17in"></p> 589 590<p style="margin-top: 0; margin-bottom: 0.08in"></p> 591<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 592<span style="font-size: 10pt">to header files; coupled with Acme’s ability to locate a header file, 593this provides a fast, keyboardless way to get the source associated with a library. 594</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 595<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 596<span style="font-size: 10pt">Finally, Acme directs the standard output of programs it runs to 597windows labeled by the directory in which the program is run. 598Acme’s splitting of the 599output into directory-labeled windows is a small feature that has a major effect: 600local file names printed by programs can be interpreted directly by Acme. 601By indirectly coupling the output of programs to the input, 602it also simplifies the management of software that occupies multiple 603directories. 604</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p> 605<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 606<span style="font-size: 10pt"><b>Coupling to new programs 607</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 608<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 609<span style="font-size: 10pt">Like many Plan 9 programs, 610Acme offers a programmable interface to 611other programs by acting as a file server. 612The best example of such a file server is the window system 613</span><span style="font-size: 10pt"><tt>8½</tt></span><span style="font-size: 10pt"> 614[Pike91], 615which exports files with names such as 616</span><span style="font-size: 10pt"><tt>screen</tt></span><span style="font-size: 10pt">, 617</span><span style="font-size: 10pt"><tt>cons</tt></span><span style="font-size: 10pt">, 618and 619</span><span style="font-size: 10pt"><tt>mouse</tt></span><span style="font-size: 10pt"> 620through which applications may access the I/O capabilities of the windows. 621</span><span style="font-size: 10pt"><tt>8½</tt></span><span style="font-size: 10pt"> 622provides a 623</span><span style="font-size: 10pt"><i>distinct</i></span><span style="font-size: 10pt"> 624set of files for each window and builds a private file name space 625for the clients running ‘in’ each window; 626clients in separate windows see distinct files with the same names 627(for example 628</span><span style="font-size: 10pt"><tt>/dev/mouse</tt></span><span style="font-size: 10pt">). 629Acme, like the process file system [PPTTW93], instead associates each 630window with a directory of files; the files of each window are visible 631to any application. 632This difference reflects a difference in how the systems are used: 633</span><span style="font-size: 10pt"><tt>8½</tt></span><span style="font-size: 10pt"> 634tells a client what keyboard and mouse activity has happened in its window; 635Acme tells a client what changes that activity wrought on any window it asks about. 636Putting it another way, 637</span><span style="font-size: 10pt"><tt>8½</tt></span><span style="font-size: 10pt"> 638enables the construction of interactive applications; 639Acme provides the interaction for applications. 640</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 641<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 642<span style="font-size: 10pt">The root of 643Acme’s file system is mounted using Plan 9 operations on the directory 644</span><span style="font-size: 10pt"><tt>/mnt/acme</tt></span><span style="font-size: 10pt">. 645In 646that root directory appears a directory for each window, numbered with the window’s identifier, 647analogous to a process identifier, for example 648</span><span style="font-size: 10pt"><tt>/mnt/acme/27</tt></span><span style="font-size: 10pt">. 649The window’s directory 650contains 6 files: 651</span><span style="font-size: 10pt"><tt>/mnt/acme/27/addr</tt></span><span style="font-size: 10pt">, 652</span><span style="font-size: 10pt"><tt>body</tt></span><span style="font-size: 10pt">, 653</span><span style="font-size: 10pt"><tt>ctl</tt></span><span style="font-size: 10pt">, 654</span><span style="font-size: 10pt"><tt>data</tt></span><span style="font-size: 10pt">, 655</span><span style="font-size: 10pt"><tt>event</tt></span><span style="font-size: 10pt">, 656and 657</span><span style="font-size: 10pt"><tt>tag</tt></span><span style="font-size: 10pt">. 658The 659</span><span style="font-size: 10pt"><tt>body</tt></span><span style="font-size: 10pt"> 660and 661</span><span style="font-size: 10pt"><tt>tag</tt></span><span style="font-size: 10pt"> 662files contain the text of the respective parts of the window; they may be 663read to recover the contents. Data written to these files is appended to the text; 664</span><span style="font-size: 10pt"><tt>seeks</tt></span><span style="font-size: 10pt"> 665are ignored. 666The 667</span><span style="font-size: 10pt"><tt>addr</tt></span><span style="font-size: 10pt"> 668and 669</span><span style="font-size: 10pt"><tt>data</tt></span><span style="font-size: 10pt"> 670files provide random access to the contents of the body. 671The 672</span><span style="font-size: 10pt"><tt>addr</tt></span><span style="font-size: 10pt"> 673file is written to set a character position within the body; the 674</span><span style="font-size: 10pt"><tt>data</tt></span><span style="font-size: 10pt"> 675file may then be read to recover the contents at that position, 676or written to change them. 677(The tag is assumed 678small and special-purpose enough not to need special treatment. 679Also, 680</span><span style="font-size: 10pt"><tt>addr</tt></span><span style="font-size: 10pt"> 681indexes by character position, which is not the same as byte offset 682in Plan 9’s multi-byte character set [Pike93]). 683The format accepted by the 684</span><span style="font-size: 10pt"><tt>addr</tt></span><span style="font-size: 10pt"> 685file is exactly the syntax of addresses within the user interface, 686permitting regular expressions, line numbers, and compound addresses 687to be specified. For example, to replace the contents of lines 3 through 7, 688write the text 689</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p> 690<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 691<span style="font-size: 9pt"><tt>3,7</tt></span></p> 692<p style="margin-top: 0; margin-bottom: 0.17in"></p> 693 694<p style="margin-top: 0; margin-bottom: 0.08in"></p> 695<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 696<span style="font-size: 10pt">to the 697</span><span style="font-size: 10pt"><tt>addr</tt></span><span style="font-size: 10pt"> 698file, then write the replacement text to the 699</span><span style="font-size: 10pt"><tt>data</tt></span><span style="font-size: 10pt"> 700file. A zero-length write deletes the addressed text; further writes extend the replacement. 701</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 702<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 703<span style="font-size: 10pt">The control file, 704</span><span style="font-size: 10pt"><tt>ctl</tt></span><span style="font-size: 10pt">, 705may be written with commands to effect actions on the window; for example 706the command 707</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p> 708<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 709<span style="font-size: 9pt"><tt>name /adm/users</tt></span></p> 710<p style="margin-top: 0; margin-bottom: 0.17in"></p> 711 712<p style="margin-top: 0; margin-bottom: 0.08in"></p> 713<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 714<span style="font-size: 10pt">sets the name in the tag of the window to 715</span><span style="font-size: 10pt"><tt>/adm/users</tt></span><span style="font-size: 10pt">. 716Other commands allow deleting the window, writing it to a file, and so on. 717Reading the 718</span><span style="font-size: 10pt"><tt>ctl</tt></span><span style="font-size: 10pt"> 719file recovers a fixed-format string containing 5 textual numbers—the window 720identifier, the number of characters in the tag, the number in the body, 721and some status information—followed by the text of the tag, up to a newline. 722</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 723<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 724<span style="font-size: 10pt">The last file, 725</span><span style="font-size: 10pt"><tt>event</tt></span><span style="font-size: 10pt">, 726is the most unusual. 727A program reading a window’s 728</span><span style="font-size: 10pt"><tt>event</tt></span><span style="font-size: 10pt"> 729file is notified of all changes to the text of the window, and 730is asked to interpret all middle- and right-button actions. 731The data passed to the program is fixed-format and reports 732the source of the action (keyboard, mouse, external program, etc.), 733its location (what was pointed at or modified), and its nature (change, 734search, execution, etc.). 735This message, for example, 736</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p> 737<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 738<span style="font-size: 9pt"><tt>MI15 19 0 4 time</tt></span></p> 739<p style="margin-top: 0; margin-bottom: 0.17in"></p> 740 741<p style="margin-top: 0; margin-bottom: 0.08in"></p> 742<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 743<span style="font-size: 10pt">reports that actions of the mouse 744(</span><span style="font-size: 10pt"><tt>M</tt></span><span style="font-size: 10pt">) 745inserted in the body (capital 746</span><span style="font-size: 10pt"><tt>I</tt></span><span style="font-size: 10pt">) 747the 4 characters of 748</span><span style="font-size: 10pt"><tt>time</tt></span><span style="font-size: 10pt"> 749at character positions 15 through 19; the zero is a flag word. 750Programs may apply their own interpretations of searching and 751execution, or may simply reflect the events back to Acme, 752by writing them back to the 753</span><span style="font-size: 10pt"><tt>event</tt></span><span style="font-size: 10pt"> 754file, to have the default interpretation applied. 755Some examples of these ideas in action are presented below. 756</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 757<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 758<span style="font-size: 10pt">Notice that changes to the window are reported 759after the fact; the program is told about them but is not required to act 760on them. Compare this to a more traditional interface in which a program 761is told, for example, that a character has been typed on the keyboard and 762must then display and interpret it. 763Acme’s style stems from the basic model of the system, in which any 764number of agents—the keyboard, mouse, external programs 765writing to 766</span><span style="font-size: 10pt"><tt>data</tt></span><span style="font-size: 10pt"> 767or 768</span><span style="font-size: 10pt"><tt>body</tt></span><span style="font-size: 10pt">, 769and so on—may 770change the contents of a window. 771The style is efficient: many programs are content 772to have Acme do most of the work and act only when the editing is completed. 773An example is the Acme mail program, which can ignore the changes 774made to a message being composed 775and just read its body when asked to send it. 776A disadvantage is that some traditional ways of working are impossible. 777For example, there is no way ‘to turn off echo’: characters appear on the 778screen and are read from there; no agent or buffer stands between 779the keyboard and the display. 780</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 781<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 782<span style="font-size: 10pt">There are a couple of other files made available by Acme in its root directory 783rather than in the directory of each window. 784The text file 785</span><span style="font-size: 10pt"><tt>/mnt/acme/index</tt></span><span style="font-size: 10pt"> 786holds a list of all window names and numerical identifiers, 787somewhat analogous to the output of the 788</span><span style="font-size: 10pt"><tt>ps</tt></span><span style="font-size: 10pt"> 789command for processes. 790The most important, though, is 791</span><span style="font-size: 10pt"><tt>/mnt/acme/new</tt></span><span style="font-size: 10pt">, 792a directory that makes new windows, similar to the 793</span><span style="font-size: 10pt"><tt>clone</tt></span><span style="font-size: 10pt"> 794directory in the Plan 9 network devices [Pres93]. 795The act of opening any file in 796</span><span style="font-size: 10pt"><tt>new</tt></span><span style="font-size: 10pt"> 797creates a new Acme window; thus the shell command 798</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p> 799<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 800<span style="font-size: 9pt"><tt>grep -n var *.c > /mnt/acme/new/body</tt></span></p> 801<p style="margin-top: 0; margin-bottom: 0.17in"></p> 802 803<p style="margin-top: 0; margin-bottom: 0.08in"></p> 804<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 805<span style="font-size: 10pt">places its output in the body of a fresh window. 806More sophisticated applications may open 807</span><span style="font-size: 10pt"><tt>new/ctl</tt></span><span style="font-size: 10pt">, 808read it to discover the new window’s identifier, and then 809open the window’s other files in the numbered directory. 810</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p> 811<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 812<span style="font-size: 10pt"><b>Acme-specific programs 813</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 814<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 815<span style="font-size: 10pt">Although Acme is in part an attempt to move beyond typescripts, 816they will probably always have utility. 817The first program written for Acme was therefore one 818to run a shell or other traditional interactive application 819in a window, the Acme analog of 820</span><span style="font-size: 10pt"><tt>xterm</tt></span><span style="font-size: 10pt">. 821This program, 822</span><span style="font-size: 10pt"><tt>win</tt></span><span style="font-size: 10pt">, 823has a simple structure: 824it acts as a two-way intermediary between Acme and the shell, 825cross-connecting the standard input and output of the shell to the 826text of the window. 827The style of interaction is modeled after 828</span><span style="font-size: 10pt"><tt>mux</tt></span><span style="font-size: 10pt"> 829[Pike88]: standard output is added to the window at the 830</span><span style="font-size: 10pt"><i>output point;</i></span><span style="font-size: 10pt"> 831text typed after the output point 832is made available on standard input when a newline is typed. 833After either of these actions, the output point is advanced. 834This is different from the working of a regular terminal, 835permitting cut-and-paste editing of an input line until the newline is typed. 836Arbitrary editing may be done to any text in the window. 837The implementation of 838</span><span style="font-size: 10pt"><tt>win</tt></span><span style="font-size: 10pt">, 839using the 840</span><span style="font-size: 10pt"><tt>event</tt></span><span style="font-size: 10pt">, 841</span><span style="font-size: 10pt"><tt>addr</tt></span><span style="font-size: 10pt">, 842and 843</span><span style="font-size: 10pt"><tt>data</tt></span><span style="font-size: 10pt"> 844files, is straightforward. 845</span><span style="font-size: 10pt"><tt>Win</tt></span><span style="font-size: 10pt"> 846needs no code for handling the keyboard and mouse; it just monitors the 847contents of the window. Nonetheless, it allows Acme’s full editing to be 848applied to shell commands. 849The division of labor between 850</span><span style="font-size: 10pt"><tt>win</tt></span><span style="font-size: 10pt"> 851and 852</span><span style="font-size: 10pt"><tt>Acme</tt></span><span style="font-size: 10pt"> 853contrasted with 854</span><span style="font-size: 10pt"><tt>xterm</tt></span><span style="font-size: 10pt"> 855and the X server demonstrates how much work Acme handles automatically. 856</span><span style="font-size: 10pt"><tt>Win</tt></span><span style="font-size: 10pt"> 857is implemented by a single source file 560 lines long and has no graphics code. 858</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 859<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 860<span style="font-size: 10pt"></span><span style="font-size: 10pt"><tt>Win</tt></span><span style="font-size: 10pt"> 861uses the middle and right buttons to connect itself in a consistent way 862with the rest of Acme. 863The middle button still executes commands, but in a style more suited 864to typescripts. Text selected with the middle button is treated as if 865it had been typed after the output point, much as a similar feature in 866</span><span style="font-size: 10pt"><tt>xterm</tt></span><span style="font-size: 10pt"> 867or 868</span><span style="font-size: 10pt"><tt>8½</tt></span><span style="font-size: 10pt">, 869and therefore causes it to be ‘executed’ by the application running in the window. 870Right button actions are reflected back to Acme but refer to the appropriate 871files because 872</span><span style="font-size: 10pt"><tt>win</tt></span><span style="font-size: 10pt"> 873places the name of the current directory in the tag of the window. 874If the shell is running, a simple shell function replacing the 875</span><span style="font-size: 10pt"><tt>cd</tt></span><span style="font-size: 10pt"> 876command can maintain the tag as the shell navigates the file system. 877This means, for example, that a right button click on a file mentioned in an 878</span><span style="font-size: 10pt"><tt>ls</tt></span><span style="font-size: 10pt"> 879listing opens the file within Acme. 880</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 881<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 882<span style="font-size: 10pt">Another Acme-specific program is a mail reader that begins by presenting, 883in a window, a listing of the messages in the user’s mailbox, one per line. 884Here the middle and right button actions are modified to refer to 885mail commands 886and messages, but the change feels natural. 887Clicking the right button on a line creates a new window and displays the 888message there, or, if it’s already displayed, moves the mouse to that window. 889The metaphor is that the mailbox is a directory whose constituent files are messages. 890The mail program also places some relevant commands in the tag lines of 891the windows; for example, executing the word 892</span><span style="font-size: 10pt"><tt>Reply</tt></span><span style="font-size: 10pt"> 893in a message’s tag creates a new window 894in which to compose a message to the sender of the original; 895</span><span style="font-size: 10pt"><tt>Post</tt></span><span style="font-size: 10pt"> 896then dispatches it. 897In such windows, the addressee is just a list of names 898on the first line of the body, which may be edited to add or change recipients. 899The program also monitors the mailbox, updating the ‘directory’ as new messages 900arrive. 901</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 902<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 903<span style="font-size: 10pt">The mail program is as simple as it sounds; all the work of interaction, 904editing, and management of the display is done by Acme. 905The only 906difficult sections of the 1200 907lines of code concern honoring the external protocols for managing 908the mailbox and connecting to 909</span><span style="font-size: 10pt"><tt>sendmail</tt></span><span style="font-size: 10pt">. 910</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 911<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 912<span style="font-size: 10pt">One of the things Acme does not provide directly is a facility like 913Sam’s command language to enable actions such as global substitution; 914within Acme, all editing is done manually. 915It is easy, though, to write external programs for such tasks. 916In this, Acme comes closer to the original intent of Oberon: 917a directory, 918</span><span style="font-size: 10pt"><tt>/acme/edit</tt></span><span style="font-size: 10pt">, 919contains a set of tools for repetitive editing and a template 920or ‘guide’ file that gives examples 921of its use. 922Acme’s editing guide, 923</span><span style="font-size: 10pt"><tt>/acme/edit/guide</tt></span><span style="font-size: 10pt">, 924looks like this: 925</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p> 926<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 927<span style="font-size: 9pt"><tt>e file | x ’/regexp/’ | c ’replacement’</tt></span></p> 928<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 929<span style="font-size: 9pt"><tt>e file:’0,$’ | x ’/.*word.*\n/’ | p -n</tt></span></p> 930<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 931<span style="font-size: 9pt"><tt>e file | pipe command args ...</tt></span></p> 932<p style="margin-top: 0; margin-bottom: 0.17in"></p> 933 934<p style="margin-top: 0; margin-bottom: 0.08in"></p> 935<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 936<span style="font-size: 10pt">The syntax is reminiscent of Sam’s command language, but here the individual 937one-letter commands are all stand-alone programs connected by pipes. 938Passed along the pipes are addresses, analogous to structural expressions 939in Sam terminology. 940The 941</span><span style="font-size: 10pt"><tt>e</tt></span><span style="font-size: 10pt"> 942command, unlike that of Sam, starts the process by generating the address 943(default dot, the highlighted selection) in the named files. 944The other commands are as in Sam: 945</span><span style="font-size: 10pt"><tt>p</tt></span><span style="font-size: 10pt"> 946prints the addressed text on standard output (the 947</span><span style="font-size: 10pt"><tt>-n</tt></span><span style="font-size: 10pt"> 948option is analogous to that of 949</span><span style="font-size: 10pt"><tt>grep</tt></span><span style="font-size: 10pt">, 950useful in combination with the right mouse button); 951</span><span style="font-size: 10pt"><tt>x</tt></span><span style="font-size: 10pt"> 952matches a regular expression to the addressed (incoming) text, 953subdividing the text; 954</span><span style="font-size: 10pt"><tt>c</tt></span><span style="font-size: 10pt"> 955replaces the text; and so on. Thus, global substitution throughout a file, 956which would be expressed in Sam as 957</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p> 958<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 959<span style="font-size: 9pt"><tt>0,$ x/regexp/ c/replacement/</tt></span></p> 960<p style="margin-top: 0; margin-bottom: 0.17in"></p> 961 962<p style="margin-top: 0; margin-bottom: 0.08in"></p> 963<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 964<span style="font-size: 10pt">in Acme’s editor becomes 965</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p> 966<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 967<span style="font-size: 9pt"><tt>e ’file:0,$’ | x ’/regexp/’ | c ’replacement’</tt></span></p> 968<p style="margin-top: 0; margin-bottom: 0.17in"></p> 969 970<p style="margin-top: 0; margin-bottom: 0.08in"></p> 971<p style="margin-top: 0; margin-bottom: 0.05in"></p> 972<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 973<span style="font-size: 10pt">To use the Acme editing commands, open 974</span><span style="font-size: 10pt"><tt>/acme/edit/guide</tt></span><span style="font-size: 10pt">, 975use the mouse and keyboard to edit one of the commands to the right form, 976and execute it with the middle button. 977Acme’s context rules find the appropriate binaries in 978</span><span style="font-size: 10pt"><tt>/acme/edit</tt></span><span style="font-size: 10pt"> 979rather than 980</span><span style="font-size: 10pt"><tt>/bin</tt></span><span style="font-size: 10pt">; 981the effect is to turn 982</span><span style="font-size: 10pt"><tt>/acme/edit</tt></span><span style="font-size: 10pt"> 983into a toolbox containing tools and instructions (the guide file) for their use. 984In fact, the source for these tools is also there, in the directory 985</span><span style="font-size: 10pt"><tt>/acme/edit/src</tt></span><span style="font-size: 10pt">. 986This setup allows some control of the file name space for binary programs; 987not only does it group related programs, it permits the use of common 988names for uncommon jobs. For example, the single-letter names would 989be unwise in a directory in everyone’s search path; here they are only 990visible when running editing commands. 991</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 992<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 993<span style="font-size: 10pt">In Oberon, 994such a collection would be called a 995</span><span style="font-size: 10pt"><i>tool</i></span><span style="font-size: 10pt"> 996and would consist 997of a set of entry points in a module and a menu-like piece of text containing 998representative commands that may be edited to suit and executed. 999There is, in fact, a tool called 1000</span><span style="font-size: 10pt"><tt>Edit</tt></span><span style="font-size: 10pt"> 1001in Oberon. 1002To provide related functionality, 1003Acme exploits the directory and file structure of the underlying 1004system, rather than the module structure of the language; 1005this fits well with Plan 9’s 1006file-oriented philosophy. 1007Such tools are central to the working of Oberon but they are 1008less used in Acme, at least so far. 1009The main reason is probably that Acme’s program interface permits 1010an external program to remain executing in the background, providing 1011its own commands as needed (for example, the 1012</span><span style="font-size: 10pt"><tt>Reply</tt></span><span style="font-size: 10pt"> 1013command in the mail program); Oberon uses tools to 1014implement such services because its must invoke 1015a fresh program for each command. 1016Also, 1017Acme’s better integration allows more 1018basic functions to be handled internally; the right mouse button 1019covers a lot of the basic utility of the editing tools in Oberon. 1020Nonetheless, as more applications are written for Acme, 1021many are sure to take this Oberon tool-like form. 1022</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p> 1023<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1024<span style="font-size: 10pt"><b>Comparison with other systems 1025</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1026<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1027<span style="font-size: 10pt">Acme’s immediate ancestor is Help [Pike92], an experimental system written 1028a few years ago as a first try at exploring some of Oberon’s ideas 1029in an existing operating system. 1030Besides much better engineering, Acme’s advances over Help 1031include the actions of the right button (Help had nothing comparable), 1032the ability to connect long-running programs to the user interface 1033(Help had no analog of the 1034</span><span style="font-size: 10pt"><tt>event</tt></span><span style="font-size: 10pt"> 1035file), 1036and the small but important change to split command output into 1037windows labeled with the directory in which the commands run. 1038</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1039<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1040<span style="font-size: 10pt">Most of Acme’s style, however, derives from the user interface and window 1041system of Oberon [Wirt89, Reis91]. 1042Oberon includes a programming language and operating system, 1043which Acme instead borrows from an existing system, Plan 9. 1044When I first saw Oberon, in 1988, I was struck by the 1045simplicity of its user interface, particularly its lack of menus 1046and its elegant use of multiple mouse buttons. 1047The system seemed restrictive, though—single process, 1048single language, no networking, event-driven programming—and 1049failed to follow through on some of its own ideas. 1050For example, the middle mouse button had to be pointed accurately and 1051the right button was essentially unused. 1052Acme does follow through: 1053to the basic idea planted by Oberon, it adds 1054the ability to run on different operating systems and hardware, 1055connection to existing applications including 1056interactive ones such as shells and debuggers, 1057support for multiple processes, 1058the right mouse button’s features, 1059the default actions and context-dependent properties 1060of execution and searching, 1061and a host of little touches such as moving the mouse cursor that make the system 1062more pleasant. 1063At the moment, though, Oberon does have one distinct advantage: it incorporates 1064graphical programs well into its model, an issue Acme has not yet faced. 1065</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1066<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1067<span style="font-size: 10pt">Acme shares with the Macintosh a desire to use the mouse well and it is 1068worth comparing the results. 1069The mouse on the Macintosh has a single button, so menus are essential 1070and the mouse must frequently move a long way 1071to reach the appropriate function. 1072An indication that this style has trouble is that applications provide 1073keyboard sequences to invoke menu selections and users often prefer them. 1074A deeper comparison is that the Macintosh uses pictures where Acme uses text. 1075In contrast to pictures, text can be edited quickly, created on demand, 1076and fine-tuned to the job at hand; consider adding an option to a command. 1077It is also self-referential; Acme doesn’t need menus because any text can be 1078in effect a menu item. 1079The result is that, although a Macintosh screen is certainly prettier and probably 1080more attractive, especially to beginners, an Acme screen is more dynamic 1081and expressive, at least for programmers and experienced users. 1082</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1083<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1084<span style="font-size: 10pt">For its role in the overall system, 1085Acme most resembles EMACS [Stal93]. 1086It is tricky to compare Acme to EMACS, though, because there are 1087many versions of EMACS and, since it is fully programmable, EMACS 1088can in principle do anything Acme does. 1089Also, Acme is much younger and therefore has not 1090had the time to acquire as many features. 1091The issue therefore is less what the systems can be programmed to do than 1092how they are used. 1093The EMACS versions that come closest to Acme’s style are those that 1094have been extended to provide a programming environment, usually 1095for a language such as LISP [Alle92, Lucid92]. 1096For richness of the existing interface, these EMACS versions are certainly superior to Acme. 1097On the other hand, Acme’s interface works equally well already for a variety 1098of languages; for example, one of its most enthusiastic users works almost 1099exclusively in Standard ML, a language nothing like C. 1100</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1101<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1102<span style="font-size: 10pt">Where Acme excels is in the smoothness of its interface. 1103Until recently, EMACS did not support the mouse especially well, 1104and even with the latest version providing features such as ‘extents’ 1105that can be programmed to behave much like Acme commands, 1106many users don’t bother to upgrade. 1107Moreover, in the versions that provide extents, 1108most EMACS packages don’t take advantage of them. 1109</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1110<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1111<span style="font-size: 10pt">The most important distinction is just that 1112EMACS is fundamentally keyboard-based, while 1113Acme is mouse-based. 1114</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1115<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1116<span style="font-size: 10pt">People who try Acme find it hard to go back to their previous environment. 1117Acme automates so much that to return to a traditional interface 1118is to draw attention to the extra work it requires. 1119</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p> 1120<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1121<span style="font-size: 10pt"><b>Concurrency in the implementation 1122</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1123<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1124<span style="font-size: 10pt">Acme is about 8,000 lines of code in Alef, a concurrent object-oriented language syntactically similar to C [Alef]. 1125Acme’s structure is a set of communicating 1126processes in a single address space. 1127One subset of the processes drives the display and user interface, 1128maintaining the windows; other processes forward mouse and keyboard 1129activity and implement the file server interface for external programs. 1130The language and design worked out well; 1131as explained elsewhere [Pike89, Gans93, Reppy93], 1132user interfaces built with concurrent systems 1133can avoid the clumsy 1134top-level event loop typical of traditional interactive systems. 1135</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1136<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1137<span style="font-size: 10pt">An example of the benefits of the multi-process style 1138is the management of the state of open 1139files held by clients of the file system interface. 1140The problem is that some I/O requests, 1141such as reading the 1142</span><span style="font-size: 10pt"><tt>event</tt></span><span style="font-size: 10pt"> 1143file, may block if no data is available, and the server must 1144maintain the state of (possibly many) requests until data appears. 1145For example, 1146in 1147</span><span style="font-size: 10pt"><tt>8½</tt></span><span style="font-size: 10pt">, 1148a single-process window system written in C, pending requests were queued in 1149a data structure associated with each window. 1150After activity in the window that might complete pending I/O, 1151the data structure was scanned for requests that could now finish. 1152This structure did not fit well with the rest of the program and, worse, 1153required meticulous effort 1154to guarantee correct behavior under all conditions 1155(consider raw mode, reads of partial lines, deleting a window, 1156multibyte characters, etc.). 1157</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1158<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1159<span style="font-size: 10pt">Acme instead creates a new dedicated process 1160for each I/O request. 1161This process coordinates with the rest of the system 1162using Alef’s synchronous communication; 1163its state implicitly encodes the state of 1164the I/O request and obviates the need for queuing. 1165The passage of the request through Acme proceeds as follows. 1166</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1167<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1168<span style="font-size: 10pt">Acme contains a file server process, F, that executes a 1169</span><span style="font-size: 10pt"><tt>read</tt></span><span style="font-size: 10pt"> 1170system call to receive a Plan 9 file protocol (9P) message from the client [AT&T92]. 1171The client blocks until Acme answers the request. 1172F communicates with an allocation process, M, 1173to acquire an object of type 1174</span><span style="font-size: 10pt"><tt>Xfid</tt></span><span style="font-size: 10pt"> 1175(‘executing fid’; fid is a 9P term) 1176to hold the request. 1177M sits in a loop (reproduced in Figure 2) waiting for either a request for 1178a new 1179</span><span style="font-size: 10pt"><tt>Xfid</tt></span><span style="font-size: 10pt"> 1180or notification that an existing one has finished its task. 1181When an 1182</span><span style="font-size: 10pt"><tt>Xfid</tt></span><span style="font-size: 10pt"> 1183is created, an associated process, X, 1184is also made. 1185M queues idle 1186</span><span style="font-size: 10pt"><tt>Xfids</tt></span><span style="font-size: 10pt">, 1187allocating new ones only when the list is empty. 1188Thus, there is always a pool of 1189</span><span style="font-size: 10pt"><tt>Xfids</tt></span><span style="font-size: 10pt">, 1190some executing, some idle. 1191</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1192<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1193<span style="font-size: 10pt">The 1194</span><span style="font-size: 10pt"><tt>Xfid</tt></span><span style="font-size: 10pt"> 1195object contains a channel, 1196</span><span style="font-size: 10pt"><tt>Xfid.c</tt></span><span style="font-size: 10pt">, 1197for communication with its process; 1198the unpacked message; and some associated functions, 1199mostly corresponding to 9P messages such as 1200</span><span style="font-size: 10pt"><tt>Xfid.write</tt></span><span style="font-size: 10pt"> 1201to handle a 9P write request. 1202</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1203<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1204<span style="font-size: 10pt">The file server process F parses the message to see its nature—open, 1205close, read, write, etc. Many messages, such as directory 1206lookups, can be handled immediately; these are responded to directly 1207and efficiently 1208by F without invoking the 1209</span><span style="font-size: 10pt"><tt>Xfid</tt></span><span style="font-size: 10pt">, 1210which is therefore maintained until the next message. 1211When a message, such as a write to the display, requires the attention 1212of the main display process and interlocked access to its data structures, 1213F enables X 1214by sending a function pointer on 1215</span><span style="font-size: 10pt"><tt>Xfid.c</tt></span><span style="font-size: 10pt">. 1216For example, if the message is a write, F executes 1217</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p> 1218<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1219<span style="font-size: 9pt"><tt>x->c <-= Xfid.write;</tt></span></p> 1220<p style="margin-top: 0; margin-bottom: 0.17in"></p> 1221 1222<p style="margin-top: 0; margin-bottom: 0.08in"></p> 1223<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1224<span style="font-size: 10pt">which sends 1225the address of 1226</span><span style="font-size: 10pt"><tt>Xfid.write</tt></span><span style="font-size: 10pt"> 1227on 1228</span><span style="font-size: 10pt"><tt>Xfid.c</tt></span><span style="font-size: 10pt">, 1229waking up X. 1230</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1231<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1232<span style="font-size: 10pt">The 1233</span><span style="font-size: 10pt"><tt>Xfid</tt></span><span style="font-size: 10pt"> 1234process, X, executes a simple loop: 1235</span></p><p style="margin-top: 0; margin-bottom: 0.08in"></p> 1236<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1237<span style="font-size: 9pt"><tt>void</tt></span></p> 1238<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1239<span style="font-size: 9pt"><tt>Xfid.ctl(Xfid *x)</tt></span></p> 1240<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1241<span style="font-size: 9pt"><tt>{</tt></span></p> 1242<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1243<span style="font-size: 9pt"><tt> for(;;){</tt></span></p> 1244<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1245<span style="font-size: 9pt"><tt> (*<-x->c)(x); /* receive and execute message */</tt></span></p> 1246<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1247<span style="font-size: 9pt"><tt> bflush(); /* synchronize bitmap display */</tt></span></p> 1248<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1249<span style="font-size: 9pt"><tt> cxfidfree <-= x; /* return to free list */</tt></span></p> 1250<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1251<span style="font-size: 9pt"><tt> }</tt></span></p> 1252<p style="line-height: 1.1em; margin-left: 1.28in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1253<span style="font-size: 9pt"><tt>}</tt></span></p> 1254<p style="margin-top: 0; margin-bottom: 0.17in"></p> 1255 1256<p style="margin-top: 0; margin-bottom: 0.08in"></p> 1257<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1258<span style="font-size: 10pt">Thus X 1259will wake up with the address of a function to call (here 1260</span><span style="font-size: 10pt"><tt>Xfid.write</tt></span><span style="font-size: 10pt">) 1261and execute it; once that completes, it returns itself to the pool of 1262free processes by sending its address back to the allocator. 1263</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1264<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1265<span style="font-size: 10pt">Although this sequence may seem complicated, it is just a few lines 1266of code and is in fact far simpler 1267than the management of the I/O queues in 1268</span><span style="font-size: 10pt"><tt>8½</tt></span><span style="font-size: 10pt">. 1269The hard work of synchronization is done by the Alef run time system. 1270Moreover, the code worked the first time, which cannot be said for the code in 1271</span><span style="font-size: 10pt"><tt>8½</tt></span><span style="font-size: 10pt">. 1272</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p> 1273<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1274<span style="font-size: 10pt"><b>Undo 1275</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1276<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1277<span style="font-size: 10pt">Acme provides a general undo facility like that of Sam, permitting 1278textual changes to be unwound arbitrarily. 1279The implementation is superior to Sam’s, though, 1280with much higher performance and the ability to ‘redo’ changes. 1281</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1282<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1283<span style="font-size: 10pt">Sam uses 1284a multi-pass algorithm that builds 1285a transcript of changes to be made simultaneously 1286and then executes them atomically. 1287This was thought necessary because the elements of a repetitive 1288command such as a global substitution should all be applied to the same 1289initial file and implemented simultaneously; forming the complete 1290transcript before executing any of the changes avoids the 1291cumbersome management of addresses in a changing file. 1292Acme, however, doesn’t have this problem; global substitution 1293is controlled externally and may be made incrementally by exploiting 1294an observation: if the changes are sorted in address order and 1295executed in reverse, changes will not invalidate the addresses of 1296pending changes. 1297</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1298<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1299<span style="font-size: 10pt">Acme therefore avoids the initial transcript. Instead, changes are applied 1300directly to the file, with an undo transcript recorded in a separate list. 1301For example, when text is added to a window, it is added directly and a record 1302of what to delete to restore the state is appended to the undo list. 1303Each undo action and the file are marked with a sequence number; 1304actions with the same sequence number are considered a unit 1305to be undone together. 1306The invariant state of the structure 1307is that the last action in the undo list applies to the current state of the file, 1308even if that action is one of a related set from, for example, a global substitute. 1309(In Sam, a related set of actions needed to be undone simultaneously.) 1310To undo an action, pop the last item on the undo list, apply it to the file, 1311revert it, and append it to a second, redo list. 1312To redo an action, do the identical operation with the lists interchanged. 1313The expensive operations occur 1314only when actually undoing; in normal editing the overhead is minor. 1315For example, Acme reads files about seven times faster than Sam, partly 1316because of this improvement and partly because of a cleaner implementation. 1317</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1318<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1319<span style="font-size: 10pt">Acme uses a temporary file to hold the text, keeping in memory only the 1320visible portion, and therefore can edit large files comfortably 1321even on small-memory machines such as laptops. 1322</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p> 1323<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1324<span style="font-size: 10pt"><b>Future 1325</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1326<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1327<span style="font-size: 10pt">Acme is still under development. 1328Some things are simply missing. 1329For example, Acme should support non-textual graphics, but this is being 1330deferred until it can be done using a new graphics model being developed 1331for Plan 9. Also, it is undecided how Acme’s style of interaction should best be 1332extended to graphical applications. 1333On a smaller scale, although the system feels smooth and comfortable, 1334work continues to tune the heuristics and 1335try new ideas for the user interface. 1336</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1337<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1338<span style="font-size: 10pt">There need to be more programs that use Acme. Browsers for 1339Usenet and AP News articles, the Oxford English Dictionary, and other 1340such text sources exist, but more imaginative applications will 1341be necessary to prove that Acme’s approach is viable. 1342One that has recently been started is an interface to the debugger Acid [Wint94], 1343although it is still 1344unclear what form it will ultimately take. 1345</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1346<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1347<span style="font-size: 10pt">Acme shows that it is possible to make a user interface a stand-alone component 1348of an interactive environment. By absorbing more of the interactive 1349functionality than a simple window system, Acme off-loads much of the 1350computation from its applications, which helps keep them small and 1351consistent in their interface. Acme can afford to dedicate 1352considerable effort to making that interface as good as possible; the result 1353will benefit the entire system. 1354</span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1355<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1356<span style="font-size: 10pt">Acme is complete and useful enough to attract users. 1357Its comfortable user interface, 1358the ease with which it handles multiple tasks and 1359programs in multiple directories, 1360and its high level of integration 1361make it addictive. 1362Perhaps most telling, 1363Acme shows that typescripts may not be the most 1364productive interface to a time-sharing system. 1365</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p> 1366<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1367<span style="font-size: 10pt"><b>Acknowledgements 1368</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1369<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.35in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1370<span style="font-size: 10pt">Howard Trickey, Acme’s first user, suffered buggy versions gracefully and made 1371many helpful suggestions. Chris Fraser provided the necessary insight for the Acme editing 1372commands. 1373</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p> 1374<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1375<span style="font-size: 10pt"><b>References 1376</b></span></p><p style="margin-top: 0; margin-bottom: 0.05in"></p> 1377<p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1378<span style="font-size: 10pt">[Alef] P. Winterbottom, 1379‘‘Alef Language Reference Manual’’, 1380</span><span style="font-size: 10pt"><i>Plan 9 Programmer’s Manual, 1381</i></span><span style="font-size: 10pt">AT&T Bell Laboratories, 1382Murray Hill, NJ, 13831992; 1384revised in this volume. 1385</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1386<span style="font-size: 10pt">[Alle92] 1387</span><span style="font-size: 10pt"><i>Allegro Common Lisp user Guide, Vol 2, 1388</i></span><span style="font-size: 10pt">Chapter 14, "The Emacs-Lisp Interface". 1389March 1992. 1390</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1391<span style="font-size: 10pt">[AT&T92] Plan 9 Programmer’s manual, Murray Hill, New Jersey, 1992. 1392</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1393<span style="font-size: 10pt">[Far89] Far too many people, XTERM(1), Massachusetts Institute of Technology, 1989. 1394</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1395<span style="font-size: 10pt">[Gans93] Emden R. Gansner and John H. Reppy, ‘‘A Multi-threaded Higher-order User Interface Toolkit’’, in 1396</span><span style="font-size: 10pt"><i>Software Trends, Volume 1, 1397User Interface Software, 1398</i></span><span style="font-size: 10pt">Bass and Dewan (Eds.), 1399John Wiley & Sons 1993, 1400pp. 61-80. 1401</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1402<span style="font-size: 10pt">[Lucid92] Richard Stallman and Lucid, Inc., 1403</span><span style="font-size: 10pt"><i>Lucid GNU EMACS Manual, 1404</i></span><span style="font-size: 10pt">March 1992. 1405</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1406<span style="font-size: 10pt">[Pike87] Rob Pike, ‘‘The Text Editor </span><span style="font-size: 10pt"><tt>sam</tt></span><span style="font-size: 10pt">’’, Softw. - Pract. and Exp., Nov 1987, Vol 17 #11, pp. 813-845; reprinted in this volume. 1407</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1408<span style="font-size: 10pt">[Pike88] Rob Pike, ‘‘Window Systems Should Be Transparent’’, Comp. Sys., Summer 1988, Vol 1 #3, pp. 279-296. 1409</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1410<span style="font-size: 10pt">[Pike89] Rob Pike, ‘‘A Concurrent Window System’’, Comp. Sys., Spring 1989, Vol 2 #2, pp. 133-153. 1411</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1412<span style="font-size: 10pt">[PPTTW93] Rob Pike, Dave Presotto, Ken Thompson, Howard Trickey, and Phil Winterbottom, ‘‘The Use of Name Spaces in Plan 9’’, 1413Op. Sys. Rev., Vol. 27, No. 2, April 1993, pp. 72-76, 1414reprinted in this volume. 1415</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1416<span style="font-size: 10pt">[Pike91] Rob Pike, ‘‘8½, the Plan 9 Window System’’, USENIX Summer Conf. Proc., Nashville, June, 1991, pp. 257-265, 1417reprinted in this volume. 1418</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1419<span style="font-size: 10pt">[Pike92] Rob Pike, ‘‘A Minimalist Global User Interface’’, Graphics Interface ’92 Proc., Vancouver, 1992, pp. 282-293. An earlier version appeared under the same title in USENIX Summer Conf. Proc., Nashville, June, 1991, pp. 267-279. 1420</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1421<span style="font-size: 10pt">[Pike93] Rob Pike and Ken Thompson, ‘‘Hello World or Καλημέρα κόσμε or 1422</span><span style="font-size: 10pt">こんにちは 世界</span><span style="font-size: 10pt">’’, USENIX Winter Conf. Proc., San Diego, 1993, pp. 43-50, 1423reprinted in this volume. 1424</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1425<span style="font-size: 10pt">[Pres93] Dave Presotto and Phil Winterbottom, ‘‘The Organization of Networks in Plan 9’’, Proc. Usenix Winter 1993, pp. 271-287, San Diego, CA, 1426reprinted in this volume. 1427</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1428<span style="font-size: 10pt">[Reis91] Martin Reiser, </span><span style="font-size: 10pt"><i>The Oberon System,</i></span><span style="font-size: 10pt"> Addison Wesley, New York, 1991. 1429</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1430<span style="font-size: 10pt">[Reppy93] John H. Reppy, 1431‘‘CML: A higher-order concurrent language’’, Proc. SIGPLAN’91 Conf. on Programming, Lang. Design and Impl., June, 1991, pp. 293-305. 1432</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1433<span style="font-size: 10pt">[Sche86] Robert W. Scheifler and Jim Gettys, 1434‘‘The X Window System’’, 1435ACM Trans. on Graph., Vol 5 #2, pp. 79-109. 1436</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1437<span style="font-size: 10pt">[Stal93] Richard Stallman, 1438</span><span style="font-size: 10pt"><i>Gnu Emacs Manual, 9th edition, Emacs version 19.19, 1439</i></span><span style="font-size: 10pt">MIT. 1440</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1441<span style="font-size: 10pt">[Swei86] Daniel Sweinhart, Polle Zellweger, Richard Beach, and Robert Hagmann, 1442‘‘A Structural View of the Cedar Programming Environment’’, 1443ACM Trans. Prog. Lang. and Sys., Vol. 8, No. 4, pp. 419-490, Oct. 1986. 1444</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1445<span style="font-size: 10pt">[Wint94], Philip Winterbottom, ‘‘Acid: A Debugger based on a Language’’, USENIX Winter Conf. Proc., San Francisco, CA, 1993, 1446reprinted in this volume. 1447</span></p><p style="line-height: 1.2em; margin-left: 1.00in; text-indent: 0.00in; margin-right: 1.00in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1448<span style="font-size: 10pt">[Wirt89] N. Wirth and J. Gutknecht, ‘‘The Oberon System’’, Softw. - Prac. and Exp., Sep 1989, Vol 19 #9, pp 857-894. 1449</span></p><p style="margin-top: 0; margin-bottom: 0.50in"></p> 1450<p style="margin-top: 0; margin-bottom: 0.17in"></p> 1451<p style="line-height: 1.2em; margin-left: 1.50in; text-indent: 0.35in; margin-right: 1.50in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1452<span style="font-size: 10pt"></span><span style="font-size: 10pt"><b>Notes</b></span><span style="font-size: 10pt"> 1453</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p> 1454<p style="margin-top: 0; margin-bottom: 0.17in"></p> 1455 1456<p style="line-height: 1.2em; margin-left: 1.50in; text-indent: 0.00in; margin-right: 1.50in; margin-top: 0; margin-bottom: 0; text-align: justify;"> 1457<span style="font-size: 10pt">Originally appeared in 1458</span><span style="font-size: 10pt"><i>Proc. of the Winter 1994 USENIX Conf., 1459</i></span><span style="font-size: 10pt">pp. 223-234, 1460San Francisco, CA 1461</span></p><p style="margin-top: 0; margin-bottom: 0.17in"></p> 1462<p style="margin-top: 0; margin-bottom: 0.17in"></p> 1463 1464</body> 1465</html> 1466 1467
