-
Notifications
You must be signed in to change notification settings - Fork 2
/
macro-0.html
402 lines (261 loc) · 10.6 KB
/
macro-0.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
<title>macro-0</title>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<meta content="37.444542, -122.161050" name="ICBM" />
<link media="all" href="/stylesheets/nu.css" type ="text/css" rel="stylesheet" />
</head>
<body>
<div id="container">
<div id="header">
<div style="float:left; margin-right:10px">
<img src="/files/recycle-s.png" height="50" alt="recycling symbol" />
</div>
<div style="float:left">
<h1><a href="/">Programming Nu</a></h1>
<h3><a href="https://github.com/programming-nu">github.com/programming-nu</a></h3>
</div>
</div>
<div id="content">
<div class="atomentry">
<div class="content" style="margin-bottom:10px">
<h1>macro-0</h1>
<blockquote>
<p>Note: <strong>macro-0</strong> is the new name for the original Nu macro operator. The new <a href="/operators#macros"><strong>macro</strong></a> operator requires an argument list declaration and therefore is not backward-compatible with the original macro operator. <strong>macro-0</strong> is still available in Nu, so if you do not want to rewrite your old macros using the new macro format, you can just rename your existing <strong>macro</strong> calls to <strong>macro-0</strong> and everything should still work as before.</p>
</blockquote>
<p><strong>macro-0</strong> creates a named macro in the current evaluation
context. It expects two arguments: the macro name, followed by
the body of the macro. Inside the macro, its arguments may be accessed by referring to the <strong>margs</strong> special variable.</p>
<p>When a block is created with the <strong>macro-0</strong> operator, no context is kept. Instead, when the macro is evaluated, all block evaluation takes place in the caller's context.
To access the macro's arguments, a special symbol <strong>margs</strong> is pushed into that context (and if there's an existing value, that's saved until the macro finishes).
The <strong>margs</strong> symbol is just the list of unevaluated arguments to the macro; the macro itself determines when and how they are evaluated. Next, any names in the block that begin with a double underscore are replaced with generated symbols, and then the block is evaluated. Here's a simple example:</p>
<pre>
(macro-0 factorial
(set __x (eval (car margs)))
(if (== __x 0)
(then 1)
(else (* (factorial (- __x 1)) __x))))
</pre>
<p>In practice, you'd never compute factorials like this, but it illustrates an important problem that can occur with macros. Since macros are evaluated in the caller's context, each recursive evaluation of <strong>factorial</strong> potentially sets our
double-underscored <strong>x</strong> to a new value.
That would be bad, so each time we evaluate this macro in Nu, the double-underscored <strong>x</strong> is replaced with a new automatically-generated name that is guaranteed to be unique.</p>
</div>
<div class="extended">
</div>
</div> <!-- atomentry -->
</div> <!-- content -->
<div id="sidebar">
<div class="sidebar-node">
<h2><a href="/about">About Nu</a></h2>
</div>
<div class="sidebar-node">
<h2><a href="http://groups.google.com/group/programming-nu/topics">Google Group:<br/>Programming Nu</a></h2>
</div>
<div class="sidebar-node">
<h2><a href="/downloads">Download Nu</a></h2>
</div>
<div class="sidebar-node">
<h2>Git Repositories</h2>
<ul>
<li><a href="https://github.com/programming-nu/nu">nu</a></li>
<li><a href="https://github.com/programming-nu/programming-nu">programming-nu</a></li>
</ul>
</div>
<div class="sidebar-node">
<h2><a href="/documentation">Documentation</a></h2>
<ul>
<li><a href="/installing">Installing Nu</a></li>
<li><a href="/usage">Using Nu</a></li>
<li><a href="/embedding">Embedding Nu</a></li>
<li><a href="/reference">Nu Reference</a></li>
<li><a href="/syntax">- Syntax</a></li>
<li><a href="/operators">- Operators</a></li>
<li><a href="/types">- Types</a></li>
<li><a href="/doc/index.html">- Class Reference</a></li>
<li><a href="/help">Getting and Providing Help</a></li>
<li><a href="/debugging">Debugging Nu Programs</a></li>
<li><a href="/textmate">A Bundle for TextMate Users</a></li>
</ul>
</div>
<div class="sidebar-node">
<h2><a href="/examples">Examples</a></h2>
<ul>
<li><a href="/randomapp">RandomApp</a></li>
<li><a href="/randomappwithnibfile">RandomAppWithNibFile</a></li>
<li><a href="/currencyconverter">Currency Converter</a></li>
<li><a href="/nurocks">NuRocks</a></li>
<li><a href="/console">Console</a></li>
<li><a href="/growler">Growler</a></li>
<li><a href="/benwanu">Benwanu</a></li>
<li><a href="/screensaver">Screen Saver</a></li>
<li><a href="/maildemo">MailDemo</a></li>
<li><a href="/nuanywhere">NuAnywhere</a></li>
</ul>
</div>
<div class="sidebar-node">
<h2><a href="/tools">Tools</a></h2>
<ul>
<li><a href="/nuke">nuke, a make utility</a></li>
<li><a href="/nubile">nubile, a code formatter</a></li>
<li><a href="/nutest">nutest, a testing tool</a></li>
<li><a href="/nudoc">nudoc, a documentation generator</a></li>
<li><a href="/nutemplate">nutemplate, a templating tool</a></li>
<li><a href="/nubake">nubake, a code generation tool</a></li>
</ul>
</div>
<div class="sidebar-node">
<h2><a href="/">Archives</a></h2>
<ul>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">July 2019</li>
<li>
<a href="/posts/2019/07/25/programming-nu-on-github">
Programming Nu on GitHub</a>
</li>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">April 2013</li>
<li>
<a href="/posts/2013/04/14/Nu-2.1.0">
Nu-2.1.0</a>
</li>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">September 2011</li>
<li>
<a href="/posts/2011/09/02/Nu-2.0.1">
Nu-2.0.1</a>
</li>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">August 2011</li>
<li>
<a href="/posts/2011/08/25/Nu-2.0.0">
Nu-2.0.0</a>
</li>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">December 2009</li>
<li>
<a href="/posts/2009/12/09/stability">
Nu Seems Stable (by Jason Grossman)</a>
</li>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">November 2009</li>
<li>
<a href="/posts/2009/11/22/vi">
vi tips for Nu</a>
</li>
<li>
<a href="/posts/2009/11/17/Nu-0.4.0">
Nu-0.4.0</a>
</li>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">January 2009</li>
<li>
<a href="/posts/2009/01/02/macros">
Macros</a>
</li>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">December 2008</li>
<li>
<a href="/posts/2008/12/03/Nu-0.3.3">
Nu-0.3.3</a>
</li>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">June 2008</li>
<li>
<a href="/posts/2008/06/08/Nu-0.3.2">
Nu-0.3.2</a>
</li>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">May 2008</li>
<li>
<a href="/posts/2008/05/23/cocoa-programming-with-nu">
Cocoa Programming with Nu</a>
</li>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">March 2008</li>
<li>
<a href="/posts/2008/03/24/Nu-0.3.1">
Nu-0.3.1</a>
</li>
<li>
<a href="/posts/2008/03/21/announcing-nu">
Announcing Nu: The Video</a>
</li>
<li>
<a href="/posts/2008/03/18/nu-on-github">
Nu on github</a>
</li>
<li>
<a href="/posts/2008/03/14/new-platforms">
Linux and the iPhone</a>
</li>
<li>
<a href="/posts/2008/03/12/new-license">
Apache License, v. 2.0</a>
</li>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">February 2008</li>
<li>
<a href="/posts/2008/02/13/Nu-0.3.0">
Nu-0.3.0</a>
</li>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">December 2007</li>
<li>
<a href="/posts/2007/12/12/nupagepacker">
NuPagePacker</a>
</li>
<li>
<a href="/posts/2007/12/12/Nu-0.2.4">
Nu-0.2.4</a>
</li>
<li>
<a href="/posts/2007/12/07/Nu-0.2.3">
Nu-0.2.3</a>
</li>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">November 2007</li>
<li>
<a href="/posts/2007/11/26/Nu-0.2.2">
Nu-0.2.2</a>
</li>
<li>
<a href="/posts/2007/11/25/a-delicious-nu-screencast">
A Delicious Nu Screencast</a>
</li>
<li>
<a href="/posts/2007/11/12/Nu-0.2.1">
Nu-0.2.1</a>
</li>
<li style="font-weight:bold; font-size:smaller; background:#eee; line-height:100%">October 2007</li>
<li>
<a href="/posts/2007/10/17/new-literal-forms-in-nu">
New Literal Forms in Nu</a>
</li>
<li>
<a href="/posts/2007/10/17/escape-sequences-in-nu-strings">
Escape Sequences in Nu Strings</a>
</li>
<li>
<a href="/posts/2007/10/17/closures-in-nu">
Closures in Nu</a>
</li>
<li>
<a href="/posts/2007/10/17/Nu-0.2.0">
Nu-0.2.0</a>
</li>
<li>
<a href="/posts/2007/10/11/screen-savers-and-plugins">
Screen Savers and Plugins</a>
</li>
<li>
<a href="/posts/2007/10/10/markdown-in-nu">
Markdown in Nu</a>
</li>
<li>
<a href="/posts/2007/10/05/functional-nu">
Functional Aspects of Nu</a>
</li>
<li>
<a href="/posts/2007/10/04/randomapp-with-nibfile">
New Example: Nib Files</a>
</li>
<li>
<a href="/posts/2007/10/01/welcome">
Welcome</a>
</li>
</ul>
</div>
<div class="sidebar-node">
<h2><a href="/legal">Legal Details</a></h2>
</div>
</div> <!-- sidebar -->
</div><!-- container -->
</body>
</html>