mlton-doc 20100608-5 / usr / share / doc / mlton / guide / SMLNJDeviations

This file is indexed.

/usr/share/doc/mlton/guide/SMLNJDeviations is in mlton-doc 20100608-5.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below. 

  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
403
404
405
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta name="robots" content="index,nofollow">



<title>SMLNJDeviations - MLton Standard ML Compiler (SML Compiler)</title>
<link rel="stylesheet" type="text/css" charset="iso-8859-1" media="all" href="common.css">
<link rel="stylesheet" type="text/css" charset="iso-8859-1" media="screen" href="screen.css">
<link rel="stylesheet" type="text/css" charset="iso-8859-1" media="print" href="print.css">


<link rel="Start" href="Home">


</head>

<body lang="en" dir="ltr">

<script src="http://www.google-analytics.com/urchin.js" type="text/javascript">
</script>
<script type="text/javascript">
_uacct = "UA-833377-1";
urchinTracker();
</script>
<table bgcolor = lightblue cellspacing = 0 style = "border: 0px;" width = 100%>
  <tr>
    <td style = "
		border: 0px;
		color: darkblue; 
		font-size: 150%;
		text-align: left;">
      <a class = mltona href="Home">MLton MLTONWIKIVERSION</a>
    <td style = "
		border: 0px;
		font-size: 150%;
		text-align: center;
		width: 50%;">
      SMLNJDeviations
    <td style = "
		border: 0px;
		text-align: right;">
      <table cellspacing = 0 style = "border: 0px">
        <tr style = "vertical-align: middle;">
      </table>
  <tr style = "background-color: white;">
    <td colspan = 3
	style = "
		border: 0px;
		font-size:70%;
		text-align: right;">
      <a href = "Home">Home</a>
      &nbsp;<a href = "TitleIndex">Index</a>
      &nbsp;
</table>
<div id="content" lang="en" dir="ltr">
Here are some deviations of <a href="SMLNJ">SML/NJ</a> from  <a href="DefinitionOfStandardML">The Definition of Standard ML</a>.  Some of these are documented in the  <a class="external" href="http://www.smlnj.org/doc/Conversion/index.html"><img src="moin-www.png" alt="[WWW]" height="11" width="11">SML '97 Conversion Guide</a>. Since MLton does not deviate from the Definition, you should look here if you are having trouble porting a program from MLton to SML/NJ or vice versa.  If you discover other deviations of SML/NJ that aren't listed here, please send mail to  <a class="external" href="mailto:MLton@mlton.org"><img src="moin-email.png" alt="[MAILTO]" height="10" width="14">MLton@mlton.org</a>. 
    <ul>

    <li>
<p>
 SML/NJ allows spaces in long identifiers, as in <tt>S&nbsp;.&nbsp;x</tt>.  Section 2.5 of the Definition implies that <tt>S&nbsp;.&nbsp;x</tt> should be treated as three separate lexical items. 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ allows <tt>op</tt> to appear in <tt>val</tt> specifications: 
<pre class=code>
<B><FONT COLOR="#0000FF">signature</FONT></B> FOO = <B><FONT COLOR="#0000FF">sig</FONT></B>
   <B><FONT COLOR="#A020F0">val</FONT></B> <B><FONT COLOR="#A020F0">op</FONT></B> + : int * int -&gt; int
<B><FONT COLOR="#0000FF">end</FONT></B>
</PRE>
 The grammar on page 14 of the Definition does not allow it. Recent versions of SML/NJ do give a warning. 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ rejects 
<pre class=code>
(<B><FONT COLOR="#A020F0">op</FONT></B> *)
</PRE>
 as an unmatched close comment. 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ allows <tt>=</tt> to be rebound by the declaration: 
<pre class=code>
<B><FONT COLOR="#A020F0">val</FONT></B> <B><FONT COLOR="#A020F0">op</FONT></B> = = <B><FONT COLOR="#5F9EA0">13</FONT></B>
</PRE>
 This is explicitly forbidden on page 5 of the Definition. Recent versions of SML/NJ do give a warning. 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ allows rebinding <tt>true</tt>, <tt>false</tt>, <tt>nil</tt>, <tt>::</tt>, and <tt>ref</tt> by the declarations: 
<pre class=code>
<B><FONT COLOR="#A020F0">fun</FONT></B> true () = ()
<B><FONT COLOR="#A020F0">fun</FONT></B> false () = ()
<B><FONT COLOR="#A020F0">fun</FONT></B> nil () = ()
<B><FONT COLOR="#A020F0">fun</FONT></B> <B><FONT COLOR="#A020F0">op</FONT></B> :: () = ()
<B><FONT COLOR="#A020F0">fun</FONT></B> ref () = ()
</PRE>
 This is explicitly forbidden on page 9 of the Definition. 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ extends the syntax of the language to allow vector expressions and patterns like the following: 
<pre class=code>
<B><FONT COLOR="#A020F0">val</FONT></B> v = #[<B><FONT COLOR="#5F9EA0">1</FONT></B>,<B><FONT COLOR="#5F9EA0">2</FONT></B>,<B><FONT COLOR="#5F9EA0">3</FONT></B>]
<B><FONT COLOR="#A020F0">val</FONT></B> #[x,y,z] = v
</PRE>
 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ extends the syntax of the language to allow <em>or patterns</em> like the following: 
<pre class=code>
<B><FONT COLOR="#A020F0">datatype</FONT></B><B><FONT COLOR="#228B22"> foo </FONT></B>=<B><FONT COLOR="#228B22"> <FONT COLOR="#B8860B">Foo</FONT> <B><FONT COLOR="#A020F0">of</FONT></B> int </FONT></B>|<B><FONT COLOR="#228B22"> <FONT COLOR="#B8860B">Bar</FONT> <B><FONT COLOR="#A020F0">of</FONT></B> int
</FONT></B><B><FONT COLOR="#A020F0">val</FONT></B> (Foo x | Bar x) = Foo <B><FONT COLOR="#5F9EA0">13</FONT></B>
</PRE>
 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ allows higher-order functors, that is, functors can be components of structures and can be passed as functor arguments and returned as functor results.  As a consequence, SML/NJ allows abbreviated functor definitions, as in the following: 
<pre class=code>
<B><FONT COLOR="#0000FF">signature</FONT></B> S =
  <B><FONT COLOR="#0000FF">sig</FONT></B>
    <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t
    </FONT></B><B><FONT COLOR="#A020F0">val</FONT></B> x: t
  <B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">functor</FONT></B> F (<B><FONT COLOR="#0000FF">structure</FONT></B> A: S): S = 
  <B><FONT COLOR="#0000FF">struct</FONT></B>
    <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> A.t * A.t
    </FONT></B><B><FONT COLOR="#A020F0">val</FONT></B> x = (A.x, A.x)
  <B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">functor</FONT></B> G = F
</PRE>
  
</p>
</li>
    <li class="gap">
<p>
 SML/NJ extends the syntax of the language to allow functor and signature definitions to occur within the scope of <tt>local</tt> and <tt>structure</tt> declarations. 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ allows duplicate type specifications in signatures when the duplicates are introduced by <tt>include</tt>, as in the following: 
<pre class=code>
<B><FONT COLOR="#0000FF">signature</FONT></B> SIG1 =
   <B><FONT COLOR="#0000FF">sig</FONT></B>
      <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t
      </FONT></B><B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> u
   </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">signature</FONT></B> SIG2 =
   <B><FONT COLOR="#0000FF">sig</FONT></B>
      <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t
      </FONT></B><B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> v
   </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">signature</FONT></B> SIG =
   <B><FONT COLOR="#0000FF">sig</FONT></B>
      <B><FONT COLOR="#0000FF">include</FONT></B> SIG1
      <B><FONT COLOR="#0000FF">include</FONT></B> SIG2
   <B><FONT COLOR="#0000FF">end</FONT></B>
</PRE>
 This is disallowed by rule 77 of the Definition. 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ allows sharing constraints between type abbreviations in signatures, as in the following: 
<pre class=code>
<B><FONT COLOR="#0000FF">signature</FONT></B> SIG =
   <B><FONT COLOR="#0000FF">sig</FONT></B>
      <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> int * int
      </FONT></B><B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> u </FONT></B>=<B><FONT COLOR="#228B22"> int * int
      </FONT></B><B><FONT COLOR="#0000FF">sharing</FONT></B> <B><FONT COLOR="#0000FF">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> u
   </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B>
</PRE>
 These are disallowed by rule 78 of the Definition.  Recent versions of SML/NJ correctly disallow sharing constraints between type abbreviations in signatures. 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ disallows multiple <tt>where&nbsp;type</tt> specifications of the same type name, as in the following 
<pre class=code>
<B><FONT COLOR="#0000FF">signature</FONT></B> S =
  <B><FONT COLOR="#0000FF">sig</FONT></B>
     <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t
     </FONT></B><B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> u </FONT></B>=<B><FONT COLOR="#228B22"> t
  </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B>
  <B><FONT COLOR="#0000FF">where</FONT></B> <B><FONT COLOR="#0000FF">type</FONT></B><B><FONT COLOR="#228B22"> u </FONT></B>=<B><FONT COLOR="#228B22"> int
</FONT></B></PRE>
 This is allowed by rule 84 of the Definition. 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ allows <tt>and</tt> in <tt>sharing</tt> specs in signatures, as in 
<pre class=code>
<B><FONT COLOR="#A020F0">signature</FONT></B> S =
   <B><FONT COLOR="#A020F0">sig</FONT></B>
      <B><FONT COLOR="#A020F0">type</FONT></B> t
      <B><FONT COLOR="#A020F0">type</FONT></B> u
      <B><FONT COLOR="#A020F0">type</FONT></B> v
      <B><FONT COLOR="#A020F0">sharing</FONT></B> <B><FONT COLOR="#A020F0">type</FONT></B> t = u
      <B><FONT COLOR="#A020F0">and</FONT></B> <B><FONT COLOR="#A020F0">type</FONT></B> u = v
   <B><FONT COLOR="#A020F0">end</FONT></B>
</PRE>
 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ does not expand the <tt>withtype</tt> derived form as described by the Definition.  According to page 55 of the Definition, the type bindings of a <tt>withtype</tt> declaration are substituted simultaneously in the connected datatype.  Consider the following program. 
<pre class=code>
<B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> u </FONT></B>=<B><FONT COLOR="#228B22"> real </FONT></B>;
<B><FONT COLOR="#A020F0">datatype</FONT></B><B><FONT COLOR="#228B22"> a </FONT></B>=<B><FONT COLOR="#228B22">
    <FONT COLOR="#B8860B">A</FONT> <B><FONT COLOR="#A020F0">of</FONT></B> t
  </FONT></B>|<B><FONT COLOR="#228B22"> <FONT COLOR="#B8860B">B</FONT> <B><FONT COLOR="#A020F0">of</FONT></B> u
</FONT></B><B><FONT COLOR="#A020F0">withtype</FONT></B><B><FONT COLOR="#228B22"> u </FONT></B>=<B><FONT COLOR="#228B22"> int
</FONT></B><B><FONT COLOR="#A020F0">and</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> u
</FONT></B></PRE>
 According to the Definition, it should be expanded to the following. 
<pre class=code>
<B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> u </FONT></B>=<B><FONT COLOR="#228B22"> real </FONT></B>;
<B><FONT COLOR="#A020F0">datatype</FONT></B><B><FONT COLOR="#228B22"> a </FONT></B>=<B><FONT COLOR="#228B22">
    <FONT COLOR="#B8860B">A</FONT> <B><FONT COLOR="#A020F0">of</FONT></B> u
  </FONT></B>|<B><FONT COLOR="#228B22"> <FONT COLOR="#B8860B">B</FONT> <B><FONT COLOR="#A020F0">of</FONT></B> int </FONT></B>;
<B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> u </FONT></B>=<B><FONT COLOR="#228B22"> int
</FONT></B><B><FONT COLOR="#A020F0">and</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> u 
</FONT></B></PRE>
 However, SML/NJ expands <tt>withtype</tt> bindings sequentially, meaning that earlier bindings are expanded within later ones. Hence,  the above program is expanded to the following. 
<pre class=code>
<B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> u </FONT></B>=<B><FONT COLOR="#228B22"> real </FONT></B>;
<B><FONT COLOR="#A020F0">datatype</FONT></B><B><FONT COLOR="#228B22"> a </FONT></B>=<B><FONT COLOR="#228B22">
    <FONT COLOR="#B8860B">A</FONT> <B><FONT COLOR="#A020F0">of</FONT></B> int
  </FONT></B>|<B><FONT COLOR="#228B22"> <FONT COLOR="#B8860B">B</FONT> <B><FONT COLOR="#A020F0">of</FONT></B> int </FONT></B>;
<B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> u </FONT></B>=<B><FONT COLOR="#228B22"> int
</FONT></B><B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> int
</FONT></B></PRE>
 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ allows <tt>withtype</tt> specifications in signatures. 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ allows a <tt>where</tt> structure specification that is similar to a <tt>where&nbsp;type</tt> specification.  For example: 
<pre class=code>
<B><FONT COLOR="#0000FF">structure</FONT></B> S = <B><FONT COLOR="#0000FF">struct</FONT></B> <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> int </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">signature</FONT></B> SIG =
  <B><FONT COLOR="#0000FF">sig</FONT></B>
     <B><FONT COLOR="#0000FF">structure</FONT></B> T : <B><FONT COLOR="#0000FF">sig</FONT></B> <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B>
  <B><FONT COLOR="#0000FF">end</FONT></B> <B><FONT COLOR="#0000FF">where</FONT></B> T = S
</PRE>
 This is equivalent to: 
<pre class=code>
<B><FONT COLOR="#0000FF">structure</FONT></B> S = <B><FONT COLOR="#0000FF">struct</FONT></B> <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> int </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">signature</FONT></B> SIG =
  <B><FONT COLOR="#0000FF">sig</FONT></B>
     <B><FONT COLOR="#0000FF">structure</FONT></B> T : <B><FONT COLOR="#0000FF">sig</FONT></B> <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B>
  <B><FONT COLOR="#0000FF">end</FONT></B> <B><FONT COLOR="#0000FF">where</FONT></B> <B><FONT COLOR="#0000FF">type</FONT></B><B><FONT COLOR="#228B22"> T.t </FONT></B>=<B><FONT COLOR="#228B22"> S.t
</FONT></B></PRE>
 SML/NJ also allows a definitional structure specification that is similar to a definitional type specification.  For example: 
<pre class=code>
<B><FONT COLOR="#0000FF">structure</FONT></B> S = <B><FONT COLOR="#0000FF">struct</FONT></B> <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> int </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">signature</FONT></B> SIG =
  <B><FONT COLOR="#0000FF">sig</FONT></B>
     <B><FONT COLOR="#0000FF">structure</FONT></B> T : <B><FONT COLOR="#0000FF">sig</FONT></B> <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B> = S
  <B><FONT COLOR="#0000FF">end</FONT></B>
</PRE>
 This is equivalent to the previous examples and to: 
<pre class=code>
<B><FONT COLOR="#0000FF">structure</FONT></B> S = <B><FONT COLOR="#0000FF">struct</FONT></B> <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> int </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B>
<B><FONT COLOR="#0000FF">signature</FONT></B> SIG =
  <B><FONT COLOR="#0000FF">sig</FONT></B>
     <B><FONT COLOR="#0000FF">structure</FONT></B> T : <B><FONT COLOR="#0000FF">sig</FONT></B> <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B> <B><FONT COLOR="#0000FF">where</FONT></B> <B><FONT COLOR="#0000FF">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B>=<B><FONT COLOR="#228B22"> S.t
  </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B>
</PRE>
 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ disallows binding non-datatypes with datatype replication.  For example, it rejects the following program that should be allowed according to the Definition. 
<pre class=code>
<B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> ('a, 'b) t </FONT></B>=<B><FONT COLOR="#228B22"> 'a * 'b
</FONT></B><B><FONT COLOR="#A020F0">datatype</FONT></B><B><FONT COLOR="#228B22"> u </FONT></B>=<B><FONT COLOR="#228B22"> <B><FONT COLOR="#A020F0">datatype</FONT></B> t
</FONT></B></PRE>
 This idiom can be useful when one wants to rename a type without rewriting all the type arguments.  For example, the above would have to be written in SML/NJ as follows. 
<pre class=code>
<B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> ('a, 'b) t </FONT></B>=<B><FONT COLOR="#228B22"> 'a * 'b
</FONT></B><B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> ('a, 'b) u </FONT></B>=<B><FONT COLOR="#228B22"> ('a, 'b) t
</FONT></B></PRE>
 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ disallows sharing a structure with one of its substructures.  For example, SML/NJ disallows the following. 
<pre class=code>
<B><FONT COLOR="#0000FF">signature</FONT></B> SIG =
   <B><FONT COLOR="#0000FF">sig</FONT></B>
      <B><FONT COLOR="#0000FF">structure</FONT></B> S:
         <B><FONT COLOR="#0000FF">sig</FONT></B>
            <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t
            </FONT></B><B><FONT COLOR="#0000FF">structure</FONT></B> T: <B><FONT COLOR="#0000FF">sig</FONT></B> <B><FONT COLOR="#A020F0">type</FONT></B><B><FONT COLOR="#228B22"> t </FONT></B><B><FONT COLOR="#0000FF">end</FONT></B>
         <B><FONT COLOR="#0000FF">end</FONT></B>
      <B><FONT COLOR="#0000FF">sharing</FONT></B> S = S.T
   <B><FONT COLOR="#0000FF">end</FONT></B>
</PRE>
 This signature is allowed by the Definition. 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ disallows polymorphic generalization of refutable patterns. For example, SML/NJ disallows the following. 
<pre class=code>
<B><FONT COLOR="#A020F0">val</FONT></B> [x] = [[]]
<B><FONT COLOR="#A020F0">val</FONT></B> _ = (<B><FONT COLOR="#5F9EA0">1</FONT></B> :: x, <B><FONT COLOR="#BC8F8F">&quot;one&quot;</FONT></B> :: x)
</PRE>
 Recent versions of SML/NJ correctly allow polymorphic generalization of refutable patterns. 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ uses an overly restrictive context for type inference.  For example, SML/NJ rejects both of the following. 
<pre class=code>
<B><FONT COLOR="#0000FF">structure</FONT></B> S =
<B><FONT COLOR="#0000FF">struct</FONT></B>
  <B><FONT COLOR="#A020F0">val</FONT></B> z = (<B><FONT COLOR="#A020F0">fn</FONT></B> x =&gt; x) []
  <B><FONT COLOR="#A020F0">val</FONT></B> y = z :: [true] :: nil
<B><FONT COLOR="#0000FF">end</FONT></B>
</PRE>
 
<pre class=code>
<B><FONT COLOR="#0000FF">structure</FONT></B> S : <B><FONT COLOR="#0000FF">sig</FONT></B> <B><FONT COLOR="#A020F0">val</FONT></B> z : bool list <B><FONT COLOR="#0000FF">end</FONT></B> =
<B><FONT COLOR="#0000FF">struct</FONT></B>
  <B><FONT COLOR="#A020F0">val</FONT></B> z = (<B><FONT COLOR="#A020F0">fn</FONT></B> x =&gt; x) []
<B><FONT COLOR="#0000FF">end</FONT></B>
</PRE>
 These structures are allowed by the Definition. 
</p>
</li>

    </ul>


<h2 id="head-b075a95ec6d7bcb0b6a2ee7dbf5fac2093ba1e54">Deviations from the Basis Library Specification</h2>
<p>
Here are some deviations of SML/NJ from the Basis Library Specification.  
</p>

    <ul>

    <li>
<p>
 SML/NJ exposes the equality of the <tt>vector</tt> type in structures  such as <tt>Word8Vector</tt> that abstractly match <tt>MONO_VECTOR</tt>,  which says <tt>type&nbsp;vector</tt>, not <tt>eqtype&nbsp;vector</tt>.  So, for  example, SML/NJ accepts the following program: 
<pre class=code>
<B><FONT COLOR="#A020F0">fun</FONT></B> f (v: Word8Vector.vector) = v = v
</PRE>
 
</p>
</li>
    <li class="gap">
<p>
 SML/NJ exposes the equality property of the type <tt>status</tt> in <tt>OS.Process</tt>. This means that programs which directly compare two values of type <tt>status</tt> will work with SML/NJ but not MLton. 
</p>
</li>
    <li class="gap">
<p>
 Under SML/NJ on Windows, <tt>OS.Path.validVolume</tt> incorrectly considers absolute empty volumes to be valid. In other words, when the expression 
<pre class=code>
OS.Path.validVolume { isAbs = true, vol = <B><FONT COLOR="#BC8F8F">&quot;&quot;</FONT></B> }
</PRE>
  is evaluated by SML/NJ on Windows, the result is <tt>true</tt>.  MLton, on the other hand, correctly follows the Basis Library Specification, which states that on Windows, <tt>OS.Path.validVolume</tt> should return <tt>false</tt> whenever <tt>isAbs&nbsp;=&nbsp;true</tt> and <tt>vol&nbsp;=&nbsp;""</tt>. 
</p>
 This incorrect behavior causes other <tt>OS.Path</tt> functions to behave differently. For example, when the expression 
<pre class=code>
OS.Path.toString (OS.Path.fromString <B><FONT COLOR="#BC8F8F">&quot;\\usr\\local&quot;</FONT></B>)
</PRE>
<p>
  is evaluated by SML/NJ on Windows, the result is <tt>"\\usr\\local"</tt>, whereas under MLton on Windows, evaluating this expression (correctly) causes an <tt>OS.Path.Path</tt> exception to be raised. 
</p>
</li>
</ul>

</div>



<p>
<hr>
Last edited on 2010-05-20 18:27:00 by <span title="fenrir.cs.rit.edu"><a href="MatthewFluet">MatthewFluet</a></span>.
</body></html>

APT Browse - Built by Thomas Orozco.