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<a href="./Home">MLton 20180207</a>\r
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<div id="header">\r
<h1>MLBasisExamples</h1>\r
</div>\r
<div id="content">\r
<div id="preamble">\r
<div class="sectionbody">\r
<div class="paragraph"><p>Here are some example uses of <a href="MLBasis">ML Basis</a> files.</p></div>\r
</div>\r
</div>\r
<div class="sect1">\r
<h2 id="_complete_program">Complete program</h2>\r
<div class="sectionbody">\r
<div class="paragraph"><p>Suppose your complete program consists of the files <span class="monospaced">file1.sml</span>, &#8230;,\r
<span class="monospaced">filen.sml</span>, which depend upon libraries <span class="monospaced">lib1.mlb</span>, &#8230;, <span class="monospaced">libm.mlb</span>.</p></div>\r
<div class="listingblock">\r
<div class="content monospaced">\r
<pre>(* import libraries *)\r
lib1.mlb\r
...\r
libm.mlb\r
\r
(* program files *)\r
file1.sml\r
...\r
filen.sml</pre>\r
</div></div>\r
<div class="paragraph"><p>The bases denoted by <span class="monospaced">lib1.mlb</span>, &#8230;, <span class="monospaced">libm.mlb</span> are merged (bindings\r
of names in later bases take precedence over bindings of the same name\r
in earlier bases), producing a basis in which <span class="monospaced">file1.sml</span>, &#8230;,\r
<span class="monospaced">filen.sml</span> are elaborated, adding additional bindings to the basis.</p></div>\r
</div>\r
</div>\r
<div class="sect1">\r
<h2 id="_export_filter">Export filter</h2>\r
<div class="sectionbody">\r
<div class="paragraph"><p>Suppose you only want to export certain structures, signatures, and\r
functors from a collection of files.</p></div>\r
<div class="listingblock">\r
<div class="content monospaced">\r
<pre>local\r
  file1.sml\r
  ...\r
  filen.sml\r
in\r
  (* export filter here *)\r
  functor F\r
  structure S\r
end</pre>\r
</div></div>\r
<div class="paragraph"><p>While <span class="monospaced">file1.sml</span>, &#8230;, <span class="monospaced">filen.sml</span> may declare top-level identifiers\r
in addition to <span class="monospaced">F</span> and <span class="monospaced">S</span>, such names are not accessible to programs\r
and libraries that import this <span class="monospaced">.mlb</span>.</p></div>\r
</div>\r
</div>\r
<div class="sect1">\r
<h2 id="_export_filter_with_renaming">Export filter with renaming</h2>\r
<div class="sectionbody">\r
<div class="paragraph"><p>Suppose you want an export filter, but want to rename one of the\r
modules.</p></div>\r
<div class="listingblock">\r
<div class="content monospaced">\r
<pre>local\r
  file1.sml\r
  ...\r
  filen.sml\r
in\r
  (* export filter, with renaming, here *)\r
  functor F\r
  structure S' = S\r
end</pre>\r
</div></div>\r
<div class="paragraph"><p>Note that <span class="monospaced">functor F</span> is an abbreviation for <span class="monospaced">functor F = F</span>, which\r
simply exports an identifier under the same name.</p></div>\r
</div>\r
</div>\r
<div class="sect1">\r
<h2 id="_import_filter">Import filter</h2>\r
<div class="sectionbody">\r
<div class="paragraph"><p>Suppose you only want to import a functor <span class="monospaced">F</span> from one library and a\r
structure <span class="monospaced">S</span> from another library.</p></div>\r
<div class="listingblock">\r
<div class="content monospaced">\r
<pre>local\r
  lib1.mlb\r
in\r
  (* import filter here *)\r
  functor F\r
end\r
local\r
  lib2.mlb\r
in\r
  (* import filter here *)\r
  structure S\r
end\r
file1.sml\r
...\r
filen.sml</pre>\r
</div></div>\r
</div>\r
</div>\r
<div class="sect1">\r
<h2 id="_import_filter_with_renaming">Import filter with renaming</h2>\r
<div class="sectionbody">\r
<div class="paragraph"><p>Suppose you want to import a structure <span class="monospaced">S</span> from one library and\r
another structure <span class="monospaced">S</span> from another library.</p></div>\r
<div class="listingblock">\r
<div class="content monospaced">\r
<pre>local\r
  lib1.mlb\r
in\r
  (* import filter, with renaming, here *)\r
  structure S1 = S\r
end\r
local\r
  lib2.mlb\r
in\r
  (* import filter, with renaming, here *)\r
  structure S2 = S\r
end\r
file1.sml\r
...\r
filen.sml</pre>\r
</div></div>\r
</div>\r
</div>\r
<div class="sect1">\r
<h2 id="_full_basis">Full Basis</h2>\r
<div class="sectionbody">\r
<div class="paragraph"><p>Since the Modules level of SML is the natural means for organizing\r
program and library components, MLB files provide convenient syntax\r
for renaming Modules level identifiers (in fact, renaming of functor\r
identifiers provides a mechanism that is not available in SML).\r
However, please note that <span class="monospaced">.mlb</span> files elaborate to full bases\r
including top-level types and values (including infix status), in\r
addition to structures, signatures, and functors.  For example,\r
suppose you wished to extend the <a href="BasisLibrary">Basis Library</a> with an\r
<span class="monospaced">('a, 'b) either</span> datatype corresponding to a disjoint sum; the type\r
and some operations should be available at the top-level;\r
additionally, a signature and structure provide the complete\r
interface.</p></div>\r
<div class="paragraph"><p>We could use the following files.</p></div>\r
<div class="paragraph"><p><span class="monospaced">either-sigs.sml</span></p></div>\r
<div class="listingblock">\r
<div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">EITHER_GLOBAL</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r
<span class="w">  </span><span class="k">sig</span><span class="w"></span>\r
<span class="w">    </span><span class="k">datatype</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;a</span><span class="p">,</span><span class="w"> </span><span class="n">&#39;b</span><span class="p">)</span><span class="w"> </span><span class="n">either</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Left</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Right</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">&#39;b</span><span class="w"></span>\r
<span class="w">    </span><span class="k">val</span><span class="w"> </span><span class="n">&amp;</span><span class="w">  </span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;a</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;c</span><span class="p">)</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;b</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;c</span><span class="p">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;a</span><span class="p">,</span><span class="w"> </span><span class="n">&#39;b</span><span class="p">)</span><span class="w"> </span><span class="n">either</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;c</span><span class="w"></span>\r
<span class="w">    </span><span class="k">val</span><span class="w"> </span><span class="n">&amp;&amp;</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;a</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;c</span><span class="p">)</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;b</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;d</span><span class="p">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;a</span><span class="p">,</span><span class="w"> </span><span class="n">&#39;b</span><span class="p">)</span><span class="w"> </span><span class="n">either</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;c</span><span class="p">,</span><span class="w"> </span><span class="n">&#39;d</span><span class="p">)</span><span class="w"> </span><span class="n">either</span><span class="w"></span>\r
<span class="w">  </span><span class="k">end</span><span class="w"></span>\r
\r
<span class="k">signature</span><span class="w"> </span><span class="n">EITHER</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r
<span class="w">  </span><span class="k">sig</span><span class="w"></span>\r
<span class="w">    </span><span class="k">include</span><span class="w"> </span><span class="n">EITHER_GLOBAL</span><span class="w"></span>\r
<span class="w">    </span><span class="k">val</span><span class="w"> </span><span class="n">isLeft</span><span class="w">  </span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;a</span><span class="p">,</span><span class="w"> </span><span class="n">&#39;b</span><span class="p">)</span><span class="w"> </span><span class="n">either</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">bool</span><span class="w"></span>\r
<span class="w">    </span><span class="k">val</span><span class="w"> </span><span class="n">isRight</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;a</span><span class="p">,</span><span class="w"> </span><span class="n">&#39;b</span><span class="p">)</span><span class="w"> </span><span class="n">either</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">bool</span><span class="w"></span>\r
<span class="w">    </span><span class="p">...</span><span class="w"></span>\r
<span class="w">  </span><span class="k">end</span><span class="w"></span>\r
</pre></div></div></div>\r
<div class="paragraph"><p><span class="monospaced">either-strs.sml</span></p></div>\r
<div class="listingblock">\r
<div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">Either</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">EITHER</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r
<span class="w">  </span><span class="k">struct</span><span class="w"></span>\r
<span class="w">    </span><span class="k">datatype</span><span class="w"> </span><span class="p">(</span><span class="n">&#39;a</span><span class="p">,</span><span class="w"> </span><span class="n">&#39;b</span><span class="p">)</span><span class="w"> </span><span class="n">either</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Left</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Right</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">&#39;b</span><span class="w"></span>\r
<span class="w">    </span><span class="k">fun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">&amp;</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="k">fn</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"></span>\r
<span class="w">      </span><span class="k">case</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">Left</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Right</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">z</span><span class="w"></span>\r
<span class="w">    </span><span class="k">fun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">&amp;&amp;</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">(</span><span class="n">Left</span><span class="w"> </span><span class="n">o</span><span class="w"> </span><span class="n">f</span><span class="p">)</span><span class="w"> </span><span class="n">&amp;</span><span class="w"> </span><span class="p">(</span><span class="n">Right</span><span class="w"> </span><span class="n">o</span><span class="w"> </span><span class="n">g</span><span class="p">)</span><span class="w"></span>\r
<span class="w">    </span><span class="k">fun</span><span class="w"> </span><span class="n">isLeft</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">((</span><span class="k">fn</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">true</span><span class="p">)</span><span class="w"> </span><span class="n">&amp;</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">false</span><span class="p">))</span><span class="w"> </span><span class="n">x</span><span class="w"></span>\r
<span class="w">    </span><span class="k">fun</span><span class="w"> </span><span class="n">isRight</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">(</span><span class="n">not</span><span class="w"> </span><span class="n">o</span><span class="w"> </span><span class="n">isLeft</span><span class="p">)</span><span class="w"> </span><span class="n">x</span><span class="w"></span>\r
<span class="w">    </span><span class="p">...</span><span class="w"></span>\r
<span class="w">  </span><span class="k">end</span><span class="w"></span>\r
<span class="k">structure</span><span class="w"> </span><span class="n">EitherGlobal</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">EITHER_GLOBAL</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Either</span><span class="w"></span>\r
</pre></div></div></div>\r
<div class="paragraph"><p><span class="monospaced">either-infixes.sml</span></p></div>\r
<div class="listingblock">\r
<div class="content"><div class="highlight"><pre><span class="k">infixr</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="n">&amp;</span><span class="w"> </span><span class="n">&amp;&amp;</span><span class="w"></span>\r
</pre></div></div></div>\r
<div class="paragraph"><p><span class="monospaced">either-open.sml</span></p></div>\r
<div class="listingblock">\r
<div class="content"><div class="highlight"><pre><span class="k">open</span><span class="w"> </span><span class="n">EitherGlobal</span><span class="w"></span>\r
</pre></div></div></div>\r
<div class="paragraph"><p><span class="monospaced">either.mlb</span></p></div>\r
<div class="listingblock">\r
<div class="content monospaced">\r
<pre>either-infixes.sml\r
local\r
  (* import Basis Library *)\r
  $(SML_LIB)/basis/basis.mlb\r
  either-sigs.sml\r
  either-strs.sml\r
in\r
  signature EITHER\r
  structure Either\r
  either-open.sml\r
end</pre>\r
</div></div>\r
<div class="paragraph"><p>A client that imports <span class="monospaced">either.mlb</span> will have access to neither\r
<span class="monospaced">EITHER_GLOBAL</span> nor <span class="monospaced">EitherGlobal</span>, but will have access to the type\r
<span class="monospaced">either</span> and the values <span class="monospaced">&amp;</span> and <span class="monospaced">&amp;&amp;</span> (with infix status) in the\r
top-level environment.  Note that <span class="monospaced">either-infixes.sml</span> is outside the\r
scope of the local, because we want the infixes available in the\r
implementation of the library and to clients of the library.</p></div>\r
</div>\r
</div>\r
</div>\r
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	22	<a href="./Home">MLton 20180207</a>\r
	23	</div>\r
	24	</div>\r
	25	<div id="header">\r
	26	<h1>MLBasisExamples</h1>\r
	27	</div>\r
	28	<div id="content">\r
	29	<div id="preamble">\r
	30	<div class="sectionbody">\r
	31	<div class="paragraph"><p>Here are some example uses of <a href="MLBasis">ML Basis</a> files.</p></div>\r
	32	</div>\r
	33	</div>\r
	34	<div class="sect1">\r
	35	<h2 id="_complete_program">Complete program</h2>\r
	36	<div class="sectionbody">\r
	37	<div class="paragraph"><p>Suppose your complete program consists of the files <span class="monospaced">file1.sml</span>, …,\r
	38	<span class="monospaced">filen.sml</span>, which depend upon libraries <span class="monospaced">lib1.mlb</span>, …, <span class="monospaced">libm.mlb</span>.</p></div>\r
	39	<div class="listingblock">\r
	40	<div class="content monospaced">\r
	41	<pre>(* import libraries *)\r
	42	lib1.mlb\r
	43	...\r
	44	libm.mlb\r
	45	\r
	46	(* program files *)\r
	47	file1.sml\r
	48	...\r
	49	filen.sml</pre>\r
	50	</div></div>\r
	51	<div class="paragraph"><p>The bases denoted by <span class="monospaced">lib1.mlb</span>, …, <span class="monospaced">libm.mlb</span> are merged (bindings\r
	52	of names in later bases take precedence over bindings of the same name\r
	53	in earlier bases), producing a basis in which <span class="monospaced">file1.sml</span>, …,\r
	54	<span class="monospaced">filen.sml</span> are elaborated, adding additional bindings to the basis.</p></div>\r
	55	</div>\r
	56	</div>\r
	57	<div class="sect1">\r
	58	<h2 id="_export_filter">Export filter</h2>\r
	59	<div class="sectionbody">\r
	60	<div class="paragraph"><p>Suppose you only want to export certain structures, signatures, and\r
	61	functors from a collection of files.</p></div>\r
	62	<div class="listingblock">\r
	63	<div class="content monospaced">\r
	64	<pre>local\r
65	file1.sml\r
66	...\r
67	filen.sml\r
68	in\r
69	(* export filter here *)\r
70	functor F\r
71	structure S\r
72	end</pre>\r
73	</div></div>\r
74	<div class="paragraph"><p>While <span class="monospaced">file1.sml</span>, …, <span class="monospaced">filen.sml</span> may declare top-level identifiers\r
75	in addition to <span class="monospaced">F</span> and <span class="monospaced">S</span>, such names are not accessible to programs\r
76	and libraries that import this <span class="monospaced">.mlb</span>.</p></div>\r
77	</div>\r
78	</div>\r
79	<div class="sect1">\r
80	<h2 id="_export_filter_with_renaming">Export filter with renaming</h2>\r
81	<div class="sectionbody">\r
82	<div class="paragraph"><p>Suppose you want an export filter, but want to rename one of the\r
83	modules.</p></div>\r
84	<div class="listingblock">\r
85	<div class="content monospaced">\r
86	<pre>local\r
87	file1.sml\r
88	...\r
89	filen.sml\r
90	in\r
91	(* export filter, with renaming, here *)\r
92	functor F\r
93	structure S' = S\r
94	end</pre>\r
95	</div></div>\r
96	<div class="paragraph"><p>Note that <span class="monospaced">functor F</span> is an abbreviation for <span class="monospaced">functor F = F</span>, which\r
97	simply exports an identifier under the same name.</p></div>\r
98	</div>\r
99	</div>\r
100	<div class="sect1">\r
101	<h2 id="_import_filter">Import filter</h2>\r
102	<div class="sectionbody">\r
103	<div class="paragraph"><p>Suppose you only want to import a functor <span class="monospaced">F</span> from one library and a\r
104	structure <span class="monospaced">S</span> from another library.</p></div>\r
105	<div class="listingblock">\r
106	<div class="content monospaced">\r
107	<pre>local\r
108	lib1.mlb\r
109	in\r
110	(* import filter here *)\r
111	functor F\r
112	end\r
113	local\r
114	lib2.mlb\r
115	in\r
116	(* import filter here *)\r
117	structure S\r
118	end\r
119	file1.sml\r
120	...\r
121	filen.sml</pre>\r
122	</div></div>\r
123	</div>\r
124	</div>\r
125	<div class="sect1">\r
126	<h2 id="_import_filter_with_renaming">Import filter with renaming</h2>\r
127	<div class="sectionbody">\r
128	<div class="paragraph"><p>Suppose you want to import a structure <span class="monospaced">S</span> from one library and\r
129	another structure <span class="monospaced">S</span> from another library.</p></div>\r
130	<div class="listingblock">\r
131	<div class="content monospaced">\r
132	<pre>local\r
133	lib1.mlb\r
134	in\r
135	(* import filter, with renaming, here *)\r
136	structure S1 = S\r
137	end\r
138	local\r
139	lib2.mlb\r
140	in\r
141	(* import filter, with renaming, here *)\r
142	structure S2 = S\r
143	end\r
144	file1.sml\r
145	...\r
146	filen.sml</pre>\r
147	</div></div>\r
148	</div>\r
149	</div>\r
150	<div class="sect1">\r
151	<h2 id="_full_basis">Full Basis</h2>\r
152	<div class="sectionbody">\r
153	<div class="paragraph"><p>Since the Modules level of SML is the natural means for organizing\r
154	program and library components, MLB files provide convenient syntax\r
155	for renaming Modules level identifiers (in fact, renaming of functor\r
156	identifiers provides a mechanism that is not available in SML).\r
157	However, please note that <span class="monospaced">.mlb</span> files elaborate to full bases\r
158	including top-level types and values (including infix status), in\r
159	addition to structures, signatures, and functors. For example,\r
160	suppose you wished to extend the <a href="BasisLibrary">Basis Library</a> with an\r
161	<span class="monospaced">('a, 'b) either</span> datatype corresponding to a disjoint sum; the type\r
162	and some operations should be available at the top-level;\r
163	additionally, a signature and structure provide the complete\r
164	interface.</p></div>\r
165	<div class="paragraph"><p>We could use the following files.</p></div>\r
166	<div class="paragraph"><p><span class="monospaced">either-sigs.sml</span></p></div>\r
167	<div class="listingblock">\r
168	<div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">EITHER_GLOBAL</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r
169	<span class="w"> </span><span class="k">sig</span><span class="w"></span>\r
170	<span class="w"> </span><span class="k">datatype</span><span class="w"> </span><span class="p">(</span><span class="n">'a</span><span class="p">,</span><span class="w"> </span><span class="n">'b</span><span class="p">)</span><span class="w"> </span><span class="n">either</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Left</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">'a</span><span class="w"> </span><span class="p">\|</span><span class="w"> </span><span class="n">Right</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">'b</span><span class="w"></span>\r
171	<span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">&</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">'a</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'c</span><span class="p">)</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="p">(</span><span class="n">'b</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'c</span><span class="p">)</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="p">(</span><span class="n">'a</span><span class="p">,</span><span class="w"> </span><span class="n">'b</span><span class="p">)</span><span class="w"> </span><span class="n">either</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'c</span><span class="w"></span>\r
172	<span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">&&</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">'a</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'c</span><span class="p">)</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="p">(</span><span class="n">'b</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'d</span><span class="p">)</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="p">(</span><span class="n">'a</span><span class="p">,</span><span class="w"> </span><span class="n">'b</span><span class="p">)</span><span class="w"> </span><span class="n">either</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="p">(</span><span class="n">'c</span><span class="p">,</span><span class="w"> </span><span class="n">'d</span><span class="p">)</span><span class="w"> </span><span class="n">either</span><span class="w"></span>\r
173	<span class="w"> </span><span class="k">end</span><span class="w"></span>\r
174	\r
175	<span class="k">signature</span><span class="w"> </span><span class="n">EITHER</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r
176	<span class="w"> </span><span class="k">sig</span><span class="w"></span>\r
177	<span class="w"> </span><span class="k">include</span><span class="w"> </span><span class="n">EITHER_GLOBAL</span><span class="w"></span>\r
178	<span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">isLeft</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">'a</span><span class="p">,</span><span class="w"> </span><span class="n">'b</span><span class="p">)</span><span class="w"> </span><span class="n">either</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">bool</span><span class="w"></span>\r
179	<span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">isRight</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">'a</span><span class="p">,</span><span class="w"> </span><span class="n">'b</span><span class="p">)</span><span class="w"> </span><span class="n">either</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">bool</span><span class="w"></span>\r
180	<span class="w"> </span><span class="p">...</span><span class="w"></span>\r
181	<span class="w"> </span><span class="k">end</span><span class="w"></span>\r
182	</pre></div></div></div>\r
183	<div class="paragraph"><p><span class="monospaced">either-strs.sml</span></p></div>\r
184	<div class="listingblock">\r
185	<div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">Either</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">EITHER</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r
186	<span class="w"> </span><span class="k">struct</span><span class="w"></span>\r
187	<span class="w"> </span><span class="k">datatype</span><span class="w"> </span><span class="p">(</span><span class="n">'a</span><span class="p">,</span><span class="w"> </span><span class="n">'b</span><span class="p">)</span><span class="w"> </span><span class="n">either</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Left</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">'a</span><span class="w"> </span><span class="p">\|</span><span class="w"> </span><span class="n">Right</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">'b</span><span class="w"></span>\r
188	<span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">&</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="k">fn</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=></span><span class="w"></span>\r
189	<span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">Left</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="p">\|</span><span class="w"> </span><span class="n">Right</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">z</span><span class="w"></span>\r
190	<span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">&&</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">(</span><span class="n">Left</span><span class="w"> </span><span class="n">o</span><span class="w"> </span><span class="n">f</span><span class="p">)</span><span class="w"> </span><span class="n">&</span><span class="w"> </span><span class="p">(</span><span class="n">Right</span><span class="w"> </span><span class="n">o</span><span class="w"> </span><span class="n">g</span><span class="p">)</span><span class="w"></span>\r
191	<span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">isLeft</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">((</span><span class="k">fn</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">true</span><span class="p">)</span><span class="w"> </span><span class="n">&</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">false</span><span class="p">))</span><span class="w"> </span><span class="n">x</span><span class="w"></span>\r
192	<span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">isRight</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">(</span><span class="n">not</span><span class="w"> </span><span class="n">o</span><span class="w"> </span><span class="n">isLeft</span><span class="p">)</span><span class="w"> </span><span class="n">x</span><span class="w"></span>\r
193	<span class="w"> </span><span class="p">...</span><span class="w"></span>\r
194	<span class="w"> </span><span class="k">end</span><span class="w"></span>\r
195	<span class="k">structure</span><span class="w"> </span><span class="n">EitherGlobal</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">EITHER_GLOBAL</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Either</span><span class="w"></span>\r
196	</pre></div></div></div>\r
197	<div class="paragraph"><p><span class="monospaced">either-infixes.sml</span></p></div>\r
198	<div class="listingblock">\r
199	<div class="content"><div class="highlight"><pre><span class="k">infixr</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="n">&</span><span class="w"> </span><span class="n">&&</span><span class="w"></span>\r
200	</pre></div></div></div>\r
201	<div class="paragraph"><p><span class="monospaced">either-open.sml</span></p></div>\r
202	<div class="listingblock">\r
203	<div class="content"><div class="highlight"><pre><span class="k">open</span><span class="w"> </span><span class="n">EitherGlobal</span><span class="w"></span>\r
204	</pre></div></div></div>\r
205	<div class="paragraph"><p><span class="monospaced">either.mlb</span></p></div>\r
206	<div class="listingblock">\r
207	<div class="content monospaced">\r
208	<pre>either-infixes.sml\r
209	local\r
210	(* import Basis Library *)\r
211	$(SML_LIB)/basis/basis.mlb\r
212	either-sigs.sml\r
213	either-strs.sml\r
214	in\r
215	signature EITHER\r
216	structure Either\r
217	either-open.sml\r
218	end</pre>\r
219	</div></div>\r
220	<div class="paragraph"><p>A client that imports <span class="monospaced">either.mlb</span> will have access to neither\r
221	<span class="monospaced">EITHER_GLOBAL</span> nor <span class="monospaced">EitherGlobal</span>, but will have access to the type\r
222	<span class="monospaced">either</span> and the values <span class="monospaced">&</span> and <span class="monospaced">&&</span> (with infix status) in the\r
223	top-level environment. Note that <span class="monospaced">either-infixes.sml</span> is outside the\r
224	scope of the local, because we want the infixes available in the\r
225	implementation of the library and to clients of the library.</p></div>\r
226	</div>\r
227	</div>\r
228	</div>\r
229	<div id="footnotes"><hr></div>\r
230	<div id="footer">\r
231	<div id="footer-text">\r
232	</div>\r
233	<div id="footer-badges">\r
234	</div>\r
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236	</body>\r
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