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26 <h1>MLBasisExamples</h1>
30 <div class="sectionbody">
31 <div class="paragraph"><p>Here are some example uses of <a href="MLBasis">ML Basis</a> files.</p></div>
35 <h2 id="_complete_program">Complete program</h2>
36 <div class="sectionbody">
37 <div class="paragraph"><p>Suppose your complete program consists of the files <span class="monospaced">file1.sml</span>, …,
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>
39 <div class="listingblock">
40 <div class="content monospaced">
41 <pre>(* import libraries *)
51 <div class="paragraph"><p>The bases denoted by <span class="monospaced">lib1.mlb</span>, …, <span class="monospaced">libm.mlb</span> are merged (bindings
52 of names in later bases take precedence over bindings of the same name
53 in earlier bases), producing a basis in which <span class="monospaced">file1.sml</span>, …,
54 <span class="monospaced">filen.sml</span> are elaborated, adding additional bindings to the basis.</p></div>
58 <h2 id="_export_filter">Export filter</h2>
59 <div class="sectionbody">
60 <div class="paragraph"><p>Suppose you only want to export certain structures, signatures, and
61 functors from a collection of files.</p></div>
62 <div class="listingblock">
63 <div class="content monospaced">
69 (* export filter here *)
74 <div class="paragraph"><p>While <span class="monospaced">file1.sml</span>, …, <span class="monospaced">filen.sml</span> may declare top-level identifiers
75 in addition to <span class="monospaced">F</span> and <span class="monospaced">S</span>, such names are not accessible to programs
76 and libraries that import this <span class="monospaced">.mlb</span>.</p></div>
80 <h2 id="_export_filter_with_renaming">Export filter with renaming</h2>
81 <div class="sectionbody">
82 <div class="paragraph"><p>Suppose you want an export filter, but want to rename one of the
84 <div class="listingblock">
85 <div class="content monospaced">
91 (* export filter, with renaming, here *)
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
97 simply exports an identifier under the same name.</p></div>
101 <h2 id="_import_filter">Import filter</h2>
102 <div class="sectionbody">
103 <div class="paragraph"><p>Suppose you only want to import a functor <span class="monospaced">F</span> from one library and a
104 structure <span class="monospaced">S</span> from another library.</p></div>
105 <div class="listingblock">
106 <div class="content monospaced">
110 (* import filter here *)
116 (* import filter here *)
126 <h2 id="_import_filter_with_renaming">Import filter with renaming</h2>
127 <div class="sectionbody">
128 <div class="paragraph"><p>Suppose you want to import a structure <span class="monospaced">S</span> from one library and
129 another structure <span class="monospaced">S</span> from another library.</p></div>
130 <div class="listingblock">
131 <div class="content monospaced">
135 (* import filter, with renaming, here *)
141 (* import filter, with renaming, here *)
151 <h2 id="_full_basis">Full Basis</h2>
152 <div class="sectionbody">
153 <div class="paragraph"><p>Since the Modules level of SML is the natural means for organizing
154 program and library components, MLB files provide convenient syntax
155 for renaming Modules level identifiers (in fact, renaming of functor
156 identifiers provides a mechanism that is not available in SML).
157 However, please note that <span class="monospaced">.mlb</span> files elaborate to full bases
158 including top-level types and values (including infix status), in
159 addition to structures, signatures, and functors. For example,
160 suppose you wished to extend the <a href="BasisLibrary">Basis Library</a> with an
161 <span class="monospaced">('a, 'b) either</span> datatype corresponding to a disjoint sum; the type
162 and some operations should be available at the top-level;
163 additionally, a signature and structure provide the complete
165 <div class="paragraph"><p>We could use the following files.</p></div>
166 <div class="paragraph"><p><span class="monospaced">either-sigs.sml</span></p></div>
167 <div class="listingblock">
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>
169 <span class="w"> </span><span class="k">sig</span><span class="w"></span>
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>
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>
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>
173 <span class="w"> </span><span class="k">end</span><span class="w"></span>
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>
176 <span class="w"> </span><span class="k">sig</span><span class="w"></span>
177 <span class="w"> </span><span class="k">include</span><span class="w"> </span><span class="n">EITHER_GLOBAL</span><span class="w"></span>
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>
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>
180 <span class="w"> </span><span class="p">...</span><span class="w"></span>
181 <span class="w"> </span><span class="k">end</span><span class="w"></span>
182 </pre></div></div></div>
183 <div class="paragraph"><p><span class="monospaced">either-strs.sml</span></p></div>
184 <div class="listingblock">
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>
186 <span class="w"> </span><span class="k">struct</span><span class="w"></span>
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>
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>
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>
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>
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>
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>
193 <span class="w"> </span><span class="p">...</span><span class="w"></span>
194 <span class="w"> </span><span class="k">end</span><span class="w"></span>
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>
196 </pre></div></div></div>
197 <div class="paragraph"><p><span class="monospaced">either-infixes.sml</span></p></div>
198 <div class="listingblock">
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>
200 </pre></div></div></div>
201 <div class="paragraph"><p><span class="monospaced">either-open.sml</span></p></div>
202 <div class="listingblock">
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>
204 </pre></div></div></div>
205 <div class="paragraph"><p><span class="monospaced">either.mlb</span></p></div>
206 <div class="listingblock">
207 <div class="content monospaced">
208 <pre>either-infixes.sml
210 (* import Basis Library *)
211 $(SML_LIB)/basis/basis.mlb
220 <div class="paragraph"><p>A client that imports <span class="monospaced">either.mlb</span> will have access to neither
221 <span class="monospaced">EITHER_GLOBAL</span> nor <span class="monospaced">EitherGlobal</span>, but will have access to the type
222 <span class="monospaced">either</span> and the values <span class="monospaced">&</span> and <span class="monospaced">&&</span> (with infix status) in the
223 top-level environment. Note that <span class="monospaced">either-infixes.sml</span> is outside the
224 scope of the local, because we want the infixes available in the
225 implementation of the library and to clients of the library.</p></div>
229 <div id="footnotes"><hr></div>
231 <div id="footer-text">
233 <div id="footer-badges">