HCoop / hcoop / debian / mlton.git / blame
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| 6 | <title>Overloading</title>\r | |
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| 19 | <body class="article">\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>Overloading</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>In <a href="StandardML">Standard ML</a>, constants (like <span class="monospaced">13</span>, <span class="monospaced">0w13</span>, <span class="monospaced">13.0</span>)\r | |
| 32 | are overloaded, meaning that they can denote a constant of the\r | |
| 33 | appropriate type as determined by context. SML defines the\r | |
| 34 | overloading classes <em>Int</em>, <em>Real</em>, and <em>Word</em>, which denote the sets\r | |
| 35 | of types that integer, real, and word constants may take on. In\r | |
| 36 | MLton, these are defined as follows.</p></div>\r | |
| 37 | <table class="tableblock frame-all grid-all"\r | |
| 38 | style="\r | |
| 39 | width:100%;\r | |
| 40 | ">\r | |
| 41 | <col style="width:25%;">\r | |
| 42 | <col style="width:75%;">\r | |
| 43 | <tbody>\r | |
| 44 | <tr>\r | |
| 45 | <td class="tableblock halign-center valign-top" ><p class="tableblock"><em>Int</em></p></td>\r | |
| 46 | <td class="tableblock halign-left valign-top" ><p class="tableblock"><span class="monospaced">Int2.int</span>, <span class="monospaced">Int3.int</span>, … <span class="monospaced">Int32.int</span>, <span class="monospaced">Int64.int</span>, <span class="monospaced">Int.int</span>, <span class="monospaced">IntInf.int</span>, <span class="monospaced">LargeInt.int</span>, <span class="monospaced">FixedInt.int</span>, <span class="monospaced">Position.int</span></p></td>\r | |
| 47 | </tr>\r | |
| 48 | <tr>\r | |
| 49 | <td class="tableblock halign-center valign-top" ><p class="tableblock"><em>Real</em></p></td>\r | |
| 50 | <td class="tableblock halign-left valign-top" ><p class="tableblock"><span class="monospaced">Real32.real</span>, <span class="monospaced">Real64.real</span>, <span class="monospaced">Real.real</span>, <span class="monospaced">LargeReal.real</span></p></td>\r | |
| 51 | </tr>\r | |
| 52 | <tr>\r | |
| 53 | <td class="tableblock halign-center valign-top" ><p class="tableblock"><em>Word</em></p></td>\r | |
| 54 | <td class="tableblock halign-left valign-top" ><p class="tableblock"><span class="monospaced">Word2.word</span>, <span class="monospaced">Word3.word</span>, … <span class="monospaced">Word32.word</span>, <span class="monospaced">Word64.word</span>, <span class="monospaced">Word.word</span>, <span class="monospaced">LargeWord.word</span>, <span class="monospaced">SysWord.word</span></p></td>\r | |
| 55 | </tr>\r | |
| 56 | </tbody>\r | |
| 57 | </table>\r | |
| 58 | <div class="paragraph"><p>The <a href="DefinitionOfStandardML">Definition</a> allows flexibility in how\r | |
| 59 | much context is used to resolve overloading. It says that the context\r | |
| 60 | is <em>no larger than the smallest enclosing structure-level\r | |
| 61 | declaration</em>, but that <em>an implementation may require that a smaller\r | |
| 62 | context determines the type</em>. MLton uses the largest possible context\r | |
| 63 | allowed by SML in resolving overloading. If the type of a constant is\r | |
| 64 | not determined by context, then it takes on a default type. In MLton,\r | |
| 65 | these are defined as follows.</p></div>\r | |
| 66 | <table class="tableblock frame-all grid-all"\r | |
| 67 | style="\r | |
| 68 | width:100%;\r | |
| 69 | ">\r | |
| 70 | <col style="width:25%;">\r | |
| 71 | <col style="width:75%;">\r | |
| 72 | <tbody>\r | |
| 73 | <tr>\r | |
| 74 | <td class="tableblock halign-center valign-top" ><p class="tableblock"><em>Int</em></p></td>\r | |
| 75 | <td class="tableblock halign-left valign-top" ><p class="tableblock"><span class="monospaced">Int.int</span></p></td>\r | |
| 76 | </tr>\r | |
| 77 | <tr>\r | |
| 78 | <td class="tableblock halign-center valign-top" ><p class="tableblock"><em>Real</em></p></td>\r | |
| 79 | <td class="tableblock halign-left valign-top" ><p class="tableblock"><span class="monospaced">Real.real</span></p></td>\r | |
| 80 | </tr>\r | |
| 81 | <tr>\r | |
| 82 | <td class="tableblock halign-center valign-top" ><p class="tableblock"><em>Word</em></p></td>\r | |
| 83 | <td class="tableblock halign-left valign-top" ><p class="tableblock"><span class="monospaced">Word.word</span></p></td>\r | |
| 84 | </tr>\r | |
| 85 | </tbody>\r | |
| 86 | </table>\r | |
| 87 | <div class="paragraph"><p>Other implementations may use a smaller context or different default\r | |
| 88 | types.</p></div>\r | |
| 89 | </div>\r | |
| 90 | </div>\r | |
| 91 | <div class="sect1">\r | |
| 92 | <h2 id="_also_see">Also see</h2>\r | |
| 93 | <div class="sectionbody">\r | |
| 94 | <div class="ulist"><ul>\r | |
| 95 | <li>\r | |
| 96 | <p>\r | |
| 97 | <a href="http://www.standardml.org/Basis/top-level-chapter.html">discussion of overloading in the Basis Library</a>\r | |
| 98 | </p>\r | |
| 99 | </li>\r | |
| 100 | </ul></div>\r | |
| 101 | </div>\r | |
| 102 | </div>\r | |
| 103 | <div class="sect1">\r | |
| 104 | <h2 id="_examples">Examples</h2>\r | |
| 105 | <div class="sectionbody">\r | |
| 106 | <div class="ulist"><ul>\r | |
| 107 | <li>\r | |
| 108 | <p>\r | |
| 109 | The following program is rejected.\r | |
| 110 | </p>\r | |
| 111 | <div class="listingblock">\r | |
| 112 | <div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">S</span><span class="p">:</span><span class="w"></span>\r | |
| 113 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
| 114 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="p">:</span><span class="w"> </span><span class="n">Word8</span><span class="p">.</span><span class="n">word</span><span class="w"></span>\r | |
| 115 | <span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
| 116 | <span class="w"> </span><span class="k">struct</span><span class="w"></span>\r | |
| 117 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">0w0</span><span class="w"></span>\r | |
| 118 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
| 119 | </pre></div></div></div>\r | |
| 120 | <div class="paragraph"><p>The smallest enclosing structure declaration for <span class="monospaced">0w0</span> is\r | |
| 121 | <span class="monospaced">val x = 0w0</span>. Hence, <span class="monospaced">0w0</span> receives the default type for words,\r | |
| 122 | which is <span class="monospaced">Word.word</span>.</p></div>\r | |
| 123 | </li>\r | |
| 124 | </ul></div>\r | |
| 125 | </div>\r | |
| 126 | </div>\r | |
| 127 | </div>\r | |
| 128 | <div id="footnotes"><hr></div>\r | |
| 129 | <div id="footer">\r | |
| 130 | <div id="footer-text">\r | |
| 131 | </div>\r | |
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| 133 | </div>\r | |
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| 135 | </body>\r | |
| 136 | </html>\r |