HCoop / hcoop / debian / mlton.git / blame
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1 | <!DOCTYPE html>\r |
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| 5 | <meta name="generator" content="AsciiDoc 8.6.9">\r | |
| 6 | <title>AST</title>\r | |
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| 18 | </head>\r | |
| 19 | <body class="article">\r | |
| 20 | <div id="banner">\r | |
| 21 | <div id="banner-home">\r | |
| 22 | <a href="./Home">MLton 20180207</a>\r | |
| 23 | </div>\r | |
| 24 | </div>\r | |
| 25 | <div id="header">\r | |
| 26 | <h1>AST</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><a href="AST">AST</a> is the <a href="IntermediateLanguage">IntermediateLanguage</a> produced by the <a href="FrontEnd">FrontEnd</a>\r | |
| 32 | and translated by <a href="Elaborate">Elaborate</a> to <a href="CoreML">CoreML</a>.</p></div>\r | |
| 33 | </div>\r | |
| 34 | </div>\r | |
| 35 | <div class="sect1">\r | |
| 36 | <h2 id="_description">Description</h2>\r | |
| 37 | <div class="sectionbody">\r | |
| 38 | <div class="paragraph"><p>The abstract syntax tree produced by the <a href="FrontEnd">FrontEnd</a>.</p></div>\r | |
| 39 | </div>\r | |
| 40 | </div>\r | |
| 41 | <div class="sect1">\r | |
| 42 | <h2 id="_implementation">Implementation</h2>\r | |
| 43 | <div class="sectionbody">\r | |
| 44 | <div class="ulist"><ul>\r | |
| 45 | <li>\r | |
| 46 | <p>\r | |
| 47 | <a href="https://github.com/MLton/mlton/blob/master/mlton/ast/ast-programs.sig"><span class="monospaced">ast-programs.sig</span></a>\r | |
| 48 | </p>\r | |
| 49 | </li>\r | |
| 50 | <li>\r | |
| 51 | <p>\r | |
| 52 | <a href="https://github.com/MLton/mlton/blob/master/mlton/ast/ast-programs.fun"><span class="monospaced">ast-programs.fun</span></a>\r | |
| 53 | </p>\r | |
| 54 | </li>\r | |
| 55 | <li>\r | |
| 56 | <p>\r | |
| 57 | <a href="https://github.com/MLton/mlton/blob/master/mlton/ast/ast-modules.sig"><span class="monospaced">ast-modules.sig</span></a>\r | |
| 58 | </p>\r | |
| 59 | </li>\r | |
| 60 | <li>\r | |
| 61 | <p>\r | |
| 62 | <a href="https://github.com/MLton/mlton/blob/master/mlton/ast/ast-modules.fun"><span class="monospaced">ast-modules.fun</span></a>\r | |
| 63 | </p>\r | |
| 64 | </li>\r | |
| 65 | <li>\r | |
| 66 | <p>\r | |
| 67 | <a href="https://github.com/MLton/mlton/blob/master/mlton/ast/ast-core.sig"><span class="monospaced">ast-core.sig</span></a>\r | |
| 68 | </p>\r | |
| 69 | </li>\r | |
| 70 | <li>\r | |
| 71 | <p>\r | |
| 72 | <a href="https://github.com/MLton/mlton/blob/master/mlton/ast/ast-core.fun"><span class="monospaced">ast-core.fun</span></a>\r | |
| 73 | </p>\r | |
| 74 | </li>\r | |
| 75 | <li>\r | |
| 76 | <p>\r | |
| 77 | <a href="https://github.com/MLton/mlton/tree/master/mlton/ast"><span class="monospaced">ast</span></a>\r | |
| 78 | </p>\r | |
| 79 | </li>\r | |
| 80 | </ul></div>\r | |
| 81 | </div>\r | |
| 82 | </div>\r | |
| 83 | <div class="sect1">\r | |
| 84 | <h2 id="_type_checking">Type Checking</h2>\r | |
| 85 | <div class="sectionbody">\r | |
| 86 | <div class="paragraph"><p>The <a href="AST">AST</a> <a href="IntermediateLanguage">IntermediateLanguage</a> has no independent type\r | |
| 87 | checker. Type inference is performed on an AST program as part of\r | |
| 88 | <a href="Elaborate">Elaborate</a>.</p></div>\r | |
| 89 | </div>\r | |
| 90 | </div>\r | |
| 91 | <div class="sect1">\r | |
| 92 | <h2 id="_details_and_notes">Details and Notes</h2>\r | |
| 93 | <div class="sectionbody">\r | |
| 94 | <div class="sect2">\r | |
| 95 | <h3 id="_source_locations">Source locations</h3>\r | |
| 96 | <div class="paragraph"><p>MLton makes use of a relatively clean method for annotating the\r | |
| 97 | abstract syntax tree with source location information. Every source\r | |
| 98 | program phrase is "wrapped" with the <span class="monospaced">WRAPPED</span> interface:</p></div>\r | |
| 99 | <div class="listingblock">\r | |
| 100 | <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">WRAPPED</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
| 101 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
| 102 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">node'</span><span class="w"></span>\r | |
| 103 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">obj</span><span class="w"></span>\r | |
| 104 | \r | |
| 105 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">dest</span><span class="p">:</span><span class="w"> </span><span class="n">obj</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">node'</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">Region</span><span class="p">.</span><span class="n">t</span><span class="w"></span>\r | |
| 106 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">makeRegion'</span><span class="p">:</span><span class="w"> </span><span class="n">node'</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">SourcePos</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">SourcePos</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">obj</span><span class="w"></span>\r | |
| 107 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">makeRegion</span><span class="p">:</span><span class="w"> </span><span class="n">node'</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">Region</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">obj</span><span class="w"></span>\r | |
| 108 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">node</span><span class="p">:</span><span class="w"> </span><span class="n">obj</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">node'</span><span class="w"></span>\r | |
| 109 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">region</span><span class="p">:</span><span class="w"> </span><span class="n">obj</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">Region</span><span class="p">.</span><span class="n">t</span><span class="w"></span>\r | |
| 110 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
| 111 | </pre></div></div></div>\r | |
| 112 | <div class="paragraph"><p>The key idea is that <span class="monospaced">node'</span> is the type of an unannotated syntax\r | |
| 113 | phrase and <span class="monospaced">obj</span> is the type of its annotated counterpart. In the\r | |
| 114 | implementation, every <span class="monospaced">node'</span> is annotated with a <span class="monospaced">Region.t</span>\r | |
| 115 | (<a href="https://github.com/MLton/mlton/blob/master/mlton/control/region.sig"><span class="monospaced">region.sig</span></a>,\r | |
| 116 | <a href="https://github.com/MLton/mlton/blob/master/mlton/control/region.sml"><span class="monospaced">region.sml</span></a>), which describes the\r | |
| 117 | syntax phrase’s left source position and right source position, where\r | |
| 118 | <span class="monospaced">SourcePos.t</span> (<a href="https://github.com/MLton/mlton/blob/master/mlton/control/source-pos.sig"><span class="monospaced">source-pos.sig</span></a>,\r | |
| 119 | <a href="https://github.com/MLton/mlton/blob/master/mlton/control/source-pos.sml"><span class="monospaced">source-pos.sml</span></a>) denotes a\r | |
| 120 | particular file, line, and column. A typical use of the <span class="monospaced">WRAPPED</span>\r | |
| 121 | interface is illustrated by the following code:</p></div>\r | |
| 122 | <div class="listingblock">\r | |
| 123 | <div class="content"><div class="highlight"><pre><span class="w"> </span><span class="k">datatype</span><span class="w"> </span><span class="n">node</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
| 124 | <span class="w"> </span><span class="n">App</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">Longcon</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
| 125 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Const</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">Const</span><span class="p">.</span><span class="n">t</span><span class="w"></span>\r | |
| 126 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Constraint</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span><span class="n">t</span><span class="w"></span>\r | |
| 127 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">FlatApp</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">vector</span><span class="w"></span>\r | |
| 128 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Layered</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="p">{</span><span class="n">constraint</span><span class="p">:</span><span class="w"> </span><span class="n">Type</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="n">option</span><span class="p">,</span><span class="w"></span>\r | |
| 129 | <span class="w"> </span><span class="n">fixop</span><span class="p">:</span><span class="w"> </span><span class="n">Fixop</span><span class="p">.</span><span class="n">t</span><span class="p">,</span><span class="w"></span>\r | |
| 130 | <span class="w"> </span><span class="n">pat</span><span class="p">:</span><span class="w"> </span><span class="n">t</span><span class="p">,</span><span class="w"></span>\r | |
| 131 | <span class="w"> </span><span class="n">var</span><span class="p">:</span><span class="w"> </span><span class="n">Var</span><span class="p">.</span><span class="n">t</span><span class="p">}</span><span class="w"></span>\r | |
| 132 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">List</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">vector</span><span class="w"></span>\r | |
| 133 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Paren</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
| 134 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Or</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">vector</span><span class="w"></span>\r | |
| 135 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Record</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="p">{</span><span class="n">flexible</span><span class="p">:</span><span class="w"> </span><span class="n">bool</span><span class="p">,</span><span class="w"></span>\r | |
| 136 | <span class="w"> </span><span class="n">items</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">Record</span><span class="p">.</span><span class="n">Field</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">Region</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">Item</span><span class="p">.</span><span class="n">t</span><span class="p">)</span><span class="w"> </span><span class="n">vector</span><span class="p">}</span><span class="w"></span>\r | |
| 137 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Tuple</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">vector</span><span class="w"></span>\r | |
| 138 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Var</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="p">{</span><span class="n">fixop</span><span class="p">:</span><span class="w"> </span><span class="n">Fixop</span><span class="p">.</span><span class="n">t</span><span class="p">,</span><span class="w"></span>\r | |
| 139 | <span class="w"> </span><span class="n">name</span><span class="p">:</span><span class="w"> </span><span class="n">Longvid</span><span class="p">.</span><span class="n">t</span><span class="p">}</span><span class="w"></span>\r | |
| 140 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Vector</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">vector</span><span class="w"></span>\r | |
| 141 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Wild</span><span class="w"></span>\r | |
| 142 | </pre></div></div></div>\r | |
| 143 | <div class="paragraph"><p>Thus, AST nodes are cleanly separated from source locations. By way\r | |
| 144 | of contrast, consider the approach taken by <a href="SMLNJ">SML/NJ</a> (and also\r | |
| 145 | by the <a href="CKitLibrary">CKit Library</a>). Each datatype denoting a syntax\r | |
| 146 | phrase dedicates a special constructor for annotating source\r | |
| 147 | locations:</p></div>\r | |
| 148 | <div class="listingblock">\r | |
| 149 | <div class="content"><div class="highlight"><pre><span class="k">datatype</span><span class="w"> </span><span class="n">pat</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">WildPat</span><span class="w"> </span><span class="cm">(* empty pattern *)</span><span class="w"></span>\r | |
| 150 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">AppPat</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="p">{</span><span class="n">constr</span><span class="p">:</span><span class="n">pat</span><span class="p">,</span><span class="n">argument</span><span class="p">:</span><span class="n">pat</span><span class="p">}</span><span class="w"> </span><span class="cm">(* application *)</span><span class="w"></span>\r | |
| 151 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">MarkPat</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">pat</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">region</span><span class="w"> </span><span class="cm">(* mark a pattern *)</span><span class="w"></span>\r | |
| 152 | </pre></div></div></div>\r | |
| 153 | <div class="paragraph"><p>The main drawback of this approach is that static type checking is not\r | |
| 154 | sufficient to guarantee that the AST emitted from the front-end is\r | |
| 155 | properly annotated.</p></div>\r | |
| 156 | </div>\r | |
| 157 | </div>\r | |
| 158 | </div>\r | |
| 159 | </div>\r | |
| 160 | <div id="footnotes"><hr></div>\r | |
| 161 | <div id="footer">\r | |
| 162 | <div id="footer-text">\r | |
| 163 | </div>\r | |
| 164 | <div id="footer-badges">\r | |
| 165 | </div>\r | |
| 166 | </div>\r | |
| 167 | </body>\r | |
| 168 | </html>\r |