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22 | <a href="./Home">MLton 20180207</a>\r | |
23 | </div>\r | |
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25 | <div id="header">\r | |
26 | <h1>PrintfGentle</h1>\r | |
27 | <div id="toc"> | |
28 | <div id="toctitle">Table of Contents</div> | |
29 | <noscript><p><b>JavaScript must be enabled in your browser to display the table of contents.</b></p></noscript> | |
30 | </div>\r | |
31 | </div>\r | |
32 | <div id="content">\r | |
33 | <div id="preamble">\r | |
34 | <div class="sectionbody">\r | |
35 | <div class="paragraph"><p>This page provides a gentle introduction and derivation of <a href="Printf">Printf</a>,\r | |
36 | with sections and arrangement more suitable to a talk.</p></div>\r | |
37 | </div>\r | |
38 | </div>\r | |
39 | <div class="sect1">\r | |
40 | <h2 id="_introduction">Introduction</h2>\r | |
41 | <div class="sectionbody">\r | |
42 | <div class="paragraph"><p>SML does not have <span class="monospaced">printf</span>. Could we define it ourselves?</p></div>\r | |
43 | <div class="listingblock">\r | |
44 | <div class="content"><div class="highlight"><pre><span class="k">val</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="p">(</span><span class="s">"here's an int %d and a real %f.</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="mi">13</span><span class="p">,</span><span class="w"> </span><span class="mf">17.0</span><span class="p">)</span><span class="w"></span>\r | |
45 | <span class="k">val</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="p">(</span><span class="s">"here's three values (%d, %f, %f).</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span><span class="w"> </span><span class="mi">13</span><span class="p">,</span><span class="w"> </span><span class="mf">17.0</span><span class="p">,</span><span class="w"> </span><span class="mf">19.0</span><span class="p">)</span><span class="w"></span>\r | |
46 | </pre></div></div></div>\r | |
47 | <div class="paragraph"><p>What could the type of <span class="monospaced">printf</span> be?</p></div>\r | |
48 | <div class="paragraph"><p>This obviously can’t work, because SML functions take a fixed number\r | |
49 | of arguments. Actually they take one argument, but if that’s a tuple,\r | |
50 | it can only have a fixed number of components.</p></div>\r | |
51 | </div>\r | |
52 | </div>\r | |
53 | <div class="sect1">\r | |
54 | <h2 id="_from_tupling_to_currying">From tupling to currying</h2>\r | |
55 | <div class="sectionbody">\r | |
56 | <div class="paragraph"><p>What about currying to get around the typing problem?</p></div>\r | |
57 | <div class="listingblock">\r | |
58 | <div class="content"><div class="highlight"><pre><span class="k">val</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="s">"here's an int %d and a real %f.</span><span class="se">\n</span><span class="s">"</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="mf">17.0</span><span class="w"></span>\r | |
59 | <span class="k">val</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="s">"here's three values (%d, %f, %f).</span><span class="se">\n</span><span class="s">"</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="mf">17.0</span><span class="w"> </span><span class="mf">19.0</span><span class="w"></span>\r | |
60 | </pre></div></div></div>\r | |
61 | <div class="paragraph"><p>That fails for a similar reason. We need two types for <span class="monospaced">printf</span>.</p></div>\r | |
62 | <div class="listingblock">\r | |
63 | <div class="content monospaced">\r | |
64 | <pre>val printf: string -> int -> real -> unit\r | |
65 | val printf: string -> int -> real -> real -> unit</pre>\r | |
66 | </div></div>\r | |
67 | <div class="paragraph"><p>This can’t work, because <span class="monospaced">printf</span> can only have one type. SML doesn’t\r | |
68 | support programmer-defined overloading.</p></div>\r | |
69 | </div>\r | |
70 | </div>\r | |
71 | <div class="sect1">\r | |
72 | <h2 id="_overloading_and_dependent_types">Overloading and dependent types</h2>\r | |
73 | <div class="sectionbody">\r | |
74 | <div class="paragraph"><p>Even without worrying about number of arguments, there is another\r | |
75 | problem. The type of <span class="monospaced">printf</span> depends on the format string.</p></div>\r | |
76 | <div class="listingblock">\r | |
77 | <div class="content"><div class="highlight"><pre><span class="k">val</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="s">"here's an int %d and a real %f.</span><span class="se">\n</span><span class="s">"</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="mf">17.0</span><span class="w"></span>\r | |
78 | <span class="k">val</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="s">"here's a real %f and an int %d.</span><span class="se">\n</span><span class="s">"</span><span class="w"> </span><span class="mf">17.0</span><span class="w"> </span><span class="mi">13</span><span class="w"></span>\r | |
79 | </pre></div></div></div>\r | |
80 | <div class="paragraph"><p>Now we need</p></div>\r | |
81 | <div class="listingblock">\r | |
82 | <div class="content monospaced">\r | |
83 | <pre>val printf: string -> int -> real -> unit\r | |
84 | val printf: string -> real -> int -> unit</pre>\r | |
85 | </div></div>\r | |
86 | <div class="paragraph"><p>Again, this can’t possibly working because SML doesn’t have\r | |
87 | overloading, and types can’t depend on values.</p></div>\r | |
88 | </div>\r | |
89 | </div>\r | |
90 | <div class="sect1">\r | |
91 | <h2 id="_idea_express_type_information_in_the_format_string">Idea: express type information in the format string</h2>\r | |
92 | <div class="sectionbody">\r | |
93 | <div class="paragraph"><p>If we express type information in the format string, then different\r | |
94 | uses of <span class="monospaced">printf</span> can have different types.</p></div>\r | |
95 | <div class="listingblock">\r | |
96 | <div class="content"><div class="highlight"><pre><span class="k">type</span><span class="w"> </span><span class="n">'a</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="cm">(* the type of format strings *)</span><span class="w"></span>\r | |
97 | <span class="k">val</span><span class="w"> </span><span class="n">printf</span><span class="p">:</span><span class="w"> </span><span class="n">'a</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'a</span><span class="w"></span>\r | |
98 | <span class="k">infix</span><span class="w"> </span><span class="n">D</span><span class="w"> </span><span class="n">F</span><span class="w"></span>\r | |
99 | <span class="k">val</span><span class="w"> </span><span class="n">fs1</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">int</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">unit</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="s">"here's an int "</span><span class="n">D</span><span class="s">" and a real "</span><span class="n">F</span><span class="s">".</span><span class="se">\n</span><span class="s">"</span><span class="w"></span>\r | |
100 | <span class="k">val</span><span class="w"> </span><span class="n">fs2</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">int</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">unit</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
101 | <span class="w"> </span><span class="s">"here's three values ("</span><span class="n">D</span><span class="s">", "</span><span class="n">F</span><span class="s">", "</span><span class="n">F</span><span class="s">").</span><span class="se">\n</span><span class="s">"</span><span class="w"></span>\r | |
102 | <span class="k">val</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="n">fs1</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="mf">17.0</span><span class="w"></span>\r | |
103 | <span class="k">val</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="n">fs2</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="mf">17.0</span><span class="w"> </span><span class="mf">19.0</span><span class="w"></span>\r | |
104 | </pre></div></div></div>\r | |
105 | <div class="paragraph"><p>Now, our two calls to <span class="monospaced">printf</span> type check, because the format\r | |
106 | string specializes <span class="monospaced">printf</span> to the appropriate type.</p></div>\r | |
107 | </div>\r | |
108 | </div>\r | |
109 | <div class="sect1">\r | |
110 | <h2 id="_the_types_of_format_characters">The types of format characters</h2>\r | |
111 | <div class="sectionbody">\r | |
112 | <div class="paragraph"><p>What should the type of format characters <span class="monospaced">D</span> and <span class="monospaced">F</span> be? Each format\r | |
113 | character requires an additional argument of the appropriate type to\r | |
114 | be supplied to <span class="monospaced">printf</span>.</p></div>\r | |
115 | <div class="paragraph"><p>Idea: guess the final type that will be needed for <span class="monospaced">printf</span> the format\r | |
116 | string and verify it with each format character.</p></div>\r | |
117 | <div class="listingblock">\r | |
118 | <div class="content"><div class="highlight"><pre><span class="k">type</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">t</span><span class="w"> </span><span class="cm">(* 'a = rest of type to verify, 'b = final type *)</span><span class="w"></span>\r | |
119 | <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="n">string</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">'a</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="cm">(* guess the type, which must be verified *)</span><span class="w"></span>\r | |
120 | <span class="k">val</span><span class="w"> </span><span class="n">D</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">int</span><span class="w"> </span><span class="p">-></span><span class="w"> </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">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">string</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">t</span><span class="w"> </span><span class="cm">(* consume an int *)</span><span class="w"></span>\r | |
121 | <span class="k">val</span><span class="w"> </span><span class="n">F</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">real</span><span class="w"> </span><span class="p">-></span><span class="w"> </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">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">string</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">t</span><span class="w"> </span><span class="cm">(* consume a real *)</span><span class="w"></span>\r | |
122 | <span class="k">val</span><span class="w"> </span><span class="n">printf</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">unit</span><span class="p">,</span><span class="w"> </span><span class="n">'a</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'a</span><span class="w"></span>\r | |
123 | </pre></div></div></div>\r | |
124 | <div class="paragraph"><p>Don’t worry. In the end, type inference will guess and verify for us.</p></div>\r | |
125 | </div>\r | |
126 | </div>\r | |
127 | <div class="sect1">\r | |
128 | <h2 id="_understanding_guess_and_verify">Understanding guess and verify</h2>\r | |
129 | <div class="sectionbody">\r | |
130 | <div class="paragraph"><p>Now, let’s build up a format string and a specialized <span class="monospaced">printf</span>.</p></div>\r | |
131 | <div class="listingblock">\r | |
132 | <div class="content"><div class="highlight"><pre><span class="k">infix</span><span class="w"> </span><span class="n">D</span><span class="w"> </span><span class="n">F</span><span class="w"></span>\r | |
133 | <span class="k">val</span><span class="w"> </span><span class="n">f0</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">`</span><span class="s">"here's an int "</span><span class="w"></span>\r | |
134 | <span class="k">val</span><span class="w"> </span><span class="n">f1</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">f0</span><span class="w"> </span><span class="n">D</span><span class="w"> </span><span class="s">" and a real "</span><span class="w"></span>\r | |
135 | <span class="k">val</span><span class="w"> </span><span class="n">f2</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">f1</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="s">".</span><span class="se">\n</span><span class="s">"</span><span class="w"></span>\r | |
136 | <span class="k">val</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="n">f2</span><span class="w"></span>\r | |
137 | </pre></div></div></div>\r | |
138 | <div class="paragraph"><p>These definitions yield the following types.</p></div>\r | |
139 | <div class="listingblock">\r | |
140 | <div class="content"><div class="highlight"><pre><span class="k">val</span><span class="w"> </span><span class="n">f0</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">int</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">unit</span><span class="p">,</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">unit</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
141 | <span class="k">val</span><span class="w"> </span><span class="n">f1</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">real</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">unit</span><span class="p">,</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">unit</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
142 | <span class="k">val</span><span class="w"> </span><span class="n">f2</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">unit</span><span class="p">,</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">unit</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
143 | <span class="k">val</span><span class="w"> </span><span class="n">p</span><span class="p">:</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">unit</span><span class="w"></span>\r | |
144 | </pre></div></div></div>\r | |
145 | <div class="paragraph"><p>So, <span class="monospaced">p</span> is a specialized <span class="monospaced">printf</span> function. We could use it as\r | |
146 | follows</p></div>\r | |
147 | <div class="listingblock">\r | |
148 | <div class="content"><div class="highlight"><pre><span class="k">val</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="mf">17.0</span><span class="w"></span>\r | |
149 | <span class="k">val</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="mi">14</span><span class="w"> </span><span class="mf">19.0</span><span class="w"></span>\r | |
150 | </pre></div></div></div>\r | |
151 | </div>\r | |
152 | </div>\r | |
153 | <div class="sect1">\r | |
154 | <h2 id="_type_checking_this_using_a_functor">Type checking this using a functor</h2>\r | |
155 | <div class="sectionbody">\r | |
156 | <div class="listingblock">\r | |
157 | <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">PRINTF</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
158 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
159 | <span class="w"> </span><span class="k">type</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">t</span><span class="w"></span>\r | |
160 | <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="n">string</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">'a</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
161 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">D</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">int</span><span class="w"> </span><span class="p">-></span><span class="w"> </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">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">string</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">t</span><span class="w"></span>\r | |
162 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">F</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">real</span><span class="w"> </span><span class="p">-></span><span class="w"> </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">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">string</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">t</span><span class="w"></span>\r | |
163 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">printf</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">unit</span><span class="p">,</span><span class="w"> </span><span class="n">'a</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'a</span><span class="w"></span>\r | |
164 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
165 | \r | |
166 | <span class="k">functor</span><span class="w"> </span><span class="n">Test</span><span class="w"> </span><span class="p">(</span><span class="n">P</span><span class="p">:</span><span class="w"> </span><span class="n">PRINTF</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
167 | <span class="w"> </span><span class="k">struct</span><span class="w"></span>\r | |
168 | <span class="w"> </span><span class="k">open</span><span class="w"> </span><span class="n">P</span><span class="w"></span>\r | |
169 | <span class="w"> </span><span class="k">infix</span><span class="w"> </span><span class="n">D</span><span class="w"> </span><span class="n">F</span><span class="w"></span>\r | |
170 | \r | |
171 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="p">(</span><span class="n">`</span><span class="s">"here's an int "</span><span class="n">D</span><span class="s">" and a real "</span><span class="n">F</span><span class="s">".</span><span class="se">\n</span><span class="s">"</span><span class="p">)</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="mf">17.0</span><span class="w"></span>\r | |
172 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="p">(</span><span class="n">`</span><span class="s">"here's three values ("</span><span class="n">D</span><span class="s">", "</span><span class="n">F</span><span class="w"> </span><span class="s">", "</span><span class="n">F</span><span class="s">").</span><span class="se">\n</span><span class="s">"</span><span class="p">)</span><span class="w"> </span><span class="mi">13</span><span class="w"> </span><span class="mf">17.0</span><span class="w"> </span><span class="mf">19.0</span><span class="w"></span>\r | |
173 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
174 | </pre></div></div></div>\r | |
175 | </div>\r | |
176 | </div>\r | |
177 | <div class="sect1">\r | |
178 | <h2 id="_implementing_span_class_monospaced_printf_span">Implementing <span class="monospaced">Printf</span></h2>\r | |
179 | <div class="sectionbody">\r | |
180 | <div class="paragraph"><p>Think of a format character as a formatter transformer. It takes the\r | |
181 | formatter for the part of the format string before it and transforms\r | |
182 | it into a new formatter that first does the left hand bit, then does\r | |
183 | its bit, then continues on with the rest of the format string.</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">Printf</span><span class="p">:</span><span class="w"> </span><span class="n">PRINTF</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">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="p">(</span><span class="n">unit</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'a</span><span class="p">)</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'b</span><span class="w"></span>\r | |
188 | \r | |
189 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="n">f</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">f</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="p">())</span><span class="w"></span>\r | |
190 | \r | |
191 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">`</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="p">(</span><span class="n">print</span><span class="w"> </span><span class="n">s</span><span class="p">;</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="p">()))</span><span class="w"></span>\r | |
192 | \r | |
193 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">D</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
194 | <span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">f</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="k">fn</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="p">=></span><span class="w"></span>\r | |
195 | <span class="w"> </span><span class="p">(</span><span class="n">print</span><span class="w"> </span><span class="p">(</span><span class="n">Int</span><span class="p">.</span><span class="n">toString</span><span class="w"> </span><span class="n">i</span><span class="p">);</span><span class="w"> </span><span class="n">print</span><span class="w"> </span><span class="n">s</span><span class="p">;</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="p">())))</span><span class="w"></span>\r | |
196 | \r | |
197 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
198 | <span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">f</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="k">fn</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="p">=></span><span class="w"></span>\r | |
199 | <span class="w"> </span><span class="p">(</span><span class="n">print</span><span class="w"> </span><span class="p">(</span><span class="n">Real</span><span class="p">.</span><span class="n">toString</span><span class="w"> </span><span class="n">i</span><span class="p">);</span><span class="w"> </span><span class="n">print</span><span class="w"> </span><span class="n">s</span><span class="p">;</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="p">())))</span><span class="w"></span>\r | |
200 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
201 | </pre></div></div></div>\r | |
202 | </div>\r | |
203 | </div>\r | |
204 | <div class="sect1">\r | |
205 | <h2 id="_testing_printf">Testing printf</h2>\r | |
206 | <div class="sectionbody">\r | |
207 | <div class="listingblock">\r | |
208 | <div class="content"><div class="highlight"><pre><span class="k">structure</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">Test</span><span class="w"> </span><span class="p">(</span><span class="n">Printf</span><span class="p">)</span><span class="w"></span>\r | |
209 | </pre></div></div></div>\r | |
210 | </div>\r | |
211 | </div>\r | |
212 | <div class="sect1">\r | |
213 | <h2 id="_user_definable_formats">User-definable formats</h2>\r | |
214 | <div class="sectionbody">\r | |
215 | <div class="paragraph"><p>The definition of the format characters is pretty much the same.\r | |
216 | Within the <span class="monospaced">Printf</span> structure we can define a format character\r | |
217 | generator.</p></div>\r | |
218 | <div class="listingblock">\r | |
219 | <div class="content"><div class="highlight"><pre><span class="k">val</span><span class="w"> </span><span class="n">newFormat</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">string</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="w"> </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">'c</span><span class="p">)</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">string</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="p">(</span><span class="n">'b</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">t</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
220 | <span class="w"> </span><span class="k">fn</span><span class="w"> </span><span class="n">toString</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="k">fn</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">)</span><span class="w"> </span><span class="p">=></span><span class="w"></span>\r | |
221 | <span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">th</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">f</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="k">fn</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="p">(</span><span class="n">print</span><span class="w"> </span><span class="p">(</span><span class="n">toString</span><span class="w"> </span><span class="n">a</span><span class="p">);</span><span class="w"> </span><span class="n">print</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">th</span><span class="w"> </span><span class="p">())))</span><span class="w"></span>\r | |
222 | <span class="k">val</span><span class="w"> </span><span class="n">D</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">z</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">newFormat</span><span class="w"> </span><span class="n">Int</span><span class="p">.</span><span class="n">toString</span><span class="w"> </span><span class="n">z</span><span class="w"></span>\r | |
223 | <span class="k">val</span><span class="w"> </span><span class="n">F</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">z</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">newFormat</span><span class="w"> </span><span class="n">Real</span><span class="p">.</span><span class="n">toString</span><span class="w"> </span><span class="n">z</span><span class="w"></span>\r | |
224 | </pre></div></div></div>\r | |
225 | </div>\r | |
226 | </div>\r | |
227 | <div class="sect1">\r | |
228 | <h2 id="_a_core_span_class_monospaced_printf_span">A core <span class="monospaced">Printf</span></h2>\r | |
229 | <div class="sectionbody">\r | |
230 | <div class="paragraph"><p>We can now have a very small <span class="monospaced">PRINTF</span> signature, and define all\r | |
231 | the format strings externally to the core module.</p></div>\r | |
232 | <div class="listingblock">\r | |
233 | <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">PRINTF</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
234 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
235 | <span class="w"> </span><span class="k">type</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">t</span><span class="w"></span>\r | |
236 | <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="n">string</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">'a</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
237 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">newFormat</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">string</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="w"> </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">'c</span><span class="p">)</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">string</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="p">(</span><span class="n">'b</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">t</span><span class="w"></span>\r | |
238 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">printf</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">unit</span><span class="p">,</span><span class="w"> </span><span class="n">'a</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'a</span><span class="w"></span>\r | |
239 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
240 | \r | |
241 | <span class="k">structure</span><span class="w"> </span><span class="n">Printf</span><span class="p">:</span><span class="w"> </span><span class="n">PRINTF</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
242 | <span class="w"> </span><span class="k">struct</span><span class="w"></span>\r | |
243 | <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">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="p">(</span><span class="n">unit</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'a</span><span class="p">)</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'b</span><span class="w"></span>\r | |
244 | \r | |
245 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="n">f</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">f</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="p">())</span><span class="w"></span>\r | |
246 | \r | |
247 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">`</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="p">(</span><span class="n">print</span><span class="w"> </span><span class="n">s</span><span class="p">;</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="p">()))</span><span class="w"></span>\r | |
248 | \r | |
249 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">newFormat</span><span class="w"> </span><span class="n">toString</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
250 | <span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">th</span><span class="w"> </span><span class="p">=></span><span class="w"></span>\r | |
251 | <span class="w"> </span><span class="n">f</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="k">fn</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="p">=></span><span class="w"></span>\r | |
252 | <span class="w"> </span><span class="p">(</span><span class="n">print</span><span class="w"> </span><span class="p">(</span><span class="n">toString</span><span class="w"> </span><span class="n">a</span><span class="p">)</span><span class="w"></span>\r | |
253 | <span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">print</span><span class="w"> </span><span class="n">s</span><span class="w"></span>\r | |
254 | <span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">th</span><span class="w"> </span><span class="p">())))</span><span class="w"></span>\r | |
255 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
256 | </pre></div></div></div>\r | |
257 | </div>\r | |
258 | </div>\r | |
259 | <div class="sect1">\r | |
260 | <h2 id="_extending_to_fprintf">Extending to fprintf</h2>\r | |
261 | <div class="sectionbody">\r | |
262 | <div class="paragraph"><p>One can implement fprintf by threading the outstream through all the\r | |
263 | transformers.</p></div>\r | |
264 | <div class="listingblock">\r | |
265 | <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">PRINTF</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
266 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
267 | <span class="w"> </span><span class="k">type</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">t</span><span class="w"></span>\r | |
268 | <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="n">string</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">'a</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
269 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">fprintf</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">unit</span><span class="p">,</span><span class="w"> </span><span class="n">'a</span><span class="p">)</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">TextIO</span><span class="p">.</span><span class="n">outstream</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'a</span><span class="w"></span>\r | |
270 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">newFormat</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">string</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="w"> </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">'c</span><span class="p">)</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">string</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="p">(</span><span class="n">'b</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">t</span><span class="w"></span>\r | |
271 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">printf</span><span class="p">:</span><span class="w"> </span><span class="p">(</span><span class="n">unit</span><span class="p">,</span><span class="w"> </span><span class="n">'a</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'a</span><span class="w"></span>\r | |
272 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
273 | \r | |
274 | <span class="k">structure</span><span class="w"> </span><span class="n">Printf</span><span class="p">:</span><span class="w"> </span><span class="n">PRINTF</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
275 | <span class="w"> </span><span class="k">struct</span><span class="w"></span>\r | |
276 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">out</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">TextIO</span><span class="p">.</span><span class="n">outstream</span><span class="w"></span>\r | |
277 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">output</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">TextIO</span><span class="p">.</span><span class="n">output</span><span class="w"></span>\r | |
278 | \r | |
279 | <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">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="p">(</span><span class="n">out</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'a</span><span class="p">)</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">out</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'b</span><span class="w"></span>\r | |
280 | \r | |
281 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">fprintf</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">out</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">f</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="p">())</span><span class="w"> </span><span class="n">out</span><span class="w"></span>\r | |
282 | \r | |
283 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">fprintf</span><span class="w"> </span><span class="p">(</span><span class="n">t</span><span class="p">,</span><span class="w"> </span><span class="n">TextIO</span><span class="p">.</span><span class="n">stdOut</span><span class="p">)</span><span class="w"></span>\r | |
284 | \r | |
285 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">`</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">a</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">out</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="p">(</span><span class="n">output</span><span class="w"> </span><span class="p">(</span><span class="n">out</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">);</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">out</span><span class="p">))</span><span class="w"></span>\r | |
286 | \r | |
287 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">newFormat</span><span class="w"> </span><span class="n">toString</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
288 | <span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="p">=></span><span class="w"></span>\r | |
289 | <span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">out</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">a</span><span class="w"> </span><span class="p">=></span><span class="w"></span>\r | |
290 | <span class="w"> </span><span class="p">(</span><span class="n">output</span><span class="w"> </span><span class="p">(</span><span class="n">out</span><span class="p">,</span><span class="w"> </span><span class="n">toString</span><span class="w"> </span><span class="n">a</span><span class="p">)</span><span class="w"></span>\r | |
291 | <span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">output</span><span class="w"> </span><span class="p">(</span><span class="n">out</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">)</span><span class="w"></span>\r | |
292 | <span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">g</span><span class="w"> </span><span class="n">out</span><span class="p">)))</span><span class="w"></span>\r | |
293 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
294 | </pre></div></div></div>\r | |
295 | </div>\r | |
296 | </div>\r | |
297 | <div class="sect1">\r | |
298 | <h2 id="_notes">Notes</h2>\r | |
299 | <div class="sectionbody">\r | |
300 | <div class="ulist"><ul>\r | |
301 | <li>\r | |
302 | <p>\r | |
303 | Lesson: instead of using dependent types for a function, express the\r | |
304 | the dependency in the type of the argument.\r | |
305 | </p>\r | |
306 | </li>\r | |
307 | <li>\r | |
308 | <p>\r | |
309 | If <span class="monospaced">printf</span> is partially applied, it will do the printing then and\r | |
310 | there. Perhaps this could be fixed with some kind of terminator.\r | |
311 | </p>\r | |
312 | <div class="paragraph"><p>A syntactic or argument terminator is not necessary. A formatter can\r | |
313 | either be eager (as above) or lazy (as below). A lazy formatter\r | |
314 | accumulates enough state to print the entire string. The simplest\r | |
315 | lazy formatter concatenates the strings as they become available:</p></div>\r | |
316 | <div class="listingblock">\r | |
317 | <div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">PrintfLazyConcat</span><span class="p">:</span><span class="w"> </span><span class="n">PRINTF</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
318 | <span class="w"> </span><span class="k">struct</span><span class="w"></span>\r | |
319 | <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">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="p">(</span><span class="n">string</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'a</span><span class="p">)</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">string</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'b</span><span class="w"></span>\r | |
320 | \r | |
321 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="n">f</span><span class="p">)</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">print</span><span class="w"> </span><span class="s">""</span><span class="w"></span>\r | |
322 | \r | |
323 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">`</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">th</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">s'</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">th</span><span class="w"> </span><span class="p">(</span><span class="n">s'</span><span class="w"> </span><span class="n">^</span><span class="w"> </span><span class="n">s</span><span class="p">))</span><span class="w"></span>\r | |
324 | \r | |
325 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">newFormat</span><span class="w"> </span><span class="n">toString</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
326 | <span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">th</span><span class="w"> </span><span class="p">=></span><span class="w"></span>\r | |
327 | <span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">s'</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">a</span><span class="w"> </span><span class="p">=></span><span class="w"></span>\r | |
328 | <span class="w"> </span><span class="n">th</span><span class="w"> </span><span class="p">(</span><span class="n">s'</span><span class="w"> </span><span class="n">^</span><span class="w"> </span><span class="n">toString</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="n">^</span><span class="w"> </span><span class="n">s</span><span class="p">)))</span><span class="w"></span>\r | |
329 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
330 | </pre></div></div></div>\r | |
331 | <div class="paragraph"><p>It is somewhat more efficient to accumulate the strings as a list:</p></div>\r | |
332 | <div class="listingblock">\r | |
333 | <div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">PrintfLazyList</span><span class="p">:</span><span class="w"> </span><span class="n">PRINTF</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
334 | <span class="w"> </span><span class="k">struct</span><span class="w"></span>\r | |
335 | <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">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="p">(</span><span class="n">string</span><span class="w"> </span><span class="n">list</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'a</span><span class="p">)</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">string</span><span class="w"> </span><span class="n">list</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">'b</span><span class="w"></span>\r | |
336 | \r | |
337 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">printf</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="n">f</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="p">(</span><span class="n">List</span><span class="p">.</span><span class="n">app</span><span class="w"> </span><span class="n">print</span><span class="w"> </span><span class="n">o</span><span class="w"> </span><span class="n">List</span><span class="p">.</span><span class="n">rev</span><span class="p">)</span><span class="w"> </span><span class="p">[]</span><span class="w"></span>\r | |
338 | \r | |
339 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">`</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">th</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">ss</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">th</span><span class="w"> </span><span class="p">(</span><span class="n">s::ss</span><span class="p">))</span><span class="w"></span>\r | |
340 | \r | |
341 | <span class="w"> </span><span class="k">fun</span><span class="w"> </span><span class="n">newFormat</span><span class="w"> </span><span class="n">toString</span><span class="w"> </span><span class="p">(</span><span class="n">T</span><span class="w"> </span><span class="n">f</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
342 | <span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">th</span><span class="w"> </span><span class="p">=></span><span class="w"></span>\r | |
343 | <span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">ss</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">a</span><span class="w"> </span><span class="p">=></span><span class="w"></span>\r | |
344 | <span class="w"> </span><span class="n">th</span><span class="w"> </span><span class="p">(</span><span class="n">s::toString</span><span class="w"> </span><span class="n">a::ss</span><span class="p">)))</span><span class="w"></span>\r | |
345 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
346 | </pre></div></div></div>\r | |
347 | </li>\r | |
348 | </ul></div>\r | |
349 | </div>\r | |
350 | </div>\r | |
351 | <div class="sect1">\r | |
352 | <h2 id="_also_see">Also see</h2>\r | |
353 | <div class="sectionbody">\r | |
354 | <div class="ulist"><ul>\r | |
355 | <li>\r | |
356 | <p>\r | |
357 | <a href="Printf">Printf</a>\r | |
358 | </p>\r | |
359 | </li>\r | |
360 | <li>\r | |
361 | <p>\r | |
362 | <a href="References#Danvy98"> Functional Unparsing</a>\r | |
363 | </p>\r | |
364 | </li>\r | |
365 | </ul></div>\r | |
366 | </div>\r | |
367 | </div>\r | |
368 | </div>\r | |
369 | <div id="footnotes"><hr></div>\r | |
370 | <div id="footer">\r | |
371 | <div id="footer-text">\r | |
372 | </div>\r | |
373 | <div id="footer-badges">\r | |
374 | </div>\r | |
375 | </div>\r | |
376 | </body>\r | |
377 | </html>\r |