/usr/share/doc/frown-doc/html/Manual005.html is in frown-doc 0.6.1-14.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 | <!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta name="generator" content="hevea 2.06">
<link rel="stylesheet" type="text/css" href="Manual.css">
<title>Tips and tricks</title>
</head>
<body >
<a href="Manual004.html"><img src="previous_motif.gif" alt="Previous"></a>
<a href="index.html"><img src="contents_motif.gif" alt="Up"></a>
<a href="Manual006.html"><img src="next_motif.gif" alt="Next"></a>
<hr>
<h1 id="sec36" class="chapter">Chapter 4 Tips and tricks</h1>
<h2 id="sec37" class="section">4.1 Irrefutable patterns</h2>
<p>
<a id="sec:irrefutable"></a>
</p><p>Irrefutable patterns on the RHS (<span style="font-family:monospace">VarParen.lg</span>):
<TABLE BORDER="2" BGCOLOR="#E0E0E0" WIDTH="100%"><TR><TD>
</p><table style="border:0;border-spacing:0" class="cellpadding0"><tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span><span style="font-family:monospace"><span style="font-weight:bold">module</span></span><span style="font-family:monospace"> </span><span style="font-family:monospace"><span style="font-style:italic">VarParen</span></span><span style="font-family:monospace"> </span><span style="font-family:monospace"><span style="font-weight:bold">where</span></span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span><span style="font-family:monospace"><span style="font-weight:bold">import</span></span><span style="font-family:monospace"> </span><span style="font-family:monospace"><span style="font-style:italic">Result</span></span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span><span style="font-family:monospace"><span style="font-weight:bold">newtype</span></span><span style="font-family:monospace"> </span><span style="font-family:monospace"><span style="font-style:italic">Tree</span></span><span style="font-family:monospace"> = </span><span style="font-family:monospace"><span style="font-style:italic">Node</span></span><span style="font-family:monospace"> [</span><span style="font-family:monospace"><span style="font-style:italic">Tree</span></span><span style="font-family:monospace">]</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span><span style="font-family:monospace"><span style="font-weight:bold">deriving</span></span><span style="font-family:monospace"> (</span><span style="font-family:monospace"><span style="font-style:italic">Show</span></span><span style="font-family:monospace">)</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> %{</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span><span style="font-family:monospace"><span style="font-style:italic">Terminal</span></span><span style="font-family:monospace"> = </span><span style="font-family:monospace">’(’</span><span style="font-family:monospace"> | </span><span style="font-family:monospace">’)’</span><span style="font-family:monospace">;</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span><span style="font-family:monospace"><span style="font-style:italic">Nonterminal</span></span><span style="font-family:monospace"> = paren {</span><span style="font-family:monospace"><span style="font-style:italic">Tree</span></span><span style="font-family:monospace">};</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> paren {</span><span style="font-family:monospace"><span style="font-style:italic">Node</span></span><span style="font-family:monospace"> []} : ;</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> {</span><span style="font-family:monospace"><span style="font-style:italic">Node</span></span><span style="font-family:monospace"> (x : xs)} | paren {x}, </span><span style="font-family:monospace">’(’</span><span style="font-family:monospace">, paren {</span><span style="font-family:monospace"><span style="font-style:italic">Node</span></span><span style="font-family:monospace"> xs}, </span><span style="font-family:monospace">’)’</span><span style="font-family:monospace">;</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> }%</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> frown ts = fail "syntax error"</span></td></tr>
</table><p>
</TD></TR></TABLE><P>
</p>
<h2 id="sec38" class="section">4.2 Inherited attributes</h2>
<p>
<a id="sec:inherited"></a>
</p><p>Shows how to simulate inherited attributes: <span style="font-family:monospace">expr</span> has type <span style="font-family:monospace"><span style="font-style:italic">Integer</span></span><span style="font-family:monospace"> -> (</span><span style="font-family:monospace"><span style="font-style:italic">Tree</span></span><span style="font-family:monospace"> </span><span style="font-family:monospace"><span style="font-style:italic">Integer</span></span><span style="font-family:monospace">, </span><span style="font-family:monospace"><span style="font-style:italic">Integer</span></span><span style="font-family:monospace">)</span>, it takes the global minimum to the
rep-min tree (with all elements replaced by the minimum) and the local
minimum (<span style="font-family:monospace">RepMin.lg</span>).
<TABLE BORDER="2" BGCOLOR="#E0E0E0" WIDTH="100%"><TR><TD>
</p><table style="border:0;border-spacing:0" class="cellpadding0"><tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span><span style="font-family:monospace"><span style="font-weight:bold">module</span></span><span style="font-family:monospace"> </span><span style="font-family:monospace"><span style="font-style:italic">RepMin</span></span><span style="font-family:monospace"> </span><span style="font-family:monospace"><span style="font-weight:bold">where</span></span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span><span style="font-family:monospace"><span style="font-weight:bold">data</span></span><span style="font-family:monospace"> </span><span style="font-family:monospace"><span style="font-style:italic">Tree</span></span><span style="font-family:monospace"> a = </span><span style="font-family:monospace"><span style="font-style:italic">Leaf</span></span><span style="font-family:monospace"> a | </span><span style="font-family:monospace"><span style="font-style:italic">Fork</span></span><span style="font-family:monospace"> (</span><span style="font-family:monospace"><span style="font-style:italic">Tree</span></span><span style="font-family:monospace"> a) (</span><span style="font-family:monospace"><span style="font-style:italic">Tree</span></span><span style="font-family:monospace"> a)</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span><span style="font-family:monospace"><span style="font-weight:bold">deriving</span></span><span style="font-family:monospace"> (</span><span style="font-family:monospace"><span style="font-style:italic">Show</span></span><span style="font-family:monospace">)</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span><span style="font-family:monospace"><span style="font-weight:bold">data</span></span><span style="font-family:monospace"> </span><span style="font-family:monospace"><span style="font-style:italic">Terminal</span></span><span style="font-family:monospace"> = </span><span style="font-family:monospace"><span style="font-style:italic">Num</span></span><span style="font-family:monospace"> </span><span style="font-family:monospace"><span style="font-style:italic">Integer</span></span><span style="font-family:monospace"> | </span><span style="font-family:monospace"><span style="font-style:italic">LPar</span></span><span style="font-family:monospace"> | </span><span style="font-family:monospace"><span style="font-style:italic">RPar</span></span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> %{</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span><span style="font-family:monospace"><span style="font-style:italic">Terminal</span></span><span style="font-family:monospace"> = </span><span style="font-family:monospace"><span style="font-style:italic">Num</span></span><span style="font-family:monospace"> {</span><span style="font-family:monospace"><span style="font-style:italic">Integer</span></span><span style="font-family:monospace">}</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> | </span><span style="font-family:monospace"><span style="font-style:italic">LPar</span></span><span style="font-family:monospace"> as "("</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> | </span><span style="font-family:monospace"><span style="font-style:italic">RPar</span></span><span style="font-family:monospace"> as ")";</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span><span style="font-family:monospace"><span style="font-style:italic">Nonterminal</span></span><span style="font-family:monospace"> = * start {</span><span style="font-family:monospace"><span style="font-style:italic">Tree</span></span><span style="font-family:monospace"> </span><span style="font-family:monospace"><span style="font-style:italic">Integer</span></span><span style="font-family:monospace">}</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> | expr {</span><span style="font-family:monospace"><span style="font-style:italic">Integer</span></span><span style="font-family:monospace"> -> (</span><span style="font-family:monospace"><span style="font-style:italic">Tree</span></span><span style="font-family:monospace"> </span><span style="font-family:monospace"><span style="font-style:italic">Integer</span></span><span style="font-family:monospace">, </span><span style="font-family:monospace"><span style="font-style:italic">Integer</span></span><span style="font-family:monospace">)};</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> start { </span><span style="font-family:monospace"><span style="font-weight:bold">let</span></span><span style="font-family:monospace"> (t, m) = f m </span><span style="font-family:monospace"><span style="font-weight:bold">in</span></span><span style="font-family:monospace"> t }</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> : expr {f};</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> expr { \ m -> (</span><span style="font-family:monospace"><span style="font-style:italic">Leaf</span></span><span style="font-family:monospace"> m, i) }</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> : </span><span style="font-family:monospace"><span style="font-style:italic">Num</span></span><span style="font-family:monospace"> {i};</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> expr { \ m -> </span><span style="font-family:monospace"><span style="font-weight:bold">let</span></span><span style="font-family:monospace"> { (tl, ml) = l m</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> ; (tr, mr) = r m }</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span><span style="font-family:monospace"><span style="font-weight:bold">in</span></span><span style="font-family:monospace"> (</span><span style="font-family:monospace"><span style="font-style:italic">Fork</span></span><span style="font-family:monospace"> tl tr, ml ‘min‘ mr) }</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> : expr {l}, "(", expr {r}, ")";</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> }%</span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> </span></td></tr>
<tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> frown ts = fail "syntax error"</span></td></tr>
</table><p>
</TD></TR></TABLE><P>
!avoid layout-sensitive code!</p>
<h2 id="sec39" class="section">4.3 Dealing with conflicts</h2>
<p>
<a id="sec:conflicts"></a>
<TABLE BORDER="2" BGCOLOR="#E0E0E0" WIDTH="100%"><TR><TD>
</p><table style="border:0;border-spacing:0" class="cellpadding0"><tr><td style="text-align:left;white-space:nowrap" ><span style="font-family:monospace">> many’ x : many x;
</span></td></tr>
</table><p>
</TD></TR></TABLE><P>
</p>
<h2 id="sec40" class="section">4.4 Multiple attributes</h2>
<p>
<a id="sec:multattr"></a>
</p>
<hr>
<a href="Manual004.html"><img src="previous_motif.gif" alt="Previous"></a>
<a href="index.html"><img src="contents_motif.gif" alt="Up"></a>
<a href="Manual006.html"><img src="next_motif.gif" alt="Next"></a>
</body>
</html>
|