1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<!-- Copyright (C) 1988-2021 Free Software Foundation, Inc. 4 5Permission is granted to copy, distribute and/or modify this document 6under the terms of the GNU Free Documentation License, Version 1.3 or 7any later version published by the Free Software Foundation; with the 8Invariant Sections being "Free Software" and "Free Software Needs 9Free Documentation", with the Front-Cover Texts being "A GNU Manual," 10and with the Back-Cover Texts as in (a) below. 11 12(a) The FSF's Back-Cover Text is: "You are free to copy and modify 13this GNU Manual. 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If the value is handled by this pretty-printer, then 88<var>lookup-function</var> returns an object of type 89<gdb:pretty-printer-worker> to perform the actual pretty-printing. 90Otherwise <var>lookup-function</var> returns <code>#f</code>. 91</p></dd></dl> 92 93<dl> 94<dt><a name="index-pretty_002dprinter_003f"></a>Scheme Procedure: <strong>pretty-printer?</strong> <em>object</em></dt> 95<dd><p>Return <code>#t</code> if <var>object</var> is a <code><gdb:pretty-printer></code> object. 96Otherwise return <code>#f</code>. 97</p></dd></dl> 98 99<dl> 100<dt><a name="index-pretty_002dprinter_002denabled_003f"></a>Scheme Procedure: <strong>pretty-printer-enabled?</strong> <em>pretty-printer</em></dt> 101<dd><p>Return <code>#t</code> if <var>pretty-printer</var> is enabled. 102Otherwise return <code>#f</code>. 103</p></dd></dl> 104 105<dl> 106<dt><a name="index-set_002dpretty_002dprinter_002denabled_0021"></a>Scheme Procedure: <strong>set-pretty-printer-enabled!</strong> <em>pretty-printer flag</em></dt> 107<dd><p>Set the enabled flag of <var>pretty-printer</var> to <var>flag</var>. 108The value returned is unspecified. 109</p></dd></dl> 110 111<dl> 112<dt><a name="index-pretty_002dprinters"></a>Scheme Procedure: <strong>pretty-printers</strong></dt> 113<dd><p>Return the list of global pretty-printers. 114</p></dd></dl> 115 116<dl> 117<dt><a name="index-set_002dpretty_002dprinters_0021"></a>Scheme Procedure: <strong>set-pretty-printers!</strong> <em>pretty-printers</em></dt> 118<dd><p>Set the list of global pretty-printers to <var>pretty-printers</var>. 119The value returned is unspecified. 120</p></dd></dl> 121 122<dl> 123<dt><a name="index-make_002dpretty_002dprinter_002dworker"></a>Scheme Procedure: <strong>make-pretty-printer-worker</strong> <em>display-hint to-string children</em></dt> 124<dd><p>Return an object of type <code><gdb:pretty-printer-worker></code>. 125</p> 126<p>This function takes three parameters: 127</p> 128<dl compact="compact"> 129<dt>‘<samp>display-hint</samp>’</dt> 130<dd><p><var>display-hint</var> provides a hint to <small>GDB</small> or <small>GDB</small> 131front end via MI to change the formatting of the value being printed. 132The value must be a string or <code>#f</code> (meaning there is no hint). 133Several values for <var>display-hint</var> 134are predefined by <small>GDB</small>: 135</p> 136<dl compact="compact"> 137<dt>‘<samp>array</samp>’</dt> 138<dd><p>Indicate that the object being printed is “array-like”. The CLI 139uses this to respect parameters such as <code>set print elements</code> and 140<code>set print array</code>. 141</p> 142</dd> 143<dt>‘<samp>map</samp>’</dt> 144<dd><p>Indicate that the object being printed is “map-like”, and that the 145children of this value can be assumed to alternate between keys and 146values. 147</p> 148</dd> 149<dt>‘<samp>string</samp>’</dt> 150<dd><p>Indicate that the object being printed is “string-like”. If the 151printer’s <code>to-string</code> function returns a Guile string of some 152kind, then <small>GDB</small> will call its internal language-specific 153string-printing function to format the string. For the CLI this means 154adding quotation marks, possibly escaping some characters, respecting 155<code>set print elements</code>, and the like. 156</p></dd> 157</dl> 158 159</dd> 160<dt>‘<samp>to-string</samp>’</dt> 161<dd><p><var>to-string</var> is either a function of one parameter, the 162<code><gdb:pretty-printer-worker></code> object, or <code>#f</code>. 163</p> 164<p>When printing from the CLI, if the <code>to-string</code> method exists, 165then <small>GDB</small> will prepend its result to the values returned by 166<code>children</code>. Exactly how this formatting is done is dependent on 167the display hint, and may change as more hints are added. Also, 168depending on the print settings (see <a href="Print-Settings.html#Print-Settings">Print Settings</a>), the CLI may 169print just the result of <code>to-string</code> in a stack trace, omitting 170the result of <code>children</code>. 171</p> 172<p>If this method returns a string, it is printed verbatim. 173</p> 174<p>Otherwise, if this method returns an instance of <code><gdb:value></code>, 175then <small>GDB</small> prints this value. This may result in a call to 176another pretty-printer. 177</p> 178<p>If instead the method returns a Guile value which is convertible to a 179<code><gdb:value></code>, then <small>GDB</small> performs the conversion and prints 180the resulting value. Again, this may result in a call to another 181pretty-printer. Guile scalars (integers, floats, and booleans) and 182strings are convertible to <code><gdb:value></code>; other types are not. 183</p> 184<p>Finally, if this method returns <code>#f</code> then no further operations 185are peformed in this method and nothing is printed. 186</p> 187<p>If the result is not one of these types, an exception is raised. 188</p> 189<p><var>to-string</var> may also be <code>#f</code> in which case it is left to 190<var>children</var> to print the value. 191</p> 192</dd> 193<dt>‘<samp>children</samp>’</dt> 194<dd><p><var>children</var> is either a function of one parameter, the 195<code><gdb:pretty-printer-worker></code> object, or <code>#f</code>. 196</p> 197<p><small>GDB</small> will call this function on a pretty-printer to compute the 198children of the pretty-printer’s value. 199</p> 200<p>This function must return a <gdb:iterator> object. 201Each item returned by the iterator must be a tuple holding 202two elements. The first element is the “name” of the child; the 203second element is the child’s value. The value can be any Guile 204object which is convertible to a <small>GDB</small> value. 205</p> 206<p>If <var>children</var> is <code>#f</code>, <small>GDB</small> will act 207as though the value has no children. 208</p> 209<p>Children may be hidden from display based on the value of ‘<samp>set 210print max-depth</samp>’ (see <a href="Print-Settings.html#Print-Settings">Print Settings</a>). 211</p></dd> 212</dl> 213</dd></dl> 214 215<p><small>GDB</small> provides a function which can be used to look up the 216default pretty-printer for a <code><gdb:value></code>: 217</p> 218<dl> 219<dt><a name="index-default_002dvisualizer"></a>Scheme Procedure: <strong>default-visualizer</strong> <em>value</em></dt> 220<dd><p>This function takes a <code><gdb:value></code> object as an argument. If a 221pretty-printer for this value exists, then it is returned. If no such 222printer exists, then this returns <code>#f</code>. 223</p></dd></dl> 224 225<hr> 226<div class="header"> 227<p> 228Next: <a href="Selecting-Guile-Pretty_002dPrinters.html#Selecting-Guile-Pretty_002dPrinters" accesskey="n" rel="next">Selecting Guile Pretty-Printers</a>, Previous: <a href="Types-In-Guile.html#Types-In-Guile" accesskey="p" rel="previous">Types In Guile</a>, Up: <a href="Guile-API.html#Guile-API" accesskey="u" rel="up">Guile API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> 229</div> 230 231 232 233</body> 234</html> 235