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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
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<h1>Penlight</h1>
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<li><a href="../index.html">Index</a></li>
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<h2>Contents</h2>
<ul>
<li><a href="#Functions">Functions</a></li>
</ul>
<h2>Modules</h2>
<ul>
<li><a href="../modules/pl.html">pl</a></li>
<li><a href="../modules/pl.Date.html">pl.Date</a></li>
<li><a href="../modules/pl.List.html">pl.List</a></li>
<li><a href="../modules/pl.Map.html">pl.Map</a></li>
<li><a href="../modules/pl.MultiMap.html">pl.MultiMap</a></li>
<li><a href="../modules/pl.OrderedMap.html">pl.OrderedMap</a></li>
<li><a href="../modules/pl.Set.html">pl.Set</a></li>
<li><a href="../modules/pl.app.html">pl.app</a></li>
<li><a href="../modules/pl.array2d.html">pl.array2d</a></li>
<li><a href="../modules/pl.class.html">pl.class</a></li>
<li><a href="../modules/pl.comprehension.html">pl.comprehension</a></li>
<li><a href="../modules/pl.config.html">pl.config</a></li>
<li><a href="../modules/pl.data.html">pl.data</a></li>
<li><a href="../modules/pl.dir.html">pl.dir</a></li>
<li><a href="../modules/pl.file.html">pl.file</a></li>
<li><strong>pl.func</strong></li>
<li><a href="../modules/pl.input.html">pl.input</a></li>
<li><a href="../modules/pl.lapp.html">pl.lapp</a></li>
<li><a href="../modules/pl.lexer.html">pl.lexer</a></li>
<li><a href="../modules/pl.luabalanced.html">pl.luabalanced</a></li>
<li><a href="../modules/pl.operator.html">pl.operator</a></li>
<li><a href="../modules/pl.path.html">pl.path</a></li>
<li><a href="../modules/pl.permute.html">pl.permute</a></li>
<li><a href="../modules/pl.pretty.html">pl.pretty</a></li>
<li><a href="../modules/pl.seq.html">pl.seq</a></li>
<li><a href="../modules/pl.sip.html">pl.sip</a></li>
<li><a href="../modules/pl.strict.html">pl.strict</a></li>
<li><a href="../modules/pl.stringio.html">pl.stringio</a></li>
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<li><a href="../modules/pl.utils.html">pl.utils</a></li>
<li><a href="../modules/pl.xml.html">pl.xml</a></li>
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<h2>Topics</h2>
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<li><a href="../topics/01-introduction.md.html">01-introduction.md</a></li>
<li><a href="../topics/02-arrays.md.html">02-arrays.md</a></li>
<li><a href="../topics/03-strings.md.html">03-strings.md</a></li>
<li><a href="../topics/04-paths.md.html">04-paths.md</a></li>
<li><a href="../topics/05-dates.md.html">05-dates.md</a></li>
<li><a href="../topics/06-data.md.html">06-data.md</a></li>
<li><a href="../topics/07-functional.md.html">07-functional.md</a></li>
<li><a href="../topics/08-additional.md.html">08-additional.md</a></li>
<li><a href="../topics/09-discussion.md.html">09-discussion.md</a></li>
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<h2>Examples</h2>
<ul>
<li><a href="../examples/seesubst.lua.html">seesubst.lua</a></li>
<li><a href="../examples/sipscan.lua.html">sipscan.lua</a></li>
<li><a href="../examples/symbols.lua.html">symbols.lua</a></li>
<li><a href="../examples/test-cmp.lua.html">test-cmp.lua</a></li>
<li><a href="../examples/test-data.lua.html">test-data.lua</a></li>
<li><a href="../examples/test-listcallbacks.lua.html">test-listcallbacks.lua</a></li>
<li><a href="../examples/test-pretty.lua.html">test-pretty.lua</a></li>
<li><a href="../examples/test-symbols.lua.html">test-symbols.lua</a></li>
<li><a href="../examples/testapp.lua.html">testapp.lua</a></li>
<li><a href="../examples/testclone.lua.html">testclone.lua</a></li>
<li><a href="../examples/testconfig.lua.html">testconfig.lua</a></li>
<li><a href="../examples/testglobal.lua.html">testglobal.lua</a></li>
<li><a href="../examples/testinputfields.lua.html">testinputfields.lua</a></li>
<li><a href="../examples/testinputfields2.lua.html">testinputfields2.lua</a></li>
<li><a href="../examples/testxml.lua.html">testxml.lua</a></li>
<li><a href="../examples/which.lua.html">which.lua</a></li>
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<div id="content">
<h1>Module <code>pl.func</code></h1>
<p>Functional helpers like composition, binding and placeholder expressions.</p>
<p> Placeholder expressions are useful for short anonymous functions, and were
inspired by the Boost Lambda library.</p>
<pre><code>> utils.import 'pl.func'
> ls = List{10,20,30}
> = ls:map(_1+1)
{11,21,31}
</code></pre>
<p> They can also be used to <em>bind</em> particular arguments of a function.</p>
<pre><code>> p = bind(print,'start>',_0)
> p(10,20,30)
> start> 10 20 30
</code></pre>
<p> See <a href="../topics/07-functional.md.html#Creating_Functions_from_Functions">the Guide</a></p>
<p> Dependencies: <a href="../modules/pl.utils.html#">pl.utils</a> , <a href="../modules/pl.tablex.html#">pl.tablex</a> </p>
<h2><a href="#Functions">Functions</a></h2>
<table class="function_list">
<tr>
<td class="name" nowrap><a href="#import">import (tname, context)</a></td>
<td class="summary">wrap a table of functions.</td>
</tr>
<tr>
<td class="name" nowrap><a href="#register">register (fun, name)</a></td>
<td class="summary">register a function for use in placeholder expressions.</td>
</tr>
<tr>
<td class="name" nowrap><a href="#tail">tail (ls)</a></td>
<td class="summary">all elements of a table except the first.</td>
</tr>
<tr>
<td class="name" nowrap><a href="#repr">repr (e, lastpred)</a></td>
<td class="summary">create a string representation of a placeholder expression.</td>
</tr>
<tr>
<td class="name" nowrap><a href="#instantiate">instantiate (e)</a></td>
<td class="summary">instantiate a PE into an actual function.</td>
</tr>
<tr>
<td class="name" nowrap><a href="#I">I (e)</a></td>
<td class="summary">instantiate a PE unless it has already been done.</td>
</tr>
<tr>
<td class="name" nowrap><a href="#curry">curry (fn, p)</a></td>
<td class="summary">bind the first parameter of the function to a value.</td>
</tr>
<tr>
<td class="name" nowrap><a href="#compose">compose (f, g)</a></td>
<td class="summary">create a function which chains two functions.</td>
</tr>
<tr>
<td class="name" nowrap><a href="#bind">bind (fn, ...)</a></td>
<td class="summary">bind the arguments of a function to given values.</td>
</tr>
</table>
<br/>
<br/>
<h2><a name="Functions"></a>Functions</h2>
<dl class="function">
<dt>
<a name = "import"></a>
<strong>import (tname, context)</strong>
</dt>
<dd>
wrap a table of functions. This makes them available for use in
placeholder expressions.
<h3>Parameters:</h3>
<ul>
<li><code><em>tname</em></code>: a table name</li>
<li><code><em>context</em></code>: context to put results, defaults to environment of caller</li>
</ul>
</dd>
<dt>
<a name = "register"></a>
<strong>register (fun, name)</strong>
</dt>
<dd>
register a function for use in placeholder expressions.
<h3>Parameters:</h3>
<ul>
<li><code><em>fun</em></code>: a function</li>
<li><code><em>name</em></code>: an optional name</li>
</ul>
<h3>Returns:</h3>
<ol>
a placeholder functiond
</ol>
</dd>
<dt>
<a name = "tail"></a>
<strong>tail (ls)</strong>
</dt>
<dd>
all elements of a table except the first.
<h3>Parameters:</h3>
<ul>
<li><code><em>ls</em></code>: a list-like table.</li>
</ul>
</dd>
<dt>
<a name = "repr"></a>
<strong>repr (e, lastpred)</strong>
</dt>
<dd>
create a string representation of a placeholder expression.
<h3>Parameters:</h3>
<ul>
<li><code><em>e</em></code>: a placeholder expression</li>
<li><code><em>lastpred</em></code>: not used</li>
</ul>
</dd>
<dt>
<a name = "instantiate"></a>
<strong>instantiate (e)</strong>
</dt>
<dd>
instantiate a PE into an actual function. First we find the largest placeholder used,
e.g. _2; from this a list of the formal parameters can be build. Then we collect and replace
any non-PE values from the PE, and build up a constant binding list.
Finally, the expression can be compiled, and e.__PE_function is set.
<h3>Parameters:</h3>
<ul>
<li><code><em>e</em></code>: a placeholder expression</li>
</ul>
<h3>Returns:</h3>
<ol>
a function
</ol>
</dd>
<dt>
<a name = "I"></a>
<strong>I (e)</strong>
</dt>
<dd>
instantiate a PE unless it has already been done.
<h3>Parameters:</h3>
<ul>
<li><code><em>e</em></code>: a placeholder expression</li>
</ul>
<h3>Returns:</h3>
<ol>
the function
</ol>
</dd>
<dt>
<a name = "curry"></a>
<strong>curry (fn, p)</strong>
</dt>
<dd>
bind the first parameter of the function to a value.
<h3>Parameters:</h3>
<ul>
<li><code><em>fn</em></code>: a function of one or more arguments</li>
<li><code><em>p</em></code>: a value</li>
</ul>
<h3>Usage:</h3>
<ul>
<pre class="example">(curry(math.max,10))(20) == math.max(10,20)</pre>
</ul>
<h3>Returns:</h3>
<ol>
a function of one less argument
</ol>
</dd>
<dt>
<a name = "compose"></a>
<strong>compose (f, g)</strong>
</dt>
<dd>
create a function which chains two functions.
<h3>Parameters:</h3>
<ul>
<li><code><em>f</em></code>: a function of at least one argument</li>
<li><code><em>g</em></code>: a function of at least one argument</li>
</ul>
<h3>Usage:</h3>
<ul>
<pre class="example">printf = compose(io.write,string.format)</pre>
</ul>
<h3>Returns:</h3>
<ol>
a function
</ol>
</dd>
<dt>
<a name = "bind"></a>
<strong>bind (fn, ...)</strong>
</dt>
<dd>
bind the arguments of a function to given values.
bind(fn,v,_2) is equivalent to curry(fn,v).
<h3>Parameters:</h3>
<ul>
<li><code><em>fn</em></code>: a function of at least one argument</li>
<li><code><em>...</em></code>: values or placeholder variables</li>
</ul>
<h3>Usage:</h3>
<ul>
<li><pre class="example">(bind(f,_1,a))(b) == f(a,b)</pre></li>
<li><pre class="example">(bind(f,_2,_1))(a,b) == f(b,a)</pre></li>
</ul>
<h3>Returns:</h3>
<ol>
a function
</ol>
</dd>
</dl>
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