<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Text.Printf</title><link href="ocean.css" rel="stylesheet" type="text/css" title="Ocean" /><script src="haddock-util.js" type="text/javascript"></script><script type="text/javascript">//<![CDATA[ window.onload = function () {pageLoad();setSynopsis("mini_Text-Printf.html");}; //]]> </script></head><body><div id="package-header"><ul class="links" id="page-menu"><li><a href="index.html">Contents</a></li><li><a href="doc-index.html">Index</a></li></ul><p class="caption">base-4.3.1.0: Basic libraries</p></div><div id="content"><div id="module-header"><table class="info"><tr><th>Portability</th><td>portable</td></tr><tr><th>Stability</th><td>provisional</td></tr><tr><th>Maintainer</th><td>lennart@augustsson.net</td></tr></table><p class="caption">Text.Printf</p></div><div id="description"><p class="caption">Description</p><div class="doc"><p>A C printf like formatter. </p></div></div><div id="synopsis"><p id="control.syn" class="caption expander" onclick="toggleSection('syn')">Synopsis</p><ul id="section.syn" class="hide" onclick="toggleSection('syn')"><li class="src short"><a href="#v:printf">printf</a> :: <a href="Text-Printf.html#t:PrintfType">PrintfType</a> r => <a href="Data-Char.html#t:String">String</a> -> r</li><li class="src short"><a href="#v:hPrintf">hPrintf</a> :: <a href="Text-Printf.html#t:HPrintfType">HPrintfType</a> r => <a href="GHC-IO-Handle.html#t:Handle">Handle</a> -> <a href="Data-Char.html#t:String">String</a> -> r</li><li class="src short"><span class="keyword">class</span> <a href="#t:PrintfType">PrintfType</a> t </li><li class="src short"><span class="keyword">class</span> <a href="#t:HPrintfType">HPrintfType</a> t </li><li class="src short"><span class="keyword">class</span> <a href="#t:PrintfArg">PrintfArg</a> a </li><li class="src short"><span class="keyword">class</span> <a href="#t:IsChar">IsChar</a> c </li></ul></div><div id="interface"><h1>Documentation</h1><div class="top"><p class="src"><a name="v:printf" class="def">printf</a> :: <a href="Text-Printf.html#t:PrintfType">PrintfType</a> r => <a href="Data-Char.html#t:String">String</a> -> r</p><div class="doc"><p>Format a variable number of arguments with the C-style formatting string. The return value is either <code><a href="Data-Char.html#t:String">String</a></code> or <code>(<code><a href="System-IO.html#t:IO">IO</a></code> a)</code>. </p><p>The format string consists of ordinary characters and /conversion specifications/, which specify how to format one of the arguments to printf in the output string. A conversion specification begins with the character <code>%</code>, followed by one or more of the following flags: </p><pre> - left adjust (default is right adjust) + always use a sign (+ or -) for signed conversions 0 pad with zeroes rather than spaces </pre><p>followed optionally by a field width: </p><pre> num field width * as num, but taken from argument list </pre><p>followed optionally by a precision: </p><pre> .num precision (number of decimal places) </pre><p>and finally, a format character: </p><pre> c character Char, Int, Integer, ... d decimal Char, Int, Integer, ... o octal Char, Int, Integer, ... x hexadecimal Char, Int, Integer, ... X hexadecimal Char, Int, Integer, ... u unsigned decimal Char, Int, Integer, ... f floating point Float, Double g general format float Float, Double G general format float Float, Double e exponent format float Float, Double E exponent format float Float, Double s string String </pre><p>Mismatch between the argument types and the format string will cause an exception to be thrown at runtime. </p><p>Examples: </p><pre> > printf "%d\n" (23::Int) 23 > printf "%s %s\n" "Hello" "World" Hello World > printf "%.2f\n" pi 3.14 </pre></div></div><div class="top"><p class="src"><a name="v:hPrintf" class="def">hPrintf</a> :: <a href="Text-Printf.html#t:HPrintfType">HPrintfType</a> r => <a href="GHC-IO-Handle.html#t:Handle">Handle</a> -> <a href="Data-Char.html#t:String">String</a> -> r</p><div class="doc"><p>Similar to <code><a href="Text-Printf.html#v:printf">printf</a></code>, except that output is via the specified <code><a href="GHC-IO-Handle.html#t:Handle">Handle</a></code>. The return type is restricted to <code>(<code><a href="System-IO.html#t:IO">IO</a></code> a)</code>. </p></div></div><div class="top"><p class="src"><span class="keyword">class</span> <a name="t:PrintfType" class="def">PrintfType</a> t </p><div class="doc"><p>The <code><a href="Text-Printf.html#t:PrintfType">PrintfType</a></code> class provides the variable argument magic for <code><a href="Text-Printf.html#v:printf">printf</a></code>. Its implementation is intentionally not visible from this module. If you attempt to pass an argument of a type which is not an instance of this class to <code><a href="Text-Printf.html#v:printf">printf</a></code> or <code><a href="Text-Printf.html#v:hPrintf">hPrintf</a></code>, then the compiler will report it as a missing instance of <code><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a></code>. </p></div><div class="subs instances"><p id="control.i:PrintfType" class="caption collapser" onclick="toggleSection('i:PrintfType')">Instances</p><div id="section.i:PrintfType" class="show"><table><tr><td class="src"><a href="Text-Printf.html#t:IsChar">IsChar</a> c => <a href="Text-Printf.html#t:PrintfType">PrintfType</a> [c]</td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:PrintfType">PrintfType</a> (<a href="System-IO.html#t:IO">IO</a> a)</td><td class="doc empty"> </td></tr><tr><td class="src">(<a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> a, <a href="Text-Printf.html#t:PrintfType">PrintfType</a> r) => <a href="Text-Printf.html#t:PrintfType">PrintfType</a> (a -> r)</td><td class="doc empty"> </td></tr></table></div></div></div><div class="top"><p class="src"><span class="keyword">class</span> <a name="t:HPrintfType" class="def">HPrintfType</a> t </p><div class="doc"><p>The <code><a href="Text-Printf.html#t:HPrintfType">HPrintfType</a></code> class provides the variable argument magic for <code><a href="Text-Printf.html#v:hPrintf">hPrintf</a></code>. Its implementation is intentionally not visible from this module. </p></div><div class="subs instances"><p id="control.i:HPrintfType" class="caption collapser" onclick="toggleSection('i:HPrintfType')">Instances</p><div id="section.i:HPrintfType" class="show"><table><tr><td class="src"><a href="Text-Printf.html#t:HPrintfType">HPrintfType</a> (<a href="System-IO.html#t:IO">IO</a> a)</td><td class="doc empty"> </td></tr><tr><td class="src">(<a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> a, <a href="Text-Printf.html#t:HPrintfType">HPrintfType</a> r) => <a href="Text-Printf.html#t:HPrintfType">HPrintfType</a> (a -> r)</td><td class="doc empty"> </td></tr></table></div></div></div><div class="top"><p class="src"><span class="keyword">class</span> <a name="t:PrintfArg" class="def">PrintfArg</a> a </p><div class="subs instances"><p id="control.i:PrintfArg" class="caption collapser" onclick="toggleSection('i:PrintfArg')">Instances</p><div id="section.i:PrintfArg" class="show"><table><tr><td class="src"><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> <a href="Data-Char.html#t:Char">Char</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> <a href="Prelude.html#t:Double">Double</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> <a href="Prelude.html#t:Float">Float</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> <a href="Data-Int.html#t:Int">Int</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> <a href="Data-Int.html#t:Int8">Int8</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> <a href="Data-Int.html#t:Int16">Int16</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> <a href="Data-Int.html#t:Int32">Int32</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> <a href="Data-Int.html#t:Int64">Int64</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> <a href="Prelude.html#t:Integer">Integer</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> <a href="Data-Word.html#t:Word">Word</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> <a href="Data-Word.html#t:Word8">Word8</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> <a href="Data-Word.html#t:Word16">Word16</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> <a href="Data-Word.html#t:Word32">Word32</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> <a href="Data-Word.html#t:Word64">Word64</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="Text-Printf.html#t:IsChar">IsChar</a> c => <a href="Text-Printf.html#t:PrintfArg">PrintfArg</a> [c]</td><td class="doc empty"> </td></tr></table></div></div></div><div class="top"><p class="src"><span class="keyword">class</span> <a name="t:IsChar" class="def">IsChar</a> c </p><div class="subs instances"><p id="control.i:IsChar" class="caption collapser" onclick="toggleSection('i:IsChar')">Instances</p><div id="section.i:IsChar" class="show"><table><tr><td class="src"><a href="Text-Printf.html#t:IsChar">IsChar</a> <a href="Data-Char.html#t:Char">Char</a></td><td class="doc empty"> </td></tr></table></div></div></div></div></div><div id="footer"><p>Produced by <a href="http://www.haskell.org/haddock/">Haddock</a> version 2.9.2</p></div></body></html>