<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <!--Rendered using the Haskell Html Library v0.2--> <HTML ><HEAD ><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=UTF-8" ><TITLE >Data.Function</TITLE ><LINK HREF="haddock.css" REL="stylesheet" TYPE="text/css" ><SCRIPT SRC="haddock-util.js" TYPE="text/javascript" ></SCRIPT ><SCRIPT TYPE="text/javascript" >window.onload = function () {setSynopsis("mini_Data-Function.html")};</SCRIPT ></HEAD ><BODY ><TABLE CLASS="vanilla" CELLSPACING="0" CELLPADDING="0" ><TR ><TD CLASS="topbar" ><TABLE CLASS="vanilla" CELLSPACING="0" CELLPADDING="0" ><TR ><TD ><IMG SRC="haskell_icon.gif" WIDTH="16" HEIGHT="16" ALT=" " ></TD ><TD CLASS="title" >base-4.1.0.0: Basic libraries</TD ><TD CLASS="topbut" ><A HREF="index.html" >Contents</A ></TD ><TD CLASS="topbut" ><A HREF="doc-index.html" >Index</A ></TD ></TR ></TABLE ></TD ></TR ><TR ><TD CLASS="modulebar" ><TABLE CLASS="vanilla" CELLSPACING="0" CELLPADDING="0" ><TR ><TD ><FONT SIZE="6" >Data.Function</FONT ></TD ><TD ALIGN="right" ><TABLE CLASS="narrow" CELLSPACING="0" CELLPADDING="0" ><TR ><TD CLASS="infohead" >Portability</TD ><TD CLASS="infoval" >portable</TD ></TR ><TR ><TD CLASS="infohead" >Stability</TD ><TD CLASS="infoval" >experimental</TD ></TR ><TR ><TD CLASS="infohead" >Maintainer</TD ><TD CLASS="infoval" >libraries@haskell.org</TD ></TR ></TABLE ></TD ></TR ></TABLE ></TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD ><TABLE CLASS="vanilla" CELLSPACING="0" CELLPADDING="0" ><TR ><TD CLASS="section4" ><B >Contents</B ></TD ></TR ><TR ><TD ><DL ><DT ><A HREF="#1" ><A HREF="Prelude.html" >Prelude</A > re-exports </A ></DT ><DT ><A HREF="#2" >Other combinators </A ></DT ></DL ></TD ></TR ></TABLE ></TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="section1" >Description</TD ></TR ><TR ><TD CLASS="doc" >Simple combinators working solely on and with functions. </TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="section1" >Synopsis</TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="body" ><TABLE CLASS="vanilla" CELLSPACING="0" CELLPADDING="0" ><TR ><TD CLASS="decl" ><A HREF="#v%3Aid" >id</A > :: a -> a</TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3Aconst" >const</A > :: a -> b -> a</TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3A." >(.)</A > :: (b -> c) -> (a -> b) -> a -> c</TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3Aflip" >flip</A > :: (a -> b -> c) -> b -> a -> c</TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3A%24" >($)</A > :: (a -> b) -> a -> b</TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3Afix" >fix</A > :: (a -> a) -> a</TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3Aon" >on</A > :: (b -> b -> c) -> (a -> b) -> a -> a -> c</TD ></TR ></TABLE ></TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="section1" ><A NAME="1" ><A NAME="1" ><A HREF="Prelude.html" >Prelude</A > re-exports </A ></A ></TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:id" ><A NAME="v%3Aid" ></A ></A ><B >id</B > :: a -> a</TD ></TR ><TR ><TD CLASS="doc" >Identity function. </TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:const" ><A NAME="v%3Aconst" ></A ></A ><B >const</B > :: a -> b -> a</TD ></TR ><TR ><TD CLASS="doc" >Constant function. </TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:." ><A NAME="v%3A." ></A ></A ><B >(.)</B > :: (b -> c) -> (a -> b) -> a -> c</TD ></TR ><TR ><TD CLASS="doc" >Function composition. </TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:flip" ><A NAME="v%3Aflip" ></A ></A ><B >flip</B > :: (a -> b -> c) -> b -> a -> c</TD ></TR ><TR ><TD CLASS="doc" ><TT ><TT ><A HREF="Data-Function.html#v%3Aflip" >flip</A ></TT > f</TT > takes its (first) two arguments in the reverse order of <TT >f</TT >. </TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:$" ><A NAME="v%3A%24" ></A ></A ><B >($)</B > :: (a -> b) -> a -> b</TD ></TR ><TR ><TD CLASS="doc" ><P >Application operator. This operator is redundant, since ordinary application <TT >(f x)</TT > means the same as <TT >(f <TT ><A HREF="Data-Function.html#v%3A%24" >$</A ></TT > x)</TT >. However, <TT ><A HREF="Data-Function.html#v%3A%24" >$</A ></TT > has low, right-associative binding precedence, so it sometimes allows parentheses to be omitted; for example: </P ><PRE > f $ g $ h x = f (g (h x)) </PRE ><P >It is also useful in higher-order situations, such as <TT ><TT ><A HREF="Data-List.html#v%3Amap" >map</A ></TT > (<TT ><A HREF="Data-Function.html#v%3A%24" >$</A ></TT > 0) xs</TT >, or <TT >Data.List.zipWith (<TT ><A HREF="Data-Function.html#v%3A%24" >$</A ></TT >) fs xs</TT >. </P ></TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="section1" ><A NAME="2" ><A NAME="2" >Other combinators </A ></A ></TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:fix" ><A NAME="v%3Afix" ></A ></A ><B >fix</B > :: (a -> a) -> a</TD ></TR ><TR ><TD CLASS="doc" ><TT ><TT ><A HREF="Data-Function.html#v%3Afix" >fix</A ></TT > f</TT > is the least fixed point of the function <TT >f</TT >, i.e. the least defined <TT >x</TT > such that <TT >f x = x</TT >. </TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:on" ><A NAME="v%3Aon" ></A ></A ><B >on</B > :: (b -> b -> c) -> (a -> b) -> a -> a -> c</TD ></TR ><TR ><TD CLASS="doc" ><P ><TT >(*) `on` f = \x y -> f x * f y</TT >. </P ><P >Typical usage: <TT >Data.List.sortBy (<TT ><A HREF="Data-Ord.html#v%3Acompare" >compare</A ></TT > `on` <TT ><A HREF="Data-Tuple.html#v%3Afst" >fst</A ></TT >)</TT >. </P ><P >Algebraic properties: </P ><UL ><LI > <TT >(*) `on` <TT ><A HREF="Data-Function.html#v%3Aid" >id</A ></TT > = (*)</TT > (if <TT >(*) ∉ {⊥, <TT ><A HREF="Data-Function.html#v%3Aconst" >const</A ></TT > ⊥}</TT >) </LI ><LI ><PRE >((*) `on` f) `on` g = (*) `on` (f . g)</PRE ></LI ><LI ><PRE ><TT ><A HREF="Data-Function.html#v%3Aflip" >flip</A ></TT > on f . <TT ><A HREF="Data-Function.html#v%3Aflip" >flip</A ></TT > on g = <TT ><A HREF="Data-Function.html#v%3Aflip" >flip</A ></TT > on (g . f)</PRE ></LI ></UL ></TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="botbar" >Produced by <A HREF="http://www.haskell.org/haddock/" >Haddock</A > version 2.4.2</TD ></TR ></TABLE ></BODY ></HTML >