<!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 >Control.Arrow.ArrowState</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_Control-Arrow-ArrowState.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" >hxt-8.3.2: A collection of tools for processing XML with Haskell.</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" >Control.Arrow.ArrowState</FONT ></TD ><TD ALIGN="right" ><TABLE CLASS="narrow" CELLSPACING="0" CELLPADDING="0" ><TR ><TD CLASS="infohead" >Portability</TD ><TD CLASS="infoval" >multy parameter classes and functional depenedencies required</TD ></TR ><TR ><TD CLASS="infohead" >Stability</TD ><TD CLASS="infoval" >experimental</TD ></TR ><TR ><TD CLASS="infohead" >Maintainer</TD ><TD CLASS="infoval" >Uwe Schmidt (uwe\@fh-wedel.de)</TD ></TR ></TABLE ></TD ></TR ></TABLE ></TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="section1" >Description</TD ></TR ><TR ><TD CLASS="doc" ><P >Arrows for managing an explicit state </P ><P >State arrows work similar to state monads. A state value is threaded through the application of arrows. </P ></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" ><SPAN CLASS="keyword" >class</SPAN > <A HREF="/usr/share/doc/ghc/libraries/base/Control-Arrow.html#t%3AArrow" >Arrow</A > a => <A HREF="#t%3AArrowState" >ArrowState</A > s a | a -> s <SPAN CLASS="keyword" >where</SPAN ></TD ></TR ><TR ><TD CLASS="body" ><TABLE CLASS="vanilla" CELLSPACING="0" CELLPADDING="0" ><TR ><TD CLASS="decl" ><A HREF="#v%3AchangeState" >changeState</A > :: (s -> b -> s) -> a b b</TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3AaccessState" >accessState</A > :: (s -> b -> c) -> a b c</TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3AgetState" >getState</A > :: a b s</TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3AsetState" >setState</A > :: a s s</TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3AnextState" >nextState</A > :: (s -> s) -> a b s</TD ></TR ></TABLE ></TD ></TR ></TABLE ></TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="section1" >Documentation</TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><SPAN CLASS="keyword" >class</SPAN > <A HREF="/usr/share/doc/ghc/libraries/base/Control-Arrow.html#t%3AArrow" >Arrow</A > a => <A NAME="t:ArrowState" ><A NAME="t%3AArrowState" ></A ></A ><B >ArrowState</B > s a | a -> s <SPAN CLASS="keyword" >where</SPAN ></TD ></TR ><TR ><TD CLASS="body" ><TABLE CLASS="vanilla" CELLSPACING="0" CELLPADDING="0" ><TR ><TD CLASS="ndoc" ><P >The interface for accessing and changing the state component. </P ><P >Multi parameter classes and functional dependencies are required. </P ></TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="section4" >Methods</TD ></TR ><TR ><TD CLASS="body" ><TABLE CLASS="vanilla" CELLSPACING="0" CELLPADDING="0" ><TR ><TD CLASS="decl" ><A NAME="v:changeState" ><A NAME="v%3AchangeState" ></A ></A ><B >changeState</B > :: (s -> b -> s) -> a b b</TD ></TR ><TR ><TD CLASS="doc" >change the state of a state arrow by applying a function for computing a new state from the old and the arrow input. Result is the arrow input </TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:accessState" ><A NAME="v%3AaccessState" ></A ></A ><B >accessState</B > :: (s -> b -> c) -> a b c</TD ></TR ><TR ><TD CLASS="doc" >access the state with a function using the arrow input as data for selecting state components. </TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:getState" ><A NAME="v%3AgetState" ></A ></A ><B >getState</B > :: a b s</TD ></TR ><TR ><TD CLASS="doc" ><P >read the complete state, ignore arrow input </P ><P >definition: <TT > getState = accessState (\ s x -> s) </TT > </P ></TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:setState" ><A NAME="v%3AsetState" ></A ></A ><B >setState</B > :: a s s</TD ></TR ><TR ><TD CLASS="doc" ><P >overwrite the old state </P ><P >definition: <TT > setState = changeState (\ s x -> x) </TT > </P ></TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:nextState" ><A NAME="v%3AnextState" ></A ></A ><B >nextState</B > :: (s -> s) -> a b s</TD ></TR ><TR ><TD CLASS="doc" ><P >change state (and ignore input) and return new state </P ><P >convenience function, usefull for generating e.g. unique identifiers: </P ><P >example with SLA state list arrows </P ><PRE > newId :: SLA Int b String newId = nextState (+1) >>> arr (('#':) . show) runSLA 0 (newId <+> newId <+> newId) undefined = ["#1", "#2", "#3"] </PRE ></TD ></TR ></TABLE ></TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="section4" ><IMG SRC="minus.gif" CLASS="coll" ONCLICK="toggle(this,'i:ArrowState')" ALT="show/hide" > Instances</TD ></TR ><TR ><TD CLASS="body" ><DIV ID="i:ArrowState" STYLE="display:block;" ><TABLE CLASS="vanilla" CELLSPACING="1" CELLPADDING="0" ><TR ><TD CLASS="decl" ><A HREF="Control-Arrow-ArrowState.html#t%3AArrowState" >ArrowState</A > s (<A HREF="Control-Arrow-StateListArrow.html#t%3ASLA" >SLA</A > s)</TD ></TR ><TR ><TD CLASS="decl" ><A HREF="Control-Arrow-ArrowState.html#t%3AArrowState" >ArrowState</A > s (<A HREF="Control-Arrow-IOStateListArrow.html#t%3AIOSLA" >IOSLA</A > s)</TD ></TR ></TABLE ></DIV ></TD ></TR ></TABLE ></TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="botbar" >Produced by <A HREF="http://www.haskell.org/haddock/" >Haddock</A > version 2.5.0</TD ></TR ></TABLE ></BODY ></HTML >