<!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.Concurrent.SampleVar</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-Concurrent-SampleVar.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" >Control.Concurrent.SampleVar</FONT ></TD ><TD ALIGN="right" ><TABLE CLASS="narrow" CELLSPACING="0" CELLPADDING="0" ><TR ><TD CLASS="infohead" >Portability</TD ><TD CLASS="infoval" >non-portable (concurrency)</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" >Sample Variables </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" >Sample variables </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" >type</SPAN > <A HREF="#t%3ASampleVar" >SampleVar</A > a = <A HREF="Control-Concurrent-MVar.html#t%3AMVar" >MVar</A > (<A HREF="../ghc-prim/GHC-Types.html#t%3AInt" >Int</A >, <A HREF="Control-Concurrent-MVar.html#t%3AMVar" >MVar</A > a)</TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3AnewEmptySampleVar" >newEmptySampleVar</A > :: <A HREF="System-IO.html#t%3AIO" >IO</A > (<A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A > a)</TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3AnewSampleVar" >newSampleVar</A > :: a -> <A HREF="System-IO.html#t%3AIO" >IO</A > (<A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A > a)</TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3AemptySampleVar" >emptySampleVar</A > :: <A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A > a -> <A HREF="System-IO.html#t%3AIO" >IO</A > <A HREF="../ghc-prim/GHC-Unit.html#t%3A%28%29" >()</A ></TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3AreadSampleVar" >readSampleVar</A > :: <A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A > a -> <A HREF="System-IO.html#t%3AIO" >IO</A > a</TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3AwriteSampleVar" >writeSampleVar</A > :: <A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A > a -> a -> <A HREF="System-IO.html#t%3AIO" >IO</A > <A HREF="../ghc-prim/GHC-Unit.html#t%3A%28%29" >()</A ></TD ></TR ><TR ><TD CLASS="s8" ></TD ></TR ><TR ><TD CLASS="decl" ><A HREF="#v%3AisEmptySampleVar" >isEmptySampleVar</A > :: <A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A > a -> <A HREF="System-IO.html#t%3AIO" >IO</A > <A HREF="../ghc-prim/GHC-Bool.html#t%3ABool" >Bool</A ></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" >Sample Variables </A ></A ></TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><SPAN CLASS="keyword" >type</SPAN > <A NAME="t:SampleVar" ><A NAME="t%3ASampleVar" ></A ></A ><B >SampleVar</B > a = <A HREF="Control-Concurrent-MVar.html#t%3AMVar" >MVar</A > (<A HREF="../ghc-prim/GHC-Types.html#t%3AInt" >Int</A >, <A HREF="Control-Concurrent-MVar.html#t%3AMVar" >MVar</A > a)</TD ></TR ><TR ><TD CLASS="doc" ><P >Sample variables are slightly different from a normal <TT ><A HREF="Control-Concurrent-MVar.html#t%3AMVar" >MVar</A ></TT >: </P ><UL ><LI > Reading an empty <TT ><A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A ></TT > causes the reader to block. (same as <TT ><A HREF="Control-Concurrent-MVar.html#v%3AtakeMVar" >takeMVar</A ></TT > on empty <TT ><A HREF="Control-Concurrent-MVar.html#t%3AMVar" >MVar</A ></TT >) </LI ><LI > Reading a filled <TT ><A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A ></TT > empties it and returns value. (same as <TT ><A HREF="Control-Concurrent-MVar.html#v%3AtakeMVar" >takeMVar</A ></TT >) </LI ><LI > Writing to an empty <TT ><A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A ></TT > fills it with a value, and potentially, wakes up a blocked reader (same as for <TT ><A HREF="Control-Concurrent-MVar.html#v%3AputMVar" >putMVar</A ></TT > on empty <TT ><A HREF="Control-Concurrent-MVar.html#t%3AMVar" >MVar</A ></TT >). </LI ><LI > Writing to a filled <TT ><A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A ></TT > overwrites the current value. (different from <TT ><A HREF="Control-Concurrent-MVar.html#v%3AputMVar" >putMVar</A ></TT > on full <TT ><A HREF="Control-Concurrent-MVar.html#t%3AMVar" >MVar</A ></TT >.) </LI ></UL ></TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:newEmptySampleVar" ><A NAME="v%3AnewEmptySampleVar" ></A ></A ><B >newEmptySampleVar</B > :: <A HREF="System-IO.html#t%3AIO" >IO</A > (<A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A > a)</TD ></TR ><TR ><TD CLASS="doc" >Build a new, empty, <TT ><A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A ></TT > </TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:newSampleVar" ><A NAME="v%3AnewSampleVar" ></A ></A ><B >newSampleVar</B > :: a -> <A HREF="System-IO.html#t%3AIO" >IO</A > (<A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A > a)</TD ></TR ><TR ><TD CLASS="doc" >Build a <TT ><A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A ></TT > with an initial value. </TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:emptySampleVar" ><A NAME="v%3AemptySampleVar" ></A ></A ><B >emptySampleVar</B > :: <A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A > a -> <A HREF="System-IO.html#t%3AIO" >IO</A > <A HREF="../ghc-prim/GHC-Unit.html#t%3A%28%29" >()</A ></TD ></TR ><TR ><TD CLASS="doc" >If the SampleVar is full, leave it empty. Otherwise, do nothing. </TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:readSampleVar" ><A NAME="v%3AreadSampleVar" ></A ></A ><B >readSampleVar</B > :: <A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A > a -> <A HREF="System-IO.html#t%3AIO" >IO</A > a</TD ></TR ><TR ><TD CLASS="doc" >Wait for a value to become available, then take it and return. </TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:writeSampleVar" ><A NAME="v%3AwriteSampleVar" ></A ></A ><B >writeSampleVar</B > :: <A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A > a -> a -> <A HREF="System-IO.html#t%3AIO" >IO</A > <A HREF="../ghc-prim/GHC-Unit.html#t%3A%28%29" >()</A ></TD ></TR ><TR ><TD CLASS="doc" >Write a value into the <TT ><A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A ></TT >, overwriting any previous value that was there. </TD ></TR ><TR ><TD CLASS="s15" ></TD ></TR ><TR ><TD CLASS="decl" ><A NAME="v:isEmptySampleVar" ><A NAME="v%3AisEmptySampleVar" ></A ></A ><B >isEmptySampleVar</B > :: <A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A > a -> <A HREF="System-IO.html#t%3AIO" >IO</A > <A HREF="../ghc-prim/GHC-Bool.html#t%3ABool" >Bool</A ></TD ></TR ><TR ><TD CLASS="doc" ><P >Returns <TT ><A HREF="../ghc-prim/GHC-Bool.html#v%3ATrue" >True</A ></TT > if the <TT ><A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A ></TT > is currently empty. </P ><P >Note that this function is only useful if you know that no other threads can be modifying the state of the <TT ><A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A ></TT >, because otherwise the state of the <TT ><A HREF="Control-Concurrent-SampleVar.html#t%3ASampleVar" >SampleVar</A ></TT > may have changed by the time you see the result of <TT ><A HREF="Control-Concurrent-SampleVar.html#v%3AisEmptySampleVar" >isEmptySampleVar</A ></TT >. </P ></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 >