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#############################################################################
##
#W cache.gd GAP library Chris Jefferson
##
##
#Y Copyright (C) 2017 University of St Andrews, Scotland
##
## This file defines various types of caching data structures
##
#############################################################################
##
#F MemoizePosIntFunction(<function> [,<options> ] )
##
## <#GAPDoc Label="MemoizePosIntFunction">
## <ManSection>
## <Func Name="MemoizePosIntFunction" Arg='function [,options]'/>
##
## <Description>
## <Ref Func="MemoizePosIntFunction"/> returns a function which behaves the same
## as <A>function</A>, except it caches the results; if the new function is
## called with the same input, then any call after the first will return the
## cached value, instead of recomputing it. The cache is flushed by calling
## <Ref Func="FlushCaches"/>.
## <P/>
## The returned function will only accept positive integers.
## <P/>
## This function does not promise to never call <A>function</A> more than
## once for any input -- values may be removed if the cache gets too large,
## or GAP chooses to flush all caches, or if multiple threads try to calculate
## the same value simultaneously.
## <P/>
## The optional second argument is a record which provides a number
## of configuration options. The following options are supported.
## <List>
## <Mark><C>defaults</C> (default an empty list)</Mark>
## <Item>
## Used to initalise the cache, both initially and after each flush.
## </Item>
## <Mark><C>flush</C> (default <K>true</K>)</Mark>
## <Item>
## If this is <K>true</K>, the cache is emptied whenever
## <Ref Func="FlushCaches"/> is called.
## </Item>
## <Mark><C>errorHandler</C> (defaults to <Ref Func="Error"/>)</Mark>
## <Item>
## A function to be called when an input which is not a positive integer
## is passed to the cache. If this function returns a value, that
## value is returned by the cache.
## </Item>
## </List>
## <P/>
## <Example><![CDATA[
## gap> f := MemoizePosIntFunction(
## > function(i) Print("Check: ",i,"\n"); return i*i; end,
## > rec(defaults := [,,50], errorHandler := x -> "Bad") );;
## gap> f(2);
## Check: 2
## 4
## gap> f(2);
## 4
## gap> f(3);
## 50
## gap> f(-3);
## "Bad"
## gap> FlushCaches();
## gap> f(2);
## Check: 2
## 4
## gap> f(3);
## 50
## ]]></Example>
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction("MemoizePosIntFunction");
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