<!-- This is an automatically generated file. -->
<Chapter Label="Chapter_Memoisation">
<Heading>Memoisation</Heading>
<P/>
<Package>datastructures</Package> provides simple ways to cache return values of pure functions.
<P/>
<Section Label="Chapter_Memoisation_Section_Memoisation_with_HashMap">
<Heading>Memoisation with HashMap</Heading>
<P/>
<ManSection>
<Func Arg="function [, options]" Name="MemoizeFunction" />
<Returns>A function
</Returns>
<Description>
<C>MemoizeFunction</C> returns a function which behaves the same as <A>function</A>,
except that it caches the return value of <A>function</A>.
The cache can be flushed by calling <Ref Func="FlushCaches" BookName="ref"/>.
<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>flush</C> (default <K>true</K>)</Mark>
<Item>
If this is <K>true</K>, the cache is emptied whenever
<Ref Func="FlushCaches" BookName="ref"/> is called.
</Item>
<Mark><C>contract</C> (defaults to <Ref Func="ReturnTrue" BookName="ref"/>)</Mark>
<Item>
A function that is called on the arguments given to <A>function</A>.
If this function returns <K>false</K>, then <C>errorHandler</C> is
called.
</Item>
<Mark><C>errorHandler</C> (defaults to none)</Mark>
<Item>
A function to be called when an input that does not fulfil
<C>contract</C> is passed to the cache.
</Item>
</List>
<P/>
</Description>
</ManSection>
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