<Section Label="sec-records">
<Heading>Functions for records</Heading>
<ManSection>
<Func Name="AssignGlobals"
Arg="rec" />
<Description>
This function has been transferred from package &RCWA;.
<P/>
It assigns the record components of <A>rec</A>
to global variables with the same names.
<P/>
</Description>
</ManSection>
<Example>
<![CDATA[
gap> r := rec( a := 1, b := 2, c := 3 );;
gap> AssignGlobals( r );
The following global variables have been assigned:
[ "a", "b", "c" ]
gap> [a,b,c];
[ 1, 2, 3 ]
]]>
</Example>
</Section>
<Section Label="sec-options">
<Heading>Option records for functions</Heading>
This functions has been transferred by Chris Jefferson from other packages.
It simplifies the handling of records which are intended
to be used for expressing configuration options.
<A>defaults</A> represents the "default record", and <A>useroptions</A>
lets the user give new values for values in <A>defaults</A>.
<P/>
The function returns a record with the same component names
as <A>defaults</A> and which has the same values as <A>defaults</A>,
except for those component names in <A>useroptions</A>,
where the values in <A>useroptions</A> are used instead.
An error is given if <A>useroptions</A> contains any
component names not in <A>defaults</A>.
If <A>useroptions</A> is an empty list it is treated as an empty record,
and if <A>useroptions</A> is a list of length <M>1</M> containing a record,
this record is used as <A>useroptions</A>.
<P/>
</Description>
</ManSection>
<Example>
<![CDATA[
gap> defaults := rec( a := 1, b := 2, c := 3 );;
gap> OptionRecordWithDefaults( defaults, rec( a := 6) );
rec( a := 6, b := 2, c := 3 )
gap> OptionRecordWithDefaults( defaults, rec( b := 7, c := 8 ) );
rec( a := 1, b := 7, c := 8 )
gap> OptionRecordWithDefaults( defaults, [ ] );
rec( a := 1, b := 2, c := 3 )
gap> OptionRecordWithDefaults( defaults, [ rec( c := 8 ) ] );
rec( a := 1, b := 2, c := 8 )
gap> OptionRecordWithDefaults( defaults, rec( d := 9 ) );
Error, Unknown option: d
gap> OptionRecordWithDefaults( defaults, [ rec( b := 7 ), rec( c := 8 ) ] );
Error, Too many arguments for function
gap> OptionRecordWithDefaults( defaults, [6,7,8] );
Error, Too many arguments for function
]]>
</Example>
This function is designed to support functions with optional arguments
given as a variable record, of the form <C>function(x,y,options...)</C>.
In the following, very contrived, example function, <C>PrintDimensions</C>,
the defaults are given by the variable <C>order</C>
which takes values <C>h</C>, <C>w</C> and <C>d</C>
having default values <M>1</M>, <M>2</M> and <M>3</M>.
If there is a second argument, then
<C>OptionRecordWithDefaults( order, arg[2] );</C> is used to cvhange the values.
These three values then determine the order in which the three dimensions are printed using a <C>SortParallel</C> command.
<Listing>
<![CDATA[
PrintDimensions := function( arg )
local nargs, dim, order, V, L, len, K, i;
nargs := Length( arg );
dim := [ arg[1]!.height, arg[1]!.width, arg[1]!.depth ];
order := rec( h := 1, w := 2, d := 3 );
V := [ "height", "width", "depth" ];
if ( nargs > 1 ) and IsRecord( arg[2] ) then
order := OptionRecordWithDefaults( order, arg[2] );
fi;
L := [ order!.h, order!.w, order!.d ];
len := Length( L );
K := [ 1..len ];
SortParallel( L, K );
Print( "dimensions: " );
Print( V[K[1]], " = ", dim[K[1]], ", " );
Print( V[K[2]], " = ", dim[K[2]], ", " );
Print( V[K[3]], " = ", dim[K[3]], "\n" );
end;;
]]></Listing>
In the example below the first call to <C>PrintDimensions</C>
has just one parameter, <C>mydim</C>, so the default order is used.
In the second call, alternate values for <C>h</C>, <C>w</C> and <C>d</C>
are given, causing the width to be printed first,
and then the depth and height.
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