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Functional Values

Functions, like types, are first class values in Fabl. An expression of the form

<function-name>[<Type1>,<Type2> ... <Typen>]

returns the function, if any, with name <function-name> and input types <Type₁> ... <Type_n> For example:

int function twice(int n){return n+n}
var fnv = twice[int];
fnv(4);
-->8

SeqOf(int) function mapOver(SeqOf(int) vls,Function(int,int) fn)
{
var SeqOf(int) rs,int ln,i;
ln = length(vls);
rs = new(SeqOf(int));
for (i=0;i<ln;i++) push(rs,fn(vls[i]));
return rs;
}

mapOver([1,2,3],fnv);
-->[2,4,6]

supplyArgument

The function

<SupFunType> supplyArgument(<FunType> fn,<Type0> val)

returns the function sfn that results from supplying val as the fixed value of the first argument to fn; sfn takes one fewer argument than fn. Here is an example:

install(namespace('geom'));
install(namespace('geom2d'));
install(namespace('libgeom2d'));
push(path,namespace('libgeom2d'));


var p0 = mkPoint(1,2);

var distanceFromP0 = supplyArgument(distance[geom2d:Point,geom2d:Point],p0);

distanceFromP0(mkPoint(3,2));
-->2

As of version 2.0.11, the supplyArgument primitive cannot be iterated. So, for example:

supplyArgument(distanceFromP0,mkPoint(4,5));

yields the message;

-->Not yet: iterated supplyArgument