function_expansion/3

user:function_expansion(+Term, -Replacement, -Guard) is semidet

Like term_expansion/2, function_expansion/3 provides for macro expansion of Prolog source code. In this case, by expanding Term which is nested inside a parent term. Term is replaced with Replacement. Guard is placed as a conjunction before the parent term. Guard typically binds Replacement in some useful fashion.

For example, a function macro which doubles its argument might expand this

user:function_expansion(double(X), Y, Y is 2*X).
main :-
    V = 9,
    format('~p times 2 is ~p~n', [V, double(V)]).

into this

==
main :-
    V = 9,
    A is 2*V,
    format('~p times 2 is ~p~n', [V, A]).
==

Mathematical constants might be implemented like

==
user:function_expansion(pi, 3.14159, true).
==