arg/3
Module: builtins
arg/3 — access the arguments of a structured term
FORMS
arg(Nth, Structure, Argument)
DESCRIPTION
Argument will be unified with the Nth argument of Structure. Nth must be a positive integer. Structure should be a compound term whose arity is greater than or equal to Nth. When these conditions hold, Argument will be unified with the Nth argument of Structure.
EXAMPLES
?- arg(2,stooges(larry,moe,curly),X).
X=moe
yes.
?- arg(2,[a,b,c],X).
X=[b,c]
yes.
ERRORS
If Nth is not an integer greater than 0 and less than or equal to the arity of Structure, arg/3 will fail. Structure must be instantiated to a structured term.