11.3.8 arg/3   [ISO]

Synopsis

arg(+ArgNum, +Term, -Arg)

unifies Arg with the ArgNumth argument of term Term.

Arguments

ArgNum

integer, must be nonvar and positive

Term

compound, must be nonvar

Arg

term

Description

The arguments are numbered from 1 upwards.

Exceptions

instantiation_error

if ArgNum or Term is unbound.

type_error

if ArgNum is not an integer, or Term is not compound.

domain_error

if ArgNum is an integer less than zero.

Examples

     | ?- arg(2, foo(a,b,c), X).
     
     X = b

See Also

functor/3, =../2, ref-lte-act.