built-in method

`expand_goal/2`

Description

expand_goal(Goal, ExpandedGoal)

Expands a goal. The expansion works as follows: if the first argument is a variable, then it is unified with the second argument; if the first argument is not a variable and there are local or inherited clauses for the goal_expansion/2 hook predicate within scope, then this predicate is recursively called until a fixed-point is reached to provide an expansion that is then unified with the second argument; if the goal_expansion/2 predicate is not within scope, the two arguments are unified.

Automatic goal expansion is only performed at compile time (to expand the body of clauses and meta-directives read from a source file) when using hook objects. This predicate can be used by the user to manually perform goal expansion at runtime (for example, before asserting a clause).

Modes and number of proofs

expand_goal(?term, ?term) - one

Errors

(none)

Examples