->/2

Synopsis

+-P -> +*Q

"Local cut"

If P then Q else fail, using first solution of P only.

Arguments

P callable [MOD]

Q callable [MOD]

Description

When occurring other than as the first argument of a disjunction operator (| or ;), this is equivalent to:

     P -> Q | fail.
     

(For a definition of P -> Q | R, see ref-sem-con.)

-> cuts away any choice points in the execution of P

Note that the operator precedence of -> is greater than 1000, so it dominates commas. Thus, in:

     f :- p, q -> r, s.
     f.
     

-> cuts away any choices in p or in q, but unlike cut (!) it does not cut away the alternative choice for f.

Exceptions

context_error