functional programming - Use of Underscore in Scala -


why works?

def exists(s: set, p: int => boolean): boolean = { forall(s, !p(_)) }

and doesn't?

def exists(s: set, p: int => boolean): boolean = { forall(s, !p()) }

where forall function, , p predicate.

the call predicate expecting parameter passed, can't call without passing (which p() doing).

the underscore kind of scala short-hand "the current value", value int passed p. if explicitly label int i, de-sugars to:

{ forall(s, (i: int) => !p(i)) }

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