Not every invocation of forsome calls find_i. It calls p(find_i(...)), but p can return a value without actually evaluating the inner find_i. So yeah, it relies on laziness, though you can translate it into a strict language by inserting lambdas in a bunch of places.

Thank you. How does Haskell manage to avoid evaluating find_i(...) before invoking p? Since the inner value is the argument to p, it's hard to imagine how p can do anything until it has that value.

EDIT: I think I see the light. The result of find_i(...) is not what's sent to p. Instead, Haskell passes a thunk that might never need to be evaluated.

Exactly. If I write

    let f x = 1

    print (f (g somethingelse))

then the call to g is never evaluated. f returns 1 immediately.