I'm trying to create a polymorphic type for `flatten` that reflects its usual behavior.
This monomorphic version works: #lang typed/racket/base (require/typed rackunit [check-equal? (Any Any . -> . Any)]) (require/typed racket/list [flatten (All (A) (Rec as (U Integer (Listof as))) -> (Listof Integer))]) (define flatten-integers (inst flatten Integer)) (check-equal? (flatten-integers 1) '(1)) (check-equal? (flatten-integers '(1)) '(1)) (check-equal? (flatten-integers '(1 (2 3) 4)) '(1 2 3 4)) (check-equal? (flatten-integers '(1 (2 3 (4 5)) 6)) '(1 2 3 4 5 6)) But when I try to substitute the polymorphic type `A` for `Integer`, it stops working: #lang typed/racket/base (require/typed rackunit [check-equal? (Any Any . -> . Any)]) (require/typed racket/list [flatten (All (A) (Rec as (U A (Listof as))) -> (Listof A))]) (define flatten-integers (inst flatten Integer)) (check-equal? (flatten-integers 1) '(1)) (check-equal? (flatten-integers '(1)) '(1)) (check-equal? (flatten-integers '(1 (2 3) 4)) '(1 2 3 4)) (check-equal? (flatten-integers '(1 (2 3 (4 5)) 6)) '(1 2 3 4 5 6)) > git/racket/racket/collects/racket/contract/private/blame.rkt:143:0: flatten: > contract violation; none of the branches of the or/c matched Is it possible? If so, what am I missing? ____________________ Racket Users list: http://lists.racket-lang.org/users
