[racket] Little Schemer, lat?
I was surprised that *cdr* upsets the type-checker? How to fix?
#lang typed/racket
(: atom? (-> Any Boolean))
(define (atom? a)
(or (symbol? a) (boolean? a) (number? a) (string? a)))
(: lat? (-> (List Any) Boolean))
(define (lat? l)
(cond
[(null? l) #t]
[(atom? (car l)) (lat? (cdr l))]
[else #f]))
Type Checker: Polymorphic function `cdr' could not be applied to arguments:
Types: (Pairof a b) -> (b : ((! False @ (cdr) (0 0)) | (False @ (cdr) (0
0))) : (cdr (0 0)))
(Listof a) -> (Listof a)
Arguments: (List Any)
Expected result: (List Any)
in: (cdr l)
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