It's quite possible that this is Eli's bug again, but boy this causes
headaches:
> Type Checker: parse error in type;
> type variable must be used with ...
> variable: Y in: Y
And it points precisely to where Y is followed by ...
#lang typed/racket
(module+ test (require rackunit))
;; [Listof X] [X [Listof X] Y ... -> Y ...] Y ... -> Y ...
(: foldl* (All (X Y ...) (->* [Listof X] [->* X Y ... (Values Y ...)] Y ...
(Values Y ...))))
(define (foldl* l f e1 . es)
(define e+ (cons e1 es))
(cond
[(empty? l) (apply values e+)]
[else (call-with-values
(lambda () (apply f (first l) e+))
(lambda e*
(unless (cons? e*) ;; should I check that (= (length e*) (length
e+))
(error 'fold* "f produced too few values: ~e" e*))
(apply foldl* (rest l) f e*)))]))
(module+ test
(define distances '(50 40 70 30 30))
(check-equal?
(call-with-values
(lambda ()
(foldl* distances
(lambda (fst distance distance*)
(values (+ fst distance) (cons (+ fst distance) distance*)))
0
'()))
(lambda (_ x)
(reverse x)))
'(50 90 160 190 220)))
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