I'm finding it difficult to construct filters for given types: #lang typed/racket
(define-type GradeElement
(Pair Bytes Null))
(: grade-element? (Any -> Boolean : GradeElement))
(define (grade-element? a)
(and (pair? a)
(bytes? (car a))
(null? (cdr a))))
=>
Type Checker: Expected result with filter ((GradeElement @ a) | (! GradeElement
@ a)), got filter ((AndFilter (Bytes @ (car) a) ((Pairof Any Any) @ a) (Null @
(cdr) a)) | (OrFilter (! Null @ (cdr) a) (! Bytes @ (car) a) (! (Pairof Any
Any) @ a))) in: (and (pair? a) (bytes? (car a)) (null? (cdr a)))
I admit that that error just makes my eyes glaze over, but I'm pretty sure that
the problem here is that TR can't reduce this filter type, and just needs a
cleverness injection.
Looking at this, though, it seems to me that it might be simpler just to ask TR
to construct a filter for a given type, and it occurs to me that this might
already be built-in. If so, I can't find it in the documentation.
John
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