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Error monad from Filinski's "Representing Monads"
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| ;; Error monad from Filinski's "Representing Monads" | |
| (define *default-prompt* (make-prompt)) | |
| (define (reflect m) (shift *default-prompt* k (ext k m))) | |
| (define (reify t) (push-prompt *default-prompt* (unit (t)))) | |
| (define-record-type Success | |
| (make-success a) | |
| success? | |
| (a get-success)) | |
| (define-record-type Error | |
| (make-error a) | |
| error? | |
| (a get-error)) | |
| (define (unit a) (make-success a)) | |
| (define (ext f m) | |
| (cond ((success? m) (f (get-success m))) | |
| ((error? m) m) | |
| (#t (fail "type error")))) | |
| (define (myraise e) (reflect (make-error e))) | |
| (define (myhandle t h) | |
| (let ((m (reify t))) | |
| (cond ((success? m) (get-success m)) | |
| ((error? m) (h (get-error m))) | |
| (#t (fail "type error"))))) | |
| (define (show t) | |
| (myhandle (lambda () (t)) | |
| (lambda (s) s))) | |
| (assert (= 3 (show (lambda () (+ 1 2))))) | |
| (assert (= #f (show (lambda () (+ 1 (+ 3 (myraise #f))))))) |
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