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;; (read-enable 'curly-infix)
;;; Examples:
;;; These are do in the conext of the optional monad.
(add-to-load-path (dirname (current-filename)))
(use-modules (control monad)
(data monoid)
(data optional)
(data writer))
(do (just x) <- (just 10)
x) ; => 10
(do let y = (just 10)
(just x) <- y
(+ x 5)) ; => 15
(do (just x) <- (nothing)
(+ x 5)) ; => [Nothing]
;;;
(do let either = left 10
(left x) <- either
x) ; EVALUATION ERROR
;; Int -> Writer Int String
(define (log-number n)
(writer n (format #f "Got nuber: ~a" n)))
(define (mult-with-log)
(do (writer a) <- (log-number 3)
(writer b) <- (log-number 5)
(* a b)))
(do (writer a) <- (log-number 1)
a) ; EVALUATION ERROR
(begin { (log-number 1) >>= log-number })
;; => [Writer 1, "Got nuber: 1, Got nuber: 1"]
(do (writer a) <- (log-number 3)
(writer b) <- (log-number 5)
(writer (* a b) ""))
;; EVALUATION ERROR
;; => [Writer 3, "Got nuber: 3, base"]
(log-number 3) ; => [Writer 3, "Got nuber: 3"]
(just 1) ; => [Just 1]
(do let y = 5
(just x) <- (just 10)
(just (* x y)))
;; => [Just 50]
;;; TODO
;;; '<- and 'let can't be used after '<-
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