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(add-to-load-path (dirname (current-filename)))
(use-modules (control monad)
(data monoid)
(data optional)
(data writer))
;;; Optional Monad, and do notation
(do x <- (just 10)
x) ; => 10
(do let y = (just 10)
x <- y
(+ x 5)) ; => 15
(do x <- (nothing)
(+ x 5)) ; => [Nothing]
(do x <- (just 10)
y <- (just 20)
(+ x y)) ; => 30
;;; Writer Monad, and do notation
;; Int -> Writer Int String
(define (log-number n)
(writer n (format #f "Got nuber: ~a" n)))
(do a <- (log-number 3)
b <- (log-number 5)
(writer (* a b) ""))
;; => [Writer 15, "Got nuber: 3, Got nuber: 5, "]
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