[Chicken-users] [ANN] Monad Egg

[Daniel Leslie]

I have written a small egg to ease the usage of lazily-evaluated monads.

For example, after defining the identity monad:

 (define-monad
   <id>
   (lambda (a) a)
   (lambda (a f) (f a)))

We can bind a chain of methods upon an initial value using it:

(doto-using <id> (+ 0 1)
  (lambda (x) (+ x 1))
  (lambda (y) (+ y 2)))

Or, alternatively, we can be explicit:

(using <id>
  (>>= (>>= (return (+ 0 1)) 
            (lambda (x) (+ x 1)))
       (lambda (y) (+ y 2))))

A short demo showing the behaviour:

#;1> (use monad)
#;2> (define m (doto-using <id> 1 (lambda (x) (display "Hi!\n") (+ x 1))))
#;3> m
Hi!
#<id> 2
#;4> m
#<id> 2
#;5> (define (m2 y) (doto-using <id> y (lambda (x) (display "Hi!\n") (+ x 1))))
#;6> (m2 1)
Hi!
#<id> 2
#;7> (m2 1)
Hi!
#<id> 2

The wiki has a fair amount of examples and documentation:
http://wiki.call-cc.org/eggref/4/monad

And the repository is on GitHub:

https://github.com/dleslie/monad-egg

Please have a look at the wiki for a more thorough introduction and comments.

Thanks for Chicken!

-Dan