[Haskell-cafe] What is <-

[Bulat Ziganshin]

Hello michael,

Sunday, August 8, 2010, 5:36:05 PM, you wrote:

i highly recommend you to read
http://sigfpe.blogspot.com/2006/08/you-could-have-invented-monads-and.html
that is the best introduction into monads i know

and then http://haskell.org/all_about_monads/html/index.html
- comprehensive tutorial about many useful monads

both are mentioned at http://en.wikipedia.org/wiki/Monad_%28functional_programming%29


> What is <- ? Couldn't find anything on Hoogle.

> 1)  main = do 
>       x <- getLine   -- get the value from the IO monad
>       putStrLn $ "You typed: " ++ x

> 2)  pythags = do
>       z <- [1..]     --get the value from the List monad?
>       x <- [1..z]
>       y <- [x..z]
>       guard (x^2 + y^2 == z^2)
>       return (x, y, z)



> From: http://en.wikibooks.org/wiki/Haskell/Syntactic_sugar

> Do and proc notation


>                       Sweet                                Unsweet
> Monadic binding  do x <- getLIne                      getLine >>= \x ->
>                     putStrLn $ "You typed: " ++  x     putStrLn $ "You typed: " ++ x


> So, Example 2 desugared becomes...

>      [1..] >== \z ->  ?





> Michael


>   


-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin at gmail.com