Re: [Haskell-beginners] lazy mapM

Thanks. Since this is an exercise I would be really curious what is the idiomatic Haskell approach. On Mon, Apr 1, 2013 at 3:29 AM, Kim-Ee Yeoh wrote:

On Mon, Apr 1, 2013 at 6:26 AM, Ovidiu D wrote:

...

1. Make f behave lazy Its input list is made of lines read from stdin and I want it to process lines one by one as they are entered by the user.

Eschewing laziness (which adds only complexity in this case), here's something that'll work, if a little ugly:

import System.Exit

f :: String -> IO () f "exit" = exitSuccess f a = putStrLn $ "you entered: " ++ a

main = do s <- getLine f s main

Going down this path would involve IORef's, among others from the "sin bin".

Something more pure and haskell-y would typically involve an analysis of the DSL abstract syntax and state space and implementation using a combination of State and Free monads.

-- Kim-Ee

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