simple putStrLn in Haskell/Yampa with arrows syntax

Posted by sisif on Stack Overflow See other posts from Stack Overflow or by sisif
Published on 2010-06-01T06:28:26Z Indexed on 2010/06/01 6:33 UTC
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Filed under:

beginner

|

haskell

|

arrows

|

FRP

i'm using Haskell with the Yampa FRP library which uses the arrows language extension.

how can i do a simple putStrLn in a SF?

mySF = proc x -> do
    y <- identity -< x*x
    putStrLn "Hello World!" ++ show y
    returnA -< y

the arrow syntax complains about the expression not bein an arrow (of course), but even with arrows i get no output

 output <- identity -< putStrLn "Hello World!"

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