Re: [Haskell-cafe] howto mix <- within do?

17 Oct 2008

      On Fri, Oct 17, 2008 at 1:39 PM, Larry Evans  wrote:
...
do_with_assignment.proto.hs:30:2:
   Couldn't match expected type `[]' against inferred type `IO'
     Expected type: [t]
     Inferred type: IO ()
   In the expression: putStr "v0="
   In a 'do' expression: putStr "v0="
Prelude> let f = do { v <- [999] ; return () }
Prelude> :t f
f :: [()]
Prelude> :t putStr ""
putStr "" :: IO ()

So "v <- [999]" is in the list monad, but putStr is in the IO monad.
The two cannot mix in that way.

This looks like it might be homework so I'll refrain from saying any
more for now. Good luck!

D

Re: [Haskell-cafe] howto mix <- within do?

Dougal Stanton