Re: [Haskell-cafe] Can type be changed along a >>= chain?

I hope you're not building some unneeded "rules" in your head. There is no reason to believe there is something to be remembered about whether or not "types can change along a >>= chain". That chain has nothing special in Haskell. >>= is just an operator, much like ++, ! or . ghci> :t (>>=) (>>=) :: (Monad m) => m a -> (a -> m b) -> m b This says that, you provide an a and you get a b. Nothing says the a and b have to be the same upon successive uses. Likewise, ghci> :t (+) (+) :: (Num a) => a -> a -> a fromIntegral ((1 :: Int) + 2) + (3 :: Integer) 6 This shows clearly that the types are not the same along the "+ chain". 2009/10/12 michael rice

Dumb! I just figured out I was entering the input string in quotes.

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= chain. I was having trouble doing it in a different problem, created

So, I suppose the answer to my question is yes, type CAN be changed along a this small example to illustrate the problem, and then screwed it up putting quotes around my input string.

Thanks!

Michael

--- On *Mon, 10/12/09, Niklas Broberg * wrote:

From: Niklas Broberg Subject: Re: [Haskell-cafe] Can type be changed along a >>= chain? To: "michael rice" Cc: haskell-cafe@haskell.org Date: Monday, October 12, 2009, 12:43 PM

On Mon, Oct 12, 2009 at 6:37 PM, michael rice http://mc/compose?to=nowgate@yahoo.com

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wrote:

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transform :: IO () transform = putStrLn "What is your digit string?" >> getLine >>= \str -> return ('9':str) >>= \str -> return (read str :: Int) >>= \i -> putStrLn $ "The number is " ++ show i

This code works perfectly for me. What problem are you seeing specifically? Cheers, /Niklas

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