On 05/09/10 19:30, Ken Overton wrote:
I think, yes your function looks close to typical Haskell, you're just missing a "do", a pair of parentheses, and an "IO":
Sorry, I'd definitely intended the 'do' to be there.
interact :: String -> IO Resp
Thanks Isaac; so after I've called this how do I get the Resp value back out of the returned IO?
By using it in some other piece of IO. For example, main :: IO () main = do resp <- interact "hi there!" let modifiedResp = some function involving resp ... You see, "IO" lets you distinguish between functions/values that require IO actions, and those that are completely pure (always give the same result, given the same arguments, as is typical in mathematics). Just use your patience! : Every function that uses that resulting Resp will have to be in IO. This is not as bad as it seems, because most of the processing of the Resp can be pure again: for example, the way you call parseResp which is a pure function, or "some function involving resp" in my example above. i'd suggest 1. Practice. The typechecker will tell you when you get it wrong. 2. Generally try to mark less of your code as "IO", because this is good style ( -- it turns out to be easier to code [and refactor code] with pure functions, because you know they don't have side-effects, so you mostly don't need to worry about "when" or "how often" they're called.) -Isaac