[Haskell-beginners] Type error in sub-function

[Kim-Ee Yeoh]

On Wed, Jul 23, 2014 at 7:08 PM, 양철웅 <cwyang at aranetworks.com> wrote:

> Since the return type of foo Func is IO String and
> first case statement has "return timedVal",
> I think that ghc expects the type of timedVal as String.
> However, the error message shows that
> ghc expects timedVal should have type IO b0.
>

It's not really about timedVal nor the case 'statement'. (The scare quotes
are because there are only expressions, not statements, in haskell.)

Consider the difference between

do { putStrLn "hello"; True; }

and

do { putStrLn "hello"; return True; }

Which one throws an error and why?


-- Kim-Ee
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