[Haskell-beginners] Type error in sub-function

23 Jul 2014

      Hi, all!

When I compile my program below, ghc emits Type error.
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.
What am I missing?
Any comments are appreciated.

Thanks in advance!

Chul-Woong
-- 

import Data.Time.LocalTime      (getZonedTime, zonedTimeToUTC)
import System.Locale            (defaultTimeLocale)
import Data.Time.Format         (formatTime)
import Data.Time.Clock         (UTCTime)

currentUTCTime :: IO UTCTime
currentUTCTime = do
zTime <- getZonedTime
        return (zonedTimeToUTC zTime)

fooFunc :: IO String
fooFunc = do
  putStrLn "Hello, world"
  barFunc "xutc"
      where barFunc s =
                case s of
                  "apple" -> return s
                  ('x': val) -> return timedVal
                       where timedVal = case val of
                                            "utc" -> do utcTime <-
currentUTCTime
                                                        formatTime
defaultTimeLocale "%a" utcTime
---
Prelude> :l test
[1 of 1] Compiling Main             ( test.hs, interpreted )

test.hs:21:57:
    Couldn't match expected type `IO b0' with actual type `String'
    In the return type of a call of `formatTime'
    In a stmt of a 'do' block:
      formatTime defaultTimeLocale "%a" utcTime
    In the expression:
      do { utcTime <- currentUTCTime;
           formatTime defaultTimeLocale "%a" utcTime }

[Haskell-beginners] Type error in sub-function

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