Re: [Haskell-beginners] Type error in sub-function

23 Jul 2014


      On 7/23/2014 3:08 PM, 양철웅 wrote:
Look at the error:
...
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 }
Rewriting that do-block a little, we get:
do utcTime <- currentUTCTime
   problem
 where problem = formatTime defaultTimeLocale "%a" utcTime
In plain English, GHC's error message means:
...
On line 21 of test.hs, column 57:
     I (GHC) inferred from the context surrounding it that
     'problem' should have the type 'IO a' for some a.
     However, you defined 'problem' in a way that makes its
     type be 'String'. Therefore, I can't accept your program.
Do you see what caused the error?
How would you fix it?
HTH,
Gesh