[ ghc-Bugs-1156554 ] GHCi: No instance for (Show (IO ()))

Bugs item #1156554, was opened at 2005-03-04 10:03
Message generated for change (Settings changed) made by simonpj
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Category: GHCi
Group: 6.4
>Status: Closed
>Resolution: Fixed
Priority: 4
Submitted By: Simon Marlow (simonmar)
Assigned to: Nobody/Anonymous (nobody)
Summary: GHCi: No instance for (Show (IO ()))

Initial Comment:
>From Wolfgang Thaller:

This behaviour (from today's stable branch) is slightly
confusing:

> Prelude> print id
>
> Top level:
>     No instance for (Show (IO ()))
>       arising from use of `print' at Top level
>     Probable fix: add an instance declaration for
(Show (IO ()))
>     In a 'do' expression: print it
>
> <interactive>:1:0:
>     No instance for (Show (a -> a))
>       arising from use of `print' at <interactive>:1:0-4
>     Probable fix: add an instance declaration for
(Show (a -> a))
>     In the definition of `it': it = print id

The second message makes sense, but the first one
doesn't. Also, what's 
the difference between "Top level" and "<interactive>:1:0"?



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>Comment By: Simon Peyton Jones (simonpj)
Date: 2005-05-20 12:31

Message:
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Finally fixed.


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Comment By: Simon Marlow (simonmar)
Date: 2005-04-29 09:52

Message:
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Futher to this bug report, here's another expression that
gives a terrible error message:

Prelude Random> randomRIO (1,2)

Top level:
    No instance for (Show (IO a))
      arising from use of `print' at Top level
    Probable fix: add an instance declaration for (Show (IO a))
    In a 'do' expression: print it


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You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=108032&aid=1156554&group_id=8032