[Haskell] Perhaps a bug in GHC 6.10

[Eric Walkingshaw]

It looks like the 6.10 behavior is actually the correct one:

http://www.mail-archive.com/glasgow-haskell-bugs@haskell.org/msg13632.html

Also, see the do-notation translation section in the Haskell 98 Report:

http://www.haskell.org/onlinereport/exps.html#sect3.14

-Eric

On Wed, Dec 3, 2008 at 5:45 AM, Krasimir Angelov <kr.angelov at gmail.com> wrote:
> Hi,
>
> One of my students wrote code like this:
>
>
> prop_blank s (i,j) li =
>  if i==li
>    then
>       do if something then True else False
>    else
>       prop_blank (...) (i,j) (li+1)
>
>
> This code is not accepted from GHC 6.8.3 because Bool is not a monad.
> In particular the error message is:
>
> Sudoku.hs:269:5:
>    Couldn't match expected type `Bool' against inferred type `a b'
>    In the expression:
>          ......
>
> Surprisingly the same code is accepted from GHC 6.10. This looks like
> a bug for me. The easiest way to reproduce this is to try to evaluate:
>
>> do True
>
> in GHCi with GHC 6.8.3 and with GHC 6.10
>
> Is there any reason to accept this code?
>
>
> Regards,
>  Krasimir
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