Re: evaluation fault in ghci.

Curiously enough, this is a new bug.   The patch that fixed my previous 
problem does not solve this issue. 

I had a problem with derived Eq and Ord with a polymorphic representation of 
regular expressions.  Simon Peyton-Jones recently put a updated 
ghc/compiler/typecheck/TcGenDeriv.lhs in CVS,  FYI.

best,
leon

On Thursday 23 January 2003 11:01, Malcolm Wallace wrote:
> The interactive loop of ghci displays an interesting evaluation fault
> to do with derived equality.  In the attached source file, there is
> a simple guard which tests some equalities, and basically the same
> value is given on the left and right of the (==).  Yet, it evaluates
> to False in interactive mode, whereas it (correctly) evaluates to True
> when compiled.
>
>
> $ ghci
>    ___         ___ _
>   / _ \ /\  /\/ __(_)
>  / /_\// /_/ / /  | |      GHC Interactive, version 5.04.2, for Haskell 98.
> / /_\\/ __  / /___| |      http://www.haskell.org/ghc/
> \____/\/ /_/\____/|_|      Type :? for help.
>
> Loading package base ... linking ... done.
> Loading package haskell98 ... linking ... done.
> Prelude> :l Small
> Compiling Main             ( Small.hs, interpreted )
> Ok, modules loaded: Main.
> *Main> main
> "*** Exception: Four.bceFour: precondition fails:arrows not parallel
> f = E
> g = E
>
>
> $ ghc -o Small Small.hs
> $ ./Small
> "it works"
>
>
> I have verified that the fault exists at least as far back as 5.02.3.
>
> Regards,
>     Malcolm