evaluation fault in ghci.

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

Small.hs
Description: Text document