GHC doesn't like its own type?

[oleg@pobox.com]

The previously message "Deeply uncurried products, as categorists
might like them" can be used to demonstrate certain behavior of GHC
that seems a bit odd. If we save the text of that message in a file,
/tmp/a.lhs, we can load it into GHC:

  $ ghci -fglasgow-exts /tmp/a.lhs
  GHC Interactive, version 5.04.1
  Ok, modules loaded: Main.
  *Main>

The whole code loads and typechecks. The code contains the following
definition, without an explicit type signature:

> fcomp a = (. fapp) (mcomp a)

We can ask GHCi to tell us the type of fcomp:

	*Main> :type fcomp
	forall result f1 a f2 c cp.
	(FApp a cp c, MCompose f2 cp c result) =>
	(f1 -> f2) -> a -> f1 -> result

and make that type, verbatim, to be the signature of fcomp:

> fcomp:: forall result f1 a f2 c cp. (FApp a cp c, MCompose f2 cp c result) => (f1 -> f2) -> a -> f1 -> result
> fcomp a = (. fapp) (mcomp a)

If we reload the file, we get an error:

/tmp/a.lhs:124:
    Could not deduce (FApp a cp c1)
        from the context (FApp a cp c, MCompose f2 cp c result)
    Probable fix:
        Add (FApp a cp c1) to the type signature(s) for `fcomp'
    arising from use of `fapp' at /tmp/a.lhs:124
    In the second argument of `(.)', namely `fapp'
    In the definition of `fcomp': (. fapp) (mcomp a)

/tmp/a.lhs:124:
    Could not deduce (MCompose f2 cp c1 result)
        from the context (FApp a cp c, MCompose f2 cp c result)
    Probable fix:
        Add (MCompose f2 cp c1 result) to the type signature(s) for `fcomp'
    arising from use of `mcomp' at /tmp/a.lhs:124
    In the first argument of `(. fapp)', namely `(mcomp a)'
    In the definition of `fcomp': (. fapp) (mcomp a)

I used to think that the inferred type is the most general type, and
that the compiler would accept as explicit the type that it itself
inferred. I was wrong?

The second odd circumstance is best illustrated by the following
transcript. Assume that /tmp/a.lhs is the text of the previous message
as it was posted:

 $  ghci -fglasgow-exts /tmp/a.lhs
 GHC Interactive, version 5.04.1, for Haskell 98.
 Loading package base ... linking ... done.
 Loading package haskell98 ... linking ... done.
 Compiling Main             ( /tmp/a.lhs, interpreted )

 /tmp/a.lhs:76: Warning: No 'main' defined in module Main
 Ok, modules loaded: Main.
 *Main> let x = \f -> fapp f (('a','b'),('c',('d','e')))
 Bus error (core dumped)

Incidentally, if I enter
> x = \f -> fapp f (('a','b'),('c',('d','e')))
into /tmp/a.lhs and load the file into GHCi, I get

ghc-5.04.1: panic! (the `impossible' happened, GHC version 5.04.1):
        rdrNameModule zddFApp