[Haskell] Should the following program be accepted by ghc?

[Simon Peyton-Jones]

| I have been playing with ghc6.8.1 and type families and the following
| program is accepted without any type-checking error:

Martin's comments are spot on.

FWIW, in the HEAD -- as Stefan says, type families are not *supposed* to work in 6.8.1 -- your program gives

TF.hs:9:7:
    Couldn't match expected type `a' against inferred type `b'
      `a' is a rigid type variable bound by
          the type signature for `c' at TF.hs:8:7
      `b' is a rigid type variable bound by
          the type signature for `c' at TF.hs:8:15
      Expected type: a :=: b
      Inferred type: b :=: b
    In the expression: Eq
    In the definition of `c': c Eq = Eq

That's fair enough.  If you change K to be a 'data family', then decomposition works, and the program compiles.

Bugs in type families against the HEAD are, as Don says, highly welcome.

Simon