[Haskell-cafe] Partially-applied type synonyms?

[Carl Witty]

On Tue, 2004-08-31 at 10:00, Chung-chieh Shan wrote:
> The rationale for disallowing matching partially-applied type synonyms
> is that higher-order unification is undecidable.

Higher-order unification is worse than just undecidable (after all,
GHC's extended Haskell already includes constructs which are
undecidable, which means that sometimes the compiler will loop forever);
it's ambiguous.  There can be multiple unifiers, none of which is the
most general.  See my earlier Haskell-cafe message for the trouble this
can cause (search for "<technical note>"):

	http://www.haskell.org/pipermail/haskell-cafe/2004-March/005965.html

Carl Witty