Substantial improvements to coercion optimisation
The main purpose of this patch is to add a bunch of new rules to the coercion optimiser. They are documented in the (revised) Appendix of the System FC paper. Some code has moved about: - OptCoercion is now a separate module, mainly because it now uses tcMatchTy, which is defined in Unify, so OptCoercion must live higehr up in the hierarchy - Functions that manipulate Kinds has moved from Type.lhs to Coercion.lhs. Reason: the function typeKind now needs to call coercionKind. And in any case, a Kind is a flavour of Type, so it builds on top of Type; indeed Coercions and Kinds are both flavours of Type. This change required fiddling with a number of imports, hence the one-line changes to otherwise-unrelated modules - The representation of CoTyCons in TyCon has changed. Instead of an extensional representation (a kind checker) there is now an intensional representation (namely TyCon.CoTyConDesc). This was needed for one of the new coercion optimisations.
Showing with 910 additions and 710 deletions