Version 2 (modified by chak, 11 years ago) (diff)


Type Functions: Representation in Core and in Interfaces

Representation of type functions after type checking

Type functions have a number of properties in common with class instances; in particular, they require a machinery for matching type patterns against types, as instance heads do during context simplification. Hence, we probably want some structure similar to InstEnv.Instance for type functions - for instances this is maintained in the field iSpec of TcEnv.InstInfo (for type functions we don't need anything like iBinds as they are pure type-level entities). If possible, it would be ideal if we can reuse (or generalise) some of the matching machinery for instance heads.

The essentials of a module after type checking are in HscTypes.ModGuts; in particular, we have two fields mg_insts :: [Instance] and mg_binds :: [CoreRule] containing all instance heads and all rewrite rules respectively. Similarly, we now want something like mg_tyequa :: [TyEqua] to represent all type equations.

Refined idea: Instead of duplicating the InstInfo/Instance infrastructure for instances of indexed types, we could just add a second variant to InstInfo. This has the advantage that functions, such as tcInstDecls1, still only have to return a list of InstInfo and not two different lists.