wiki:TypeFunctionsIface

Version 6 (modified by chak, 8 years ago) (diff)

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Type Functions: Interface

Representation of family instances

The IfaceSyn.IfaceData variant of IfaceDecl contains a new ifFamInst :: Maybe IfaceFamInst field that is distinguishes ordinary data/newtype declarations from family instances. In the latter case, a IfaceFamInst value gives the instances head of the family instance. Moreover, all family instance heads of a module are collected in the new mi_fam_insts :: [(IfaceFamInst, IfaceDecl)] field of HscTypes.ModIface. We don't include the IfaceDecl component into IfaceFamInst, as we otherwise would get a cyclic dependency - the IfaceDecl must include IfaceFamInst, so that we can generate the correct wrapper signature for family data constructors during type checking the interface declarations.

The mi_fam_insts field does not contain any additional information, but instead is just a cached summary of the family instances of the mi_decls field. Hence, the serialised interface description does not explicitly contain the value of mi_fam_insts. Instead, the get method of Binary ModIface (in BinIface) - like all other places producing a HscTypes.ModIface - uses HscTypes.mkIfaceFamInstsCache to extract the relevant information from the declarations.

Similarly, HscTypes.ModDetails maintains a cached summary of the type checked representations of family instances in md_fam_insts :: ![FamInstEnv.FamInst]. This computed from teh field md_types with HscTypes.mkDetailsFamInstsCache.