compiler/backpack/NameShape.hs¶
Note [NameShape]¶
When we write a declaration in a signature, e.g., data T, we ascribe to it a name variable, e.g., {m.T}. This name variable may be substituted with an actual original name when the signature is implemented (or even if we merge the signature with one which reexports this entity from another module).
When we instantiate a signature m with a module M, we also need to substitute over names. To do so, we must compute the name substitution induced by the exports of the module in question. A NameShape represents such a name substitution for a single module instantiation. The “shape” in the name comes from the fact that the computation of a name substitution is essentially the shaping pass from Backpack‘14, but in a far more restricted form.
The name substitution for an export list is easy to explain. If we are filling the module variable <m>, given an export N of the form M.n or {m’.n} (where n is an OccName), the induced name substitution is from {m.n} to N. So, for example, if we have A=impl:B, and the exports of impl:B are impl:B.f and impl:C.g, then our name substitution is {A.f} to impl:B.f and {A.g} to impl:C.g
The ‘NameShape’ type is defined in TcRnTypes, because TcRnTypes needs to refer to NameShape, and having TcRnTypes import NameShape (even by SOURCE) would cause a large number of modules to be pulled into the DynFlags cycle. data NameShape = NameShape {
ns_mod_name :: ModuleName, ns_exports :: [AvailInfo], ns_map :: OccEnv Name}
NB: substitution functions need ‘HscEnv’ since they need the name cache to allocate new names if we change the ‘Module’ of a ‘Name’
