- Every entity (type constructor, class, identifier, type variable) has a
- Name. The Name type is pervasive in GHC, and
- is defined in basicTypes/Name.lhs. Here is what a Name
- looks like, though it is private to the Name module.
-
-
-data Name = Name {
- n_sort :: NameSort, -- What sort of name it is
- n_occ :: !OccName, -- Its occurrence name
- n_uniq :: Unique, -- Its identity
- n_loc :: !SrcLoc -- Definition site
- }
-
- n_sort field says what sort of name this is: see
- NameSort below.
- n_occ field gives the "occurrence name" of the
- Name; see
- OccName below.
- n_uniq field allows fast tests for equality of
- Names.
- n_loc field gives some indication of where the
- name was bound.
- NameSort of a Name
- There are four flavours of Name:
-
---data NameSort - = External Module (Maybe Name) - -- (Just parent) => this Name is a subordinate name of 'parent' - -- e.g. data constructor of a data type, method of a class - -- Nothing => not a subordinate - - | WiredIn Module (Maybe Name) TyThing BuiltInSyntax - -- A variant of External, for wired-in things - - | Internal -- A user-defined Id or TyVar - -- defined in the module being compiled - - | System -- A system-defined Id or TyVar. Typically the - -- OccName is very uninformative (like 's')-
External name has a globally-unique
- (module name, occurrence name) pair, namely the
- original name of the entity,
- describing where the thing was originally defined. So for example,
- if we have
- ---module M where - f = e1 - g = e2 - -module A where - import qualified M as Q - import M - a = Q.f + g-
- then the RdrNames for "a", "Q.f" and "g" get replaced (by the - Renamer) by the Names "A.a", "M.f", and "M.g" respectively. -
-InternalName
- has only an occurrence name. Distinct InternalNames may have the same
- occurrence name; use the Unique to distinguish them.
- ExternalName has a unique that never changes. It
- is never cloned. This is important, because the simplifier invents
- new names pretty freely, but we don't want to lose the connnection
- with the type environment (constructed earlier). An
- InternalName name can be cloned freely.
- ExternalNames,
- whereas extra top-level bindings generated (say) by the type checker
- get InternalNames. q This distinction is occasionally
- useful for filtering diagnostic output; e.g. for -ddump-types.
- ExternalName will generate symbols that
- appear as external symbols in the object file. An Id with an
- InternalName cannot be referenced from outside the
- module, and so generates a local symbol in the object file. The
- CoreTidy pass makes the decision about which names should be External
- and which Internal.
- System name is for the most part the same as an
- Internal. Indeed, the differences are purely cosmetic:
- OccName
- An OccName is more-or-less just a string, like "foo" or
- "Tree", giving the (unqualified) name of an entity.
-
- Well, not quite just a string, because in Haskell a name like "C" could - mean a type constructor or data constructor, depending on context. So - GHC defines a type OccName (defined in - basicTypes/OccName.lhs) that is a pair of a FastString - and a NameSpace indicating which name space the name is drawn - from: -
---data OccName = OccName NameSpace EncodedFS-
- The EncodedFS is a synonym for FastString indicating - that the string is Z-encoded. (Details in OccName.lhs.) - Z-encoding encodes funny characters like '%' and '$' into alphabetic - characters, like "zp" and "zd", so that they can be used in object-file - symbol tables without confusing linkers and suchlike. -
-- The name spaces are: -
-