|Version 2 (modified by simonpj, 10 years ago) (diff)|
[ Up: Commentary/Compiler/HscMain ]
RdrNames and OccNames
When the parser parses an identifier, it generates a RdrName. A RdrName is pretty much just a string, or a pair of strings, for a qualified name, such as M.x. Here's the data type declaration, from compiler/basicTypes/RdrName.lhs:
data RdrName = Unqual OccName -- Used for ordinary, unqualified occurrences | Qual ModuleName OccName -- A qualified name written by the user in -- *source* code. The module isn't necessarily -- the module where the thing is defined; -- just the one from which it is imported | Orig Module OccName -- An original name; the module is the *defining* module. -- This is used when GHC generates code that will be fed -- into the renamer (e.g. from deriving clauses), but where -- we want to say "Use Prelude.map dammit". | Exact Name -- We know exactly the Name. This is used -- (a) when the parser parses built-in syntax like "" -- and "(,)", but wants a RdrName from it -- (b) when converting names to the RdrNames in IfaceTypes -- Here an Exact RdrName always contains an External Name -- (Internal Names are converted to simple Unquals) -- (c) by Template Haskell, when TH has generated a unique name
A ModuleName is just a FastString (see compiler/basicTypes/Module.lhs). But OccName is more interesting; next section.
The OccName type
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. The data type is defined (abstractly) in compiler/basicTypes/OccName.lhs:
data OccName = OccName NameSpace EncodedFS
The EncodedFS is a synonym for FastString indicating that the string is Z-encoded. (Details in compiler/basicTypes/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:
data NameSpace = VarName -- Variables, including "source" data constructors | DataName -- "Real" data constructors | TvName -- Type variables | TcClsName -- Type constructors and classes; Haskell has them -- in the same name space for now.