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diff --git a/docs/comm/the-beast/names.html b/docs/comm/the-beast/names.html deleted file mode 100644 index 061fae3ebf..0000000000 --- a/docs/comm/the-beast/names.html +++ /dev/null @@ -1,169 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN"> -<html> - <head> - <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"> - <title>The GHC Commentary - The truth about names: OccNames, and Names</title> - </head> - - <body BGCOLOR="FFFFFF"> - <h1>The GHC Commentary - The truth about names: OccNames, and Names</h1> - <p> - Every entity (type constructor, class, identifier, type variable) has a - <code>Name</code>. The <code>Name</code> type is pervasive in GHC, and - is defined in <code>basicTypes/Name.lhs</code>. Here is what a Name - looks like, though it is private to the Name module. - </p> - <blockquote> - <pre> -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 - }</pre> - </blockquote> - <ul> - <li> The <code>n_sort</code> field says what sort of name this is: see - <a href="#sort">NameSort below</a>. - <li> The <code>n_occ</code> field gives the "occurrence name" of the - Name; see - <a href="#occname">OccName below</a>. - <li> The <code>n_uniq</code> field allows fast tests for equality of - Names. - <li> The <code>n_loc</code> field gives some indication of where the - name was bound. - </ul> - - <h2><a name="sort">The <code>NameSort</code> of a <code>Name</code></a></h2> - <p> - There are four flavours of <code>Name</code>: - </p> - <blockquote> - <pre> -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')</pre> - </blockquote> - <ul> - <li>Here are the sorts of Name an entity can have: - <ul> - <li> Class, TyCon: External. - <li> Id: External, Internal, or System. - <li> TyVar: Internal, or System. - </ul> - </li> - <li>An <code>External</code> name has a globally-unique - (module name, occurrence name) pair, namely the - <em>original name</em> of the entity, - describing where the thing was originally defined. So for example, - if we have - <blockquote> - <pre> -module M where - f = e1 - g = e2 - -module A where - import qualified M as Q - import M - a = Q.f + g</pre> - </blockquote> - <p> - 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. - </p> - </li> - <li>An <code>InternalName</code> - has only an occurrence name. Distinct InternalNames may have the same - occurrence name; use the Unique to distinguish them. - </li> - <li>An <code>ExternalName</code> 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 - <code>InternalName</code> name can be cloned freely. - </li> - <li><strong>Before CoreTidy</strong>: the Ids that were defined at top - level in the original source program get <code>ExternalNames</code>, - whereas extra top-level bindings generated (say) by the type checker - get <code>InternalNames</code>. q This distinction is occasionally - useful for filtering diagnostic output; e.g. for -ddump-types. - </li> - <li><strong>After CoreTidy</strong>: An Id with an - <code>ExternalName</code> will generate symbols that - appear as external symbols in the object file. An Id with an - <code>InternalName</code> 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. - </li> - <li>A <code>System</code> name is for the most part the same as an - <code>Internal</code>. Indeed, the differences are purely cosmetic: - <ul> - <li>Internal names usually come from some name the - user wrote, whereas a System name has an OccName like "a", or "t". - Usually there are masses of System names with the same OccName but - different uniques, whereas typically there are only a handful of - distince Internal names with the same OccName. - </li> - <li>Another difference is that when unifying the type checker tries - to unify away type variables with System names, leaving ones with - Internal names (to improve error messages). - </li> - </ul> - </li> - </ul> - - <h2><a name="occname">Occurrence names: <code>OccName</code></a></h2> - <p> - An <code>OccName</code> is more-or-less just a string, like "foo" or - "Tree", giving the (unqualified) name of an entity. - </p> - <p> - 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 <tt>OccName</tt> (defined in - <tt>basicTypes/OccName.lhs</tt>) that is a pair of a <tt>FastString</tt> - and a <tt>NameSpace</tt> indicating which name space the name is drawn - from: - <blockquote> - <pre> -data OccName = OccName NameSpace EncodedFS</pre> - </blockquote> - <p> - The <tt>EncodedFS</tt> is a synonym for <tt>FastString</tt> indicating - that the string is Z-encoded. (Details in <tt>OccName.lhs</tt>.) - 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. - </p> - <p> - The name spaces are: - </p> - <ul> - <li> <tt>VarName</tt>: ordinary variables</li> - <li> <tt>TvName</tt>: type variables</li> - <li> <tt>DataName</tt>: data constructors</li> - <li> <tt>TcClsName</tt>: type constructors and classes (in Haskell they - share a name space) </li> - </ul> - - <small> -<!-- hhmts start --> -Last modified: Wed May 4 14:57:55 EST 2005 -<!-- hhmts end --> - </small> - </body> -</html> - |