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diff --git a/docs/comm/the-beast/basicTypes.html b/docs/comm/the-beast/basicTypes.html new file mode 100644 index 0000000000..ca56d6b6a8 --- /dev/null +++ b/docs/comm/the-beast/basicTypes.html @@ -0,0 +1,132 @@ +<!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 Basics</title> + </head> + + <body BGCOLOR="FFFFFF"> + <h1>The GHC Commentary - The Basics</h1> + <p> + The directory <a + href="http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/ghc/compiler/basicTypes/"><code>fptools/ghc/compiler/basicTypes/</code></a> + contains modules that define some of the essential types definition for + the compiler - such as, identifiers, variables, modules, and unique + names. Some of those are discussed in the following. See elsewhere for more + detailed information on: + <ul> + <li> <a href="vars.html"><code>Var</code>s, <code>Id</code>s, and <code>TyVar</code>s</a> + <li> <a href="renamer.html"><code>OccName</code>s, <code>RdrName</code>s, and <code>Names</code>s</a> + </ul> + + <h2>Elementary Types</h2> + + <h4><code>Id</code>s</h4> + <p> + An <code>Id</code> (defined in <a + href="http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/ghc/compiler/basicTypes/Id.lhs"><code>Id.lhs</code></a> + essentially records information about value and data constructor + identifiers -- to be precise, in the case of data constructors, two + <code>Id</code>s are used to represent the worker and wrapper functions + for the data constructor, respectively. The information maintained in + the <code>Id</code> abstraction includes among other items strictness, + occurrence, specialisation, and unfolding information. + <p> + Due to the way <code>Id</code>s are used for data constructors, + all <code>Id</code>s are represented as variables, which contain a + <code>varInfo</code> field of abstract type <code><a + href="http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/ghc/compiler/basicTypes/IdInfo.lhs">IdInfo</a>.IdInfo</code>. + This is where the information about <code>Id</code>s is really stored. + The following is a (currently, partial) list of the various items in an + <code>IdInfo</code>: + <p> + <dl> + <dt><a name="occInfo">Occurence information</a> + <dd>The <code>OccInfo</code> data type is defined in the module <a + href="http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/ghc/compiler/basicTypes/BasicTypes.lhs"><code>BasicTypes.lhs</code></a>. + Apart from the trivial <code>NoOccInfo</code>, it distinguishes + between variables that do not occur at all (<code>IAmDead</code>), + occur just once (<code>OneOcc</code>), or a <a + href="simplifier.html#loopBreaker">loop breakers</a> + (<code>IAmALoopBreaker</code>). + </dl> + + <h2>Sets, Finite Maps, and Environments</h2> + <p> + Sets of variables, or more generally names, which are needed throughout + the compiler, are provided by the modules <a + href="http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/ghc/compiler/basicTypes/VarSet.lhs"><code>VarSet.lhs</code></a> + and <a + href="http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/ghc/compiler/basicTypes/NameSet.lhs"><code>NameSet.lhs</code></a>, + respectively. Moreover, frequently maps from variables (or names) to + other data is needed. For example, a substitution is represented by a + finite map from variable names to expressions. Jobs like this are + solved by means of variable and name environments implemented by the + modules <a + href="http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/ghc/compiler/basicTypes/VarEnv.lhs"><code>VarEnv.lhs</code></a> + and <a + href="http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/ghc/compiler/basicTypes/NameEnv.lhs"><code>NameEnv.lhs</code></a>. + + <h4>The Module <code>VarSet</code></h4> + <p> + The Module <code>VarSet</code> provides the types <code>VarSet</code>, + <code>IdSet</code>, and <code>TyVarSet</code>, which are synonyms in the + current implementation, as <code>Var</code>, <code>Id</code>, and + <code>TyVar</code> are synonyms. The module provides all the operations + that one would expect including the creating of sets from individual + variables and lists of variables, union and intersection operations, + element checks, deletion, filter, fold, and map functions. + <p> + The implementation is based on <a + href="http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/ghc/compiler/utils/UniqSet.lhs"><code>UniqSet</code></a>s, + which in turn are simply <a href="http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/ghc/compiler/utils/UniqFM.lhs"><code>UniqFM</code></a>s + (i.e., finite maps with uniques as keys) that map each unique to the + variable that it represents. + + <h4>The Module <code>NameSet</code></h4> + <p> + The Module <code>NameSet</code> provides the same functionality as + <code>VarSet</code> only for <a + href="http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/ghc/compiler/basicTypes/Name.lhs"><code>Name</code></a>s. + As for the difference between <code>Name</code>s and <code>Var</code>s, + a <code>Var</code> is built from a <code>Name</code> plus additional + information (mostly importantly type information). + + <h4>The Module <code>VarEnv</code></h4> + <p> + The module <code>VarEnv</code> provides the types <code>VarEnv</code>, + <code>IdEnv</code>, and <code>TyVarEnv</code>, which are again + synonyms. The provided base functionality is similar to + <code>VarSet</code> with the main difference that a type <code>VarEnv + T</code> associates a value of type <code>T</code> with each variable in + the environment, thus effectively implementing a finite map from + variables to values of type <code>T</code>. + <p> + The implementation of <code>VarEnv</code> is also by <a + href="http://cvs.haskell.org/cgi-bin/cvsweb.cgi/fptools/ghc/compiler/utils/UniqFM.lhs"><code>UniqFM</code></a>, + which entails the slightly surprising implication that it is + <em>not</em> possible to retrieve the domain of a variable environment. + In other words, there is no function corresponding to + <code>VarSet.varSetElems :: VarSet -> [Var]</code> in + <code>VarEnv</code>. This is because the <code>UniqFM</code> used to + implement <code>VarEnv</code> stores only the unique corresponding to a + variable in the environment, but not the entire variable (and there is + no mapping from uniques to variables). + <p> + In addition to plain variable environments, the module also contains + special substitution environments - the type <code>SubstEnv</code> - + that associates variables with a special purpose type + <code>SubstResult</code>. + + <h4>The Module <code>NameEnv</code></h4> + <p> + The type <code>NameEnv.NameEnv</code> is like <code>VarEnv</code> only + for <code>Name</code>s. + + <p><hr><small> +<!-- hhmts start --> +Last modified: Tue Jan 8 18:29:52 EST 2002 +<!-- hhmts end --> + </small> + </body> +</html> |