From: chak Date: Mon, 9 May 2005 13:25:07 +0000 (+0000) Subject: [project @ 2005-05-09 13:25:07 by chak] X-Git-Tag: Initial_conversion_from_CVS_complete~585 X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=33b563b5d9d9229dad0211fa8b85e0a5b2bd52f9;p=ghc-hetmet.git [project @ 2005-05-09 13:25:07 by chak] More details about type checking. --- diff --git a/ghc/docs/comm/the-beast/typecheck.html b/ghc/docs/comm/the-beast/typecheck.html index 2b9b553..e988062 100644 --- a/ghc/docs/comm/the-beast/typecheck.html +++ b/ghc/docs/comm/the-beast/typecheck.html @@ -14,7 +14,7 @@ GHC type checks programs in their original Haskell form before the desugarer converts them into Core code. This complicates the type checker as it has to handle the much more verbose Haskell AST, but it - improves error messages, as the those message are based on the same + improves error messages, as those message are based on the same structure that the user sees.

@@ -23,24 +23,117 @@ using a structure that abstracts over the concrete representation of bound occurences of identifiers and patterns. The module TcHsSyn - instantiates this structure for the type checker using TcRnTypes.TcId - to represent identifiers - in fact, a TcId is currently - nothing but just a synonym for a plain + used to represent identifiers in some signatures during type checking + is, in fact, nothing but a synonym for a plain Id.

+

The Overall Flow of Things

+

Entry Points Into the Type Checker

- The interface of the type checker (and renamer) to the rest of the - compiler is provided by renamer) to the rest of the compiler is provided + by TcRnDriver. Entire modules are processed by calling tcRnModule and GHCi - uses tcRnStmt and tcRnExpr to typecheck - statements and expressions, respectively. Moreover, - tcRnIface and tcRnExtCore are provided to - typecheck interface files and external Core code. + uses tcRnStmt, tcRnExpr, and + tcRnType to typecheck statements and expressions, and to + kind check types, respectively. Moreover, tcRnExtCore is + provided to typecheck external Core code. Moreover, + tcTopSrcDecls is used by Template Haskell - more + specifically by TcSplice.tc_bracket + - to type check the contents of declaration brackets. +

+ +

Renaming and Type Checking a Module

+

+ The function tcRnModule controls the complete static + analysis of a Haskell module. It sets up the combined renamer and type + checker monad, resolves all import statements, initiates the actual + renaming and type checking process, and finally, wraps off by processing + the export list. +

+

+ The actual type checking and renaming process is initiated via + TcRnDriver.tcRnSrcDecls, which uses a helper called + tc_rn_src_decls to implement the iterative renaming and + type checking process required by Template + Haskell. However, before it invokes tc_rn_src_decls, + it takes care of hi-boot files; afterwards, it simplifies type + constraints and zonking (see below regarding the later).

+

+ The function tc_rn_src_decls partitions static analysis of + a whole module into multiple rounds, where the initial round is followed + by an additional one for each toplevel splice. It collects all + declarations up to the next splice into an HsDecl.HsGroup + to rename and type check that declaration group by calling + TcRnDriver.tcRnGroup. Afterwards, it executes the + splice (if there are any left) and proceeds to the next group, which + includes the declarations produced by the splice. +

+

+ The function tcRnGroup, finally, gets down to invoke the + actual renaming and type checking via + TcRnDriver.rnTopSrcDecls and + TcRnDriver.tcTopSrcDecls, respectively. The renamer, apart + from renaming, computes the global type checking environment, of type + TcRnTypes.TcGblEnv, which is stored in the type checking + monad before type checking commences. +

+ +

Type Checking a Declaration Group

+

+ The type checking of a declaration group, performed by + tcTopSrcDecls starts by processing of the type and class + declarations of the current module, using the function + TcTyClsDecls.tcTyAndClassDecls. This is followed by a + first round over instance declarations using + TcInstDcls.tcInstDecls1, which in particular generates all + additional bindings due to the deriving process. Then come foreign + import declarations (TcForeign.tcForeignImports) and + default declarations (TcDefaults.tcDefaults). +

+

+ Now, finally, toplevel value declarations (including derived ones) are + type checked using TcBinds.tcTopBinds. Afterwards, + TcInstDcls.tcInstDecls2 traverses instances for the second + time. Type checking concludes with processing foreign exports + (TcForeign.tcForeignExports) and rewrite rules + (TcRules.tcRules). Finally, the global environment is + extended with the new bindings. +

+ +

Type checking Type and Class Declarations

+

+ Type and class declarations are type checked in a couple of phases that + contain recursive dependencies - aka knots. The first knot + encompasses almost the whole type checking of these declarations and + forms the main piece of TcTyClsDecls.tcTyAndClassDecls. +

+

+ Inside this big knot, the first main operation is kind checking, which + again involves a knot. It is implemented by kcTyClDecls, + which performs kind checking of potentially recursively-dependent type + and class declarations using kind variables for initially unknown kinds. + During processing the individual declarations some of these variables + will be instantiated depending on the context; the rest gets by default + kind * (during zonking of the kind signatures). + Type synonyms are treated specially in this process, because they can + have an unboxed type, but they cannot be recursive. Hence, their kinds + are inferred in dependency order. Moreover, in contrast to class + declarations and other type declarations, synonyms are not entered into + the global environment as a global TyThing. + (TypeRep.TyThing is a sum type that combines the various + flavours of typish entities, such that they can be stuck into type + environments and similar.) +

+ +

More Details

Types Variables and Zonking

@@ -208,7 +301,7 @@ tau -> tyvar

-Last modified: Sat Sep 13 23:35:24 BST 2003 +Last modified: Mon May 9 11:02:20 EST 2005