-%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1995
+
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[MatchCon]{Pattern-matching constructors}
\begin{code}
+module MatchCon ( matchConFamily ) where
+
#include "HsVersions.h"
-module MatchCon (
- matchConFamily
-) where
-
-import AbsSyn -- the stuff being desugared
-import PlainCore -- the output of desugaring;
- -- importing this module also gets all the
- -- CoreSyn utility functions
-import DsMonad -- the monadery used in the desugarer
-
-import AbsUniType ( mkTyVarTy, splitType, TyVar, TyVarTemplate,
- getTyConDataCons,
- instantiateTauTy, TyCon, Class, UniType,
- TauType(..), InstTyEnv(..)
- IF_ATTACK_PRAGMAS(COMMA instantiateTy)
- )
+import {-# SOURCE #-} Match ( match )
+
+import HsSyn ( OutPat(..) )
+
+import DsMonad
import DsUtils
-import Id ( eqId, getInstantiatedDataConSig,
- getIdUniType, isDataCon, DataCon(..)
- )
-import Maybes ( Maybe(..) )
-import Match ( match )
-import Util
-\end{code}
-\subsection[matchConFamily]{Making alternatives for a constructor family}
+import Id ( Id )
+import CoreSyn
+import Type ( mkTyVarTys )
+import ListSetOps ( equivClassesByUniq )
+import Unique ( Uniquable(..) )
+\end{code}
We are confronted with the first column of patterns in a set of
equations, all beginning with constructors from one ``family'' (e.g.,
@[]@ and @:@ make up the @List@ ``family''). We want to generate the
-alternatives for a @CoCase@ expression. There are several choices:
+alternatives for a @Case@ expression. There are several choices:
\begin{enumerate}
\item
Generate an alternative for every constructor in the family, whether
chapter does.
\begin{description}
\item[Advantages:]
-(a)~Simple. (b)~It may also be that large sparsely-used constructor families are mainly
-handled by the code for literals.
+(a)~Simple. (b)~It may also be that large sparsely-used constructor
+families are mainly handled by the code for literals.
\item[Disadvantages:]
-(a)~Not practical for large sparsely-used constructor families, e.g., the
-ASCII character set. (b)~Have to look up (in the TDE environment) a
-list of what constructors make up the whole family. So far, this is
-the only part of desugaring that needs information from the environments.
+(a)~Not practical for large sparsely-used constructor families, e.g.,
+the ASCII character set. (b)~Have to look up a list of what
+constructors make up the whole family.
\end{description}
\item
\end{description}
\end{enumerate}
-We are implementing the ``do-it-right'' option for now.
-The arguments to @matchConFamily@ are the same as to @match@; the extra
-@Int@ returned is the number of constructors in the family.
+We are implementing the ``do-it-right'' option for now. The arguments
+to @matchConFamily@ are the same as to @match@; the extra @Int@
+returned is the number of constructors in the family.
The function @matchConFamily@ is concerned with this
-have-we-used-all-the-constructors question; the local function
+have-we-used-all-the-constructors? question; the local function
@match_cons_used@ does all the real work.
\begin{code}
matchConFamily :: [Id]
-> [EquationInfo]
- -> [EquationInfo] -- Shadows
-> DsM MatchResult
-matchConFamily (var:vars) eqns_info shadows
- = match_cons_used vars eqns_info shadows `thenDs` \ alts ->
- mkCoAlgCaseMatchResult var alts
-\end{code}
+matchConFamily (var:vars) eqns_info
+ = let
+ -- Sort into equivalence classes by the unique on the constructor
+ -- All the EqnInfos should start with a ConPat
+ eqn_groups = equivClassesByUniq get_uniq eqns_info
+ get_uniq (EqnInfo _ _ (ConPat data_con _ _ _ _ : _) _) = getUnique data_con
+ in
+ -- Now make a case alternative out of each group
+ mapDs (match_con vars) eqn_groups `thenDs` \ alts ->
-And here is the local function that does all the work. It is more-or-less the
-@matchCon@/@matchClause@ functions on page~94 in Wadler's chapter in SLPJ.
-\begin{code}
-match_cons_used _ [{- no more eqns -}] _ = returnDs []
+ returnDs (mkCoAlgCaseMatchResult var alts)
+\end{code}
-match_cons_used vars eqns_info@(EqnInfo (ConPat data_con _ arg_pats : ps1) _ : eqns) shadows
- = ASSERT(isDataCon data_con)
- let
- (eqns_for_this_con, eqns_not_for_this_con) = splitByCon eqns_info
- (shadows_for_this_con, shadows_not_for_this_con) = splitByCon shadows
- in
- -- Go ahead and do the recursive call to make the alts
- -- for the other ConPats in this con family...
- match_cons_used vars eqns_not_for_this_con shadows_not_for_this_con `thenDs` \ rest_of_alts ->
+And here is the local function that does all the work. It is
+more-or-less the @matchCon@/@matchClause@ functions on page~94 in
+Wadler's chapter in SLPJ.
- -- Make new vars for the con arguments; avoid new locals where possible
- selectMatchVars arg_pats `thenDs` \ new_vars ->
+\begin{code}
+match_con vars all_eqns@(EqnInfo n ctx (ConPat data_con _ ex_tvs ex_dicts arg_pats : pats1) match_result1 : other_eqns)
+ = -- Make new vars for the con arguments; avoid new locals where possible
+ mapDs selectMatchVar arg_pats `thenDs` \ arg_vars ->
-- Now do the business to make the alt for _this_ ConPat ...
- match (new_vars++vars)
- (map shift_con_pat eqns_for_this_con)
- (map shift_con_pat shadows_for_this_con) `thenDs` \ match_result ->
-
- returnDs (
- (data_con, new_vars, match_result)
- : rest_of_alts
- )
- where
- splitByCon :: [EquationInfo] -> ([EquationInfo], [EquationInfo])
- splitByCon [] = ([],[])
- splitByCon (info@(EqnInfo (pat : _) _) : rest)
- = case pat of
- ConPat n _ _ | n `eqId` data_con -> (info:rest_yes, rest_no)
- WildPat _ -> (info:rest_yes, info:rest_no)
- -- WildPats will be in the shadows only,
- -- and they go into both groups
- other_pat -> (rest_yes, info:rest_no)
- where
- (rest_yes, rest_no) = splitByCon rest
+ match (ex_dicts ++ arg_vars ++ vars)
+ (map shift_con_pat all_eqns) `thenDs` \ match_result ->
+ -- Substitute over the result
+ let
+ match_result' | null ex_tvs = match_result
+ | otherwise = adjustMatchResult subst_it match_result
+ in
+ returnDs (data_con, ex_tvs ++ ex_dicts ++ arg_vars, match_result')
+ where
shift_con_pat :: EquationInfo -> EquationInfo
- shift_con_pat (EqnInfo (ConPat _ _ pats': pats) match_result)
- = EqnInfo (pats' ++ pats) match_result
- shift_con_pat (EqnInfo (WildPat _: pats) match_result) -- Will only happen in shadow
- = EqnInfo ([WildPat (typeOfPat arg_pat) | arg_pat <- arg_pats] ++ pats) match_result
- shift_con_pat other = panic "matchConFamily:match_cons_used:shift_con_pat"
+ shift_con_pat (EqnInfo n ctx (ConPat _ _ ex_tvs' ex_dicts' arg_pats: pats) match_result)
+ = EqnInfo n ctx (new_pats ++ pats) match_result
+ where
+ new_pats = map VarPat ex_dicts' ++ arg_pats
+
+ -- We 'substitute' by going: (/\ tvs' -> e) tvs
+ subst_it e = foldr subst_one e other_eqns
+ subst_one (EqnInfo _ _ (ConPat _ _ ex_tvs' _ _ : _) _) e = mkTyApps (mkLams ex_tvs' e) ex_tys
+ ex_tys = mkTyVarTys ex_tvs
\end{code}
Note on @shift_con_pats@ just above: does what the list comprehension in
projects / ghc-hetmet.git / blobdiff