%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[MatchCon]{Pattern-matching constructors}
\begin{code}
-#include "HsVersions.h"
-
module MatchCon ( matchConFamily ) where
-import Ubiq
-import DsLoop ( match ) -- break match-ish loop
+#include "HsVersions.h"
+
+import {-# SOURCE #-} Match ( match )
-import HsSyn ( OutPat(..), HsLit, HsExpr )
-import DsHsSyn ( outPatType )
+import HsSyn ( OutPat(..) )
import DsMonad
import DsUtils
-import Id ( isDataCon, GenId{-instances-} )
-import Util ( panic, assertPanic )
+import Id ( Id )
+import CoreSyn
+import Type ( mkTyVarTys )
+import Unique ( Uniquable(..), Unique )
+import UniqFM -- Until equivClassesUniq moves to Util
+import Outputable
\end{code}
We are confronted with the first column of patterns in a set of
\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
+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 ->
+
+ returnDs (mkCoAlgCaseMatchResult var alts)
\end{code}
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 []
-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 ->
-
- -- 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 == 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 (outPatType 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
+
+
+-- Belongs in Util.lhs
+equivClassesByUniq :: (a -> Unique) -> [a] -> [[a]]
+ -- NB: it's *very* important that if we have the input list [a,b,c],
+ -- where a,b,c all have the same unique, then we get back the list
+ -- [a,b,c]
+ -- not
+ -- [c,b,a]
+ -- Hence the use of foldr, plus the reversed-args tack_on below
+equivClassesByUniq get_uniq xs
+ = eltsUFM (foldr add emptyUFM xs)
+ where
+ add a ufm = addToUFM_C tack_on ufm (get_uniq a) [a]
+ tack_on old new = new++old
\end{code}
Note on @shift_con_pats@ just above: does what the list comprehension in
projects / ghc-hetmet.git / blobdiff