#include "HsVersions.h"
+import Id( idType )
+
import {-# SOURCE #-} Match ( match )
import HsSyn ( Pat(..), HsConDetails(..) )
-
+import DsBinds ( dsLHsBinds )
+import DataCon ( isVanillaDataCon, dataConInstOrigArgTys )
+import TcType ( tcTyConAppArgs )
+import Type ( mkTyVarTys )
+import CoreSyn
import DsMonad
import DsUtils
import Id ( Id )
-import Subst ( mkSubst, mkInScopeSet, bindSubst, substExpr )
-import CoreFVs ( exprFreeVars )
-import VarEnv ( emptySubstEnv )
+import Type ( Type )
import ListSetOps ( equivClassesByUniq )
-import SrcLoc ( unLoc )
+import SrcLoc ( unLoc, Located(..) )
import Unique ( Uniquable(..) )
+import Outputable
\end{code}
We are confronted with the first column of patterns in a set of
@match_cons_used@ does all the real work.
\begin{code}
matchConFamily :: [Id]
+ -> Type
-> [EquationInfo]
-> DsM MatchResult
-
-matchConFamily (var:vars) eqns_info
+matchConFamily (var:vars) ty 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 _ _ (ConPatOut data_con _ _ _ _ : _) _) = getUnique data_con
+ groups = equivClassesByUniq get_uniq eqns_info
+ get_uniq (EqnInfo { eqn_pats = ConPatOut (L _ data_con) _ _ _ _ _ : _}) = getUnique data_con
+
+ -- Get the wrapper from the head of each group. We're going to
+ -- use it as the pattern in this case expression, so we need to
+ -- ensure that any type variables it mentions in the pattern are
+ -- in scope. So we put its wrappers outside the case, and
+ -- zap the wrapper for it.
+ wraps :: [CoreExpr -> CoreExpr]
+ wraps = map (eqn_wrap . head) groups
+
+ groups' = [ eqn { eqn_wrap = idWrapper } : eqns | eqn:eqns <- groups ]
in
-- Now make a case alternative out of each group
- mappM (match_con vars) eqn_groups `thenDs` \ alts ->
-
- returnDs (mkCoAlgCaseMatchResult var alts)
+ mappM (match_con vars ty) groups' `thenDs` \ alts ->
+ returnDs (adjustMatchResult (foldr (.) idWrapper wraps) $
+ mkCoAlgCaseMatchResult var ty 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.
+Wadler's chapter in SLPJ. The function @shift_con_pats@ does what the
+list comprehension in @matchClause@ (SLPJ, p.~94) does, except things
+are trickier in real life. Works for @ConPats@, and we want it to
+fail catastrophically for anything else (which a list comprehension
+wouldn't). Cf.~@shift_lit_pats@ in @MatchLits@.
\begin{code}
-match_con vars (eqn1@(EqnInfo _ _ (ConPatOut data_con (PrefixCon arg_pats) _ ex_tvs ex_dicts : _) _)
- : other_eqns)
- = -- Make new vars for the con arguments; avoid new locals where possible
- mappM selectMatchVarL arg_pats `thenDs` \ arg_vars ->
-
- -- Now do the business to make the alt for _this_ ConPat ...
- match (arg_vars ++ vars)
- (map shift_con_pat (eqn1:other_eqns)) `thenDs` \ match_result ->
-
- -- [See "notes on do_subst" below this function]
- -- Make the ex_tvs and ex_dicts line up with those
- -- in the first pattern. Remember, they are all guaranteed to be variables
- let
- match_result' | null ex_tvs = match_result
- | null other_eqns = match_result
- | otherwise = adjustMatchResult do_subst match_result
- in
-
- returnDs (data_con, ex_tvs ++ ex_dicts ++ arg_vars, match_result')
+match_con vars ty eqns
+ = do { -- Make new vars for the con arguments; avoid new locals where possible
+ arg_vars <- selectMatchVars (map unLoc arg_pats1) arg_tys
+ ; eqns' <- mapM shift eqns
+ ; match_result <- match (arg_vars ++ vars) ty eqns'
+ ; return (con, tvs1 ++ dicts1 ++ arg_vars, match_result) }
where
- shift_con_pat :: EquationInfo -> EquationInfo
- shift_con_pat (EqnInfo n ctx (ConPatOut _ (PrefixCon arg_pats) _ _ _ : pats) match_result)
- = EqnInfo n ctx (map unLoc arg_pats ++ pats) match_result
-
- other_pats = [p | EqnInfo _ _ (p:_) _ <- other_eqns]
-
- var_prs = concat [ (ex_tvs' `zip` ex_tvs) ++
- (ex_dicts' `zip` ex_dicts)
- | ConPatOut _ _ _ ex_tvs' ex_dicts' <- other_pats ]
-
- do_subst e = substExpr subst e
- where
- subst = foldl (\ s (v', v) -> bindSubst s v' v) in_scope var_prs
- in_scope = mkSubst (mkInScopeSet (exprFreeVars e)) emptySubstEnv
- -- We put all the free variables of e into the in-scope
- -- set of the substitution, not because it is necessary,
- -- but to suppress the warning in Subst.lookupInScope
- -- Tiresome, but doing the substitution at all is rare.
+ ConPatOut (L _ con) tvs1 dicts1 _ (PrefixCon arg_pats1) pat_ty = firstPat (head eqns)
+
+ shift eqn@(EqnInfo { eqn_wrap = wrap,
+ eqn_pats = ConPatOut _ tvs ds bind (PrefixCon arg_pats) _ : pats })
+ = do { prs <- dsLHsBinds bind
+ ; return (eqn { eqn_wrap = wrap . wrapBinds (tvs `zip` tvs1)
+ . wrapBinds (ds `zip` dicts1)
+ . mkDsLet (Rec prs),
+ eqn_pats = map unLoc arg_pats ++ pats }) }
+
+ -- Get the arg types, which we use to type the new vars
+ -- to match on, from the "outside"; the types of pats1 may
+ -- be more refined, and hence won't do
+ arg_tys = dataConInstOrigArgTys con inst_tys
+ inst_tys | isVanillaDataCon con = tcTyConAppArgs pat_ty -- Newtypes opaque!
+ | otherwise = mkTyVarTys tvs1
\end{code}
-Note on @shift_con_pats@ just above: does what the list comprehension in
-@matchClause@ (SLPJ, p.~94) does, except things are trickier in real
-life. Works for @ConPats@, and we want it to fail catastrophically
-for anything else (which a list comprehension wouldn't).
-Cf.~@shift_lit_pats@ in @MatchLits@.
-
-
-Notes on do_subst stuff
-~~~~~~~~~~~~~~~~~~~~~~~
+Note [Existentials in shift_con_pat]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
data T = forall a. Ord a => T a (a->Int)
When we put in the tyvars etc we get
f (T a (d::Ord a) (x::a) (f::a->Int)) True = ...expr1...
- f (T b (e::Ord a) (y::a) (g::a->Int)) True = ...expr2...
+ f (T b (e::Ord b) (y::a) (g::a->Int)) True = ...expr2...
After desugaring etc we'll get a single case:
False -> ...expr2...
*** We have to substitute [a/b, d/e] in expr2! **
-That is what do_subst is doing.
+Hence
+ False -> ....((/\b\(e:Ord b).expr2) a d)....
Originally I tried to use
(\b -> let e = d in expr2) a
to do this substitution. While this is "correct" in a way, it fails
Lint, because e::Ord b but d::Ord a.
-So now I simply do the substitution properly using substExpr.
-
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