import {-# SOURCE #-} Match ( match )
-import HsSyn ( OutPat(..) )
+import HsSyn ( Pat(..), HsConDetails(..) )
import DsMonad
import DsUtils
import Id ( Id )
-import CoreSyn
-import Type ( mkTyVarTys )
+import Subst ( mkSubst, mkInScopeSet, bindSubst, substExpr )
+import CoreFVs ( exprFreeVars )
+import VarEnv ( emptySubstEnv )
import ListSetOps ( equivClassesByUniq )
+import SrcLoc ( unLoc )
import Unique ( Uniquable(..) )
\end{code}
-- 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
+ get_uniq (EqnInfo _ _ (ConPatOut data_con _ _ _ _ : _) _) = getUnique data_con
in
-- Now make a case alternative out of each group
- mapDs (match_con vars) eqn_groups `thenDs` \ alts ->
+ mappM (match_con vars) eqn_groups `thenDs` \ alts ->
returnDs (mkCoAlgCaseMatchResult var alts)
\end{code}
Wadler's chapter in SLPJ.
\begin{code}
-match_con vars all_eqns@(EqnInfo n ctx (ConPat data_con _ ex_tvs ex_dicts arg_pats : pats1) match_result1 : other_eqns)
+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
- mapDs selectMatchVar arg_pats `thenDs` \ arg_vars ->
+ mappM selectMatchVarL arg_pats `thenDs` \ arg_vars ->
-- Now do the business to make the alt for _this_ ConPat ...
- match (ex_dicts ++ arg_vars ++ vars)
- (map shift_con_pat all_eqns) `thenDs` \ match_result ->
+ match (arg_vars ++ vars)
+ (map shift_con_pat (eqn1:other_eqns)) `thenDs` \ match_result ->
- -- Substitute over the 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
- | otherwise = adjustMatchResult subst_it match_result
- in
+ 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')
where
shift_con_pat :: EquationInfo -> EquationInfo
- 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
+ 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.
\end{code}
Note on @shift_con_pats@ just above: does what the list comprehension in
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
+~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+ data T = forall a. Ord a => T a (a->Int)
+
+ f (T x f) True = ...expr1...
+ f (T y g) False = ...expr2..
+
+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...
+
+After desugaring etc we'll get a single case:
+
+ f = \t::T b::Bool ->
+ case t of
+ T a (d::Ord a) (x::a) (f::a->Int)) ->
+ case b of
+ True -> ...expr1...
+ False -> ...expr2...
+
+*** We have to substitute [a/b, d/e] in expr2! **
+That is what do_subst is doing.
+
+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.
+