import BasicTypes ( Boxity(..) )
import HsSyn ( OutPat(..), HsExpr(..), Stmt(..), HsMatchContext(..) )
-import TcHsSyn ( TypecheckedStmt )
+import TcHsSyn ( TypecheckedStmt, TypecheckedPat, TypecheckedHsExpr )
import DsHsSyn ( outPatType )
import CoreSyn
import Var ( Id )
import Type ( mkTyVarTy, mkFunTys, mkFunTy, Type )
import TysPrim ( alphaTyVar )
-import TysWiredIn ( nilDataCon, consDataCon, unitDataConId, tupleCon, mkListTy, mkTupleTy )
+import TysWiredIn ( nilDataCon, consDataCon, unitDataConId, mkListTy, mkTupleTy )
import Match ( matchSimply )
import PrelNames ( foldrName, buildName )
import SrcLoc ( noSrcLoc )
-import List ( zip4 )
\end{code}
List comprehensions may be desugared in one of two ways: ``ordinary''
[ e | p1 <- e11, let v1 = e12, p2 <- e13
| q1 <- e21, let v2 = e22, q2 <- e23]
=>
- [ e | ((p1,v1,p2), (q1,v2,q2)) <-
- zip [(p1,v1,p2) | p1 <- e11, let v1 = e12, p2 <- e13]
- [(q1,v2,q2) | q1 <- e21, let v2 = e22, q2 <- e23]]
+ [ e | ((x1, .., xn), (y1, ..., ym)) <-
+ zip [(x1,..,xn) | p1 <- e11, let v1 = e12, p2 <- e13]
+ [(y1,..,ym) | q1 <- e21, let v2 = e22, q2 <- e23]]
+where (x1, .., xn) are the variables bound in p1, v1, p2
+ (y1, .., ym) are the variables bound in q1, v2, q2
+
In the translation below, the ParStmtOut branch translates each parallel branch
into a sub-comprehension, and desugars each independently. The resulting lists
are fed to a zip function, we create a binding for all the variables bound in all
deListComp :: [TypecheckedStmt] -> CoreExpr -> DsM CoreExpr
deListComp (ParStmtOut bndrstmtss : quals) list
- = mapDs doListComp qualss `thenDs` \ exps ->
- mapDs genAS bndrss `thenDs` \ ass ->
- mapDs genA bndrss `thenDs` \ as ->
- mapDs genAS' bndrss `thenDs` \ as's ->
- let retTy = myTupleTy Boxed (length bndrss) qualTys
- zipTy = foldr mkFunTy (mkListTy retTy) (map mkListTy qualTys)
- in
- newSysLocalDs zipTy `thenDs` \ zipFn ->
- let target = mkConsExpr retTy (mkTupleExpr as) (foldl App (Var zipFn) (map Var as's))
- zipExp = mkLet zipFn (zip4 bndrss ass as as's) exps target
- in
- deBindComp pat zipExp quals list
- where (bndrss, stmtss) = unzip bndrstmtss
- pats = map (\ps -> mkTuplePat (map VarPat ps)) bndrss
- mkTuplePat [p] = p
- mkTuplePat ps = TuplePat ps Boxed
- pat = TuplePat pats Boxed
-
- qualss = map mkQuals bndrstmtss
- mkQuals (bndrs, stmts) = (bndrs, stmts ++ [ExprStmt (myTupleExpr bndrs) noSrcLoc])
-
- qualTys = map mkBndrsTy bndrss
- mkBndrsTy bndrs = myTupleTy Boxed (length bndrs) (map idType bndrs)
-
- doListComp (bndrs, stmts)
- = dsListComp stmts (mkBndrsTy bndrs)
- genA bndrs = newSysLocalDs (mkBndrsTy bndrs)
- genAS bndrs = newSysLocalDs (mkListTy (mkBndrsTy bndrs))
- genAS' bndrs = newSysLocalDs (mkListTy (mkBndrsTy bndrs))
-
- mkLet zipFn vars exps target
- = Let (Rec [(zipFn,
- foldr Lam (mkBody target vars) (map getAs vars))])
- (foldl App (Var zipFn) exps)
- getAs (_, as, _, _) = as
- mkBody target vars
- = foldr mkCase (foldr mkTuplCase target vars) vars
- mkCase (ps, as, a, as') rest
- = Case (Var as) as [(DataAlt nilDataCon, [], mkConApp nilDataCon []),
- (DataAlt consDataCon, [a, as'], rest)]
- mkTuplCase ([p], as, a, as') rest
- = App (Lam p rest) (Var a)
- mkTuplCase (ps, as, a, as') rest
- = Case (Var a) a [(DataAlt (tupleCon Boxed (length ps)), ps, rest)]
-
- myTupleTy boxity arity [ty] = ty
- myTupleTy boxity arity tys = mkTupleTy boxity arity tys
- myTupleExpr [] = HsVar unitDataConId
- myTupleExpr [id] = HsVar id
- myTupleExpr ids = ExplicitTuple [ HsVar i | i <- ids ] Boxed
+ = mapDs do_list_comp bndrstmtss `thenDs` \ exps ->
+ mkZipBind qual_tys `thenDs` \ (zip_fn, zip_rhs) ->
+
+ -- Deal with [e | pat <- zip l1 .. ln] in example above
+ deBindComp pat (Let (Rec [(zip_fn, zip_rhs)]) (mkApps (Var zip_fn) exps))
+ quals list
+
+ where -- pat is the pattern ((x1,..,xn), (y1,..,ym)) in the example above
+ pat = TuplePat pats Boxed
+ pats = map (\(bs,_) -> mk_hs_tuple_pat bs) bndrstmtss
+
+ -- Types of (x1,..,xn), (y1,..,yn) etc
+ qual_tys = [ mk_bndrs_tys bndrs | (bndrs,_) <- bndrstmtss ]
+
+ do_list_comp (bndrs, stmts)
+ = dsListComp (stmts ++ [ResultStmt (mk_hs_tuple_expr bndrs) noSrcLoc])
+ (mk_bndrs_tys bndrs)
+
+ mk_bndrs_tys bndrs = mk_tuple_ty (map idType bndrs)
-- Last: the one to return
-deListComp [ExprStmt expr locn] list -- Figure 7.4, SLPJ, p 135, rule C above
+deListComp [ResultStmt expr locn] list -- Figure 7.4, SLPJ, p 135, rule C above
= dsExpr expr `thenDs` \ core_expr ->
returnDs (mkConsExpr (exprType core_expr) core_expr list)
deListComp (BindStmt pat list1 locn : quals) core_list2 -- rule A' above
= dsExpr list1 `thenDs` \ core_list1 ->
deBindComp pat core_list1 quals core_list2
+\end{code}
+
+\begin{code}
deBindComp pat core_list1 quals core_list2
= let
u3_ty@u1_ty = exprType core_list1 -- two names, same thing
\end{code}
+\begin{code}
+mkZipBind :: [Type] -> DsM (Id, CoreExpr)
+-- mkZipBind [t1, t2]
+-- = (zip, \as1:[t1] as2:[t2]
+-- -> case as1 of
+-- [] -> []
+-- (a1:as'1) -> case as2 of
+-- [] -> []
+-- (a2:as'2) -> (a2,a2) : zip as'1 as'2)]
+
+mkZipBind elt_tys
+ = mapDs newSysLocalDs list_tys `thenDs` \ ass ->
+ mapDs newSysLocalDs elt_tys `thenDs` \ as' ->
+ mapDs newSysLocalDs list_tys `thenDs` \ as's ->
+ newSysLocalDs zip_fn_ty `thenDs` \ zip_fn ->
+ let
+ inner_rhs = mkConsExpr ret_elt_ty (mkTupleExpr as') (mkVarApps (Var zip_fn) as's)
+ zip_body = foldr mk_case inner_rhs (zip3 ass as' as's)
+ in
+ returnDs (zip_fn, mkLams ass zip_body)
+ where
+ list_tys = map mkListTy elt_tys
+ ret_elt_ty = mk_tuple_ty elt_tys
+ zip_fn_ty = mkFunTys list_tys (mkListTy ret_elt_ty)
+
+ mk_case (as, a', as') rest
+ = Case (Var as) as [(DataAlt nilDataCon, [], mkNilExpr ret_elt_ty),
+ (DataAlt consDataCon, [a', as'], rest)]
+
+-- Helper function
+mk_tuple_ty :: [Type] -> Type
+mk_tuple_ty [ty] = ty
+mk_tuple_ty tys = mkTupleTy Boxed (length tys) tys
+
+-- Helper functions that makes an HsTuple only for non-1-sized tuples
+mk_hs_tuple_expr :: [Id] -> TypecheckedHsExpr
+mk_hs_tuple_expr [] = HsVar unitDataConId
+mk_hs_tuple_expr [id] = HsVar id
+mk_hs_tuple_expr ids = ExplicitTuple [ HsVar i | i <- ids ] Boxed
+
+mk_hs_tuple_pat :: [Id] -> TypecheckedPat
+mk_hs_tuple_pat [b] = VarPat b
+mk_hs_tuple_pat bs = TuplePat (map VarPat bs) Boxed
+\end{code}
+
+
%************************************************************************
%* *
\subsection[DsListComp-foldr-build]{Foldr/Build desugaring of list comprehensions}
-> DsM CoreExpr
-- Last: the one to return
-dfListComp c_id n_id [ExprStmt expr locn]
+dfListComp c_id n_id [ResultStmt expr locn]
= dsExpr expr `thenDs` \ core_expr ->
returnDs (mkApps (Var c_id) [core_expr, Var n_id])
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