import {-# SOURCE #-} DsExpr ( dsExpr, dsLet )
-import HsSyn ( Stmt(..) )
-import TcHsSyn ( TypecheckedStmt )
-import DsHsSyn ( outPatType )
+import BasicTypes ( Boxity(..) )
+import HsSyn ( OutPat(..), HsExpr(..), Stmt(..), HsMatchContext(..), HsDoContext(..) )
+import TcHsSyn ( TypecheckedStmt, TypecheckedPat, TypecheckedHsExpr, outPatType )
import CoreSyn
import DsMonad -- the monadery used in the desugarer
import Var ( Id )
import Type ( mkTyVarTy, mkFunTys, mkFunTy, Type )
import TysPrim ( alphaTyVar )
-import TysWiredIn ( nilDataCon, consDataCon )
+import TysWiredIn ( nilDataCon, consDataCon, unitDataConId, mkListTy, mkTupleTy )
import Match ( matchSimply )
-import PrelNames ( foldrIdKey, buildIdKey )
+import PrelNames ( foldrName, buildName )
+import SrcLoc ( noSrcLoc )
\end{code}
List comprehensions may be desugared in one of two ways: ``ordinary''
-> DsM CoreExpr
dsListComp quals elt_ty
- | not opt_FoldrBuildOn -- Be boring
+ | not opt_FoldrBuildOn -- Be boring
+ || isParallelComp quals
= deListComp quals (mkNilExpr elt_ty)
| otherwise -- foldr/build lives!
c_ty = mkFunTys [elt_ty, n_ty] n_ty
in
newSysLocalsDs [c_ty,n_ty] `thenDs` \ [c, n] ->
-
dfListComp c n quals `thenDs` \ result ->
-
- dsLookupGlobalValue buildIdKey `thenDs` \ build_id ->
+ dsLookupGlobalValue buildName `thenDs` \ build_id ->
returnDs (Var build_id `App` Type elt_ty
`App` mkLams [n_tyvar, c, n] result)
+
+ where isParallelComp (ParStmtOut bndrstmtss : _) = True
+ isParallelComp _ = False
\end{code}
%************************************************************************
is the TE translation scheme. Note that we carry around the @L@ list
already desugared. @dsListComp@ does the top TE rule mentioned above.
+To the above, we add an additional rule to deal with parallel list
+comprehensions. The translation goes roughly as follows:
+ [ e | p1 <- e11, let v1 = e12, p2 <- e13
+ | 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
+the comprehensions, and then we hand things off the the desugarer for bindings.
+The zip function is generated here a) because it's small, and b) because then we
+don't have to deal with arbitrary limits on the number of zip functions in the
+prelude, nor which library the zip function came from.
+The introduced tuples are Boxed, but only because I couldn't get it to work
+with the Unboxed variety.
\begin{code}
+
deListComp :: [TypecheckedStmt] -> CoreExpr -> DsM CoreExpr
-deListComp [ReturnStmt expr] list -- Figure 7.4, SLPJ, p 135, rule C above
+deListComp (ParStmtOut bndrstmtss : quals) list
+ = 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 [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 (GuardStmt guard locn : quals) list -- rule B above
+ -- Non-last: must be a guard
+deListComp (ExprStmt guard ty locn : quals) list -- rule B above
= dsExpr guard `thenDs` \ core_guard ->
deListComp quals list `thenDs` \ core_rest ->
returnDs (mkIfThenElse core_guard core_rest list)
deListComp (BindStmt pat list1 locn : quals) core_list2 -- rule A' above
= dsExpr list1 `thenDs` \ core_list1 ->
- let
+ 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
-- u1_ty is a [alpha] type, and u2_ty = alpha
letrec_body = App (Var h) core_list1
in
deListComp quals core_fail `thenDs` \ rest_expr ->
- matchSimply (Var u2) ListCompMatch pat
+ matchSimply (Var u2) (DoCtxt ListComp) pat
rest_expr core_fail `thenDs` \ core_match ->
let
rhs = Lam u1 $
\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}
-> [TypecheckedStmt] -- the rest of the qual's
-> DsM CoreExpr
-dfListComp c_id n_id [ReturnStmt expr]
+ -- Last: the one to return
+dfListComp c_id n_id [ResultStmt expr locn]
= dsExpr expr `thenDs` \ core_expr ->
returnDs (mkApps (Var c_id) [core_expr, Var n_id])
-dfListComp c_id n_id (GuardStmt guard locn : quals)
+ -- Non-last: must be a guard
+dfListComp c_id n_id (ExprStmt guard ty locn : quals)
= dsExpr guard `thenDs` \ core_guard ->
dfListComp c_id n_id quals `thenDs` \ core_rest ->
returnDs (mkIfThenElse core_guard core_rest (Var n_id))
dfListComp c_id b quals `thenDs` \ core_rest ->
-- build the pattern match
- matchSimply (Var x) ListCompMatch pat core_rest (Var b) `thenDs` \ core_expr ->
+ matchSimply (Var x) (DoCtxt ListComp)
+ pat core_rest (Var b) `thenDs` \ core_expr ->
-- now build the outermost foldr, and return
- dsLookupGlobalValue foldrIdKey `thenDs` \ foldr_id ->
+ dsLookupGlobalValue foldrName `thenDs` \ foldr_id ->
returnDs (
Var foldr_id `App` Type x_ty
`App` Type b_ty
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