%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1995
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[DsListComp]{Desugaring list comprehensions}
\begin{code}
module DsListComp ( dsListComp ) where
+#include "HsVersions.h"
-import AbsSyn -- the stuff being desugared
-import PlainCore -- the output of desugaring;
- -- importing this module also gets all the
- -- CoreSyn utility functions
-import DsMonad -- the monadery used in the desugarer
+import {-# SOURCE #-} DsExpr ( dsExpr, dsLet )
+
+import BasicTypes ( Boxity(..) )
+import HsSyn ( OutPat(..), HsExpr(..), Stmt(..), HsMatchContext(..) )
+import TcHsSyn ( TypecheckedStmt )
+import DsHsSyn ( outPatType )
+import CoreSyn
-import AbsPrel ( mkFunTy, nilDataCon, consDataCon, listTyCon,
- mkBuild, mkFoldr
- )
-import AbsUniType ( alpha_tv, alpha, mkTyVarTy, mkForallTy )
-import CmdLineOpts ( GlobalSwitch(..) )
-import DsExpr ( dsExpr )
+import DsMonad -- the monadery used in the desugarer
import DsUtils
-import Id ( getIdInfo, replaceIdInfo )
-import IdInfo
+
+import CmdLineOpts ( opt_FoldrBuildOn )
+import CoreUtils ( exprType, mkIfThenElse )
+import Id ( idType )
+import Var ( Id )
+import Type ( mkTyVarTy, mkFunTys, mkFunTy, Type )
+import TysPrim ( alphaTyVar )
+import TysWiredIn ( nilDataCon, consDataCon, unitDataConId, tupleCon, mkListTy, mkTupleTy )
import Match ( matchSimply )
-import Util
+import PrelNames ( foldrName, buildName )
+import SrcLoc ( noSrcLoc )
+import List ( zip4 )
\end{code}
List comprehensions may be desugared in one of two ways: ``ordinary''
There will be at least one ``qualifier'' in the input.
\begin{code}
-dsListComp :: PlainCoreExpr -> [TypecheckedQual] -> DsM PlainCoreExpr
+dsListComp :: [TypecheckedStmt]
+ -> Type -- Type of list elements
+ -> DsM CoreExpr
-dsListComp expr quals
- = let expr_ty = typeOfCoreExpr expr
- in
- ifSwitchSetDs FoldrBuildOn (
- new_alpha_tyvar `thenDs` \ (n_tyvar, n_ty) ->
- let
- c_ty = expr_ty `mkFunTy` (n_ty `mkFunTy` n_ty)
- g_ty = mkForallTy [alpha_tv] (
- (expr_ty `mkFunTy` (alpha `mkFunTy` alpha))
- `mkFunTy` (alpha `mkFunTy` alpha))
- in
- newSysLocalsDs [c_ty,n_ty,g_ty] `thenDs` \ [c, n, g] ->
-
- dfListComp expr expr_ty
- c_ty c
- n_ty n
- quals `thenDs` \ result ->
-
- returnDs (mkBuild expr_ty n_tyvar c n g result)
-
- ) {-else be boring-} (
- deListComp expr quals (nIL_EXPR expr_ty)
- )
- where
- nIL_EXPR ty = CoCon nilDataCon [ty] []
+dsListComp quals elt_ty
+ | not opt_FoldrBuildOn -- Be boring
+ = deListComp quals (mkNilExpr elt_ty)
- new_alpha_tyvar :: DsM (TyVar, UniType)
- new_alpha_tyvar
- = newTyVarsDs [alpha_tv] `thenDs` \ [new_ty] ->
- returnDs (new_ty,mkTyVarTy new_ty)
+ | otherwise -- foldr/build lives!
+ = newTyVarsDs [alphaTyVar] `thenDs` \ [n_tyvar] ->
+ let
+ n_ty = mkTyVarTy n_tyvar
+ 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 buildName `thenDs` \ build_id ->
+ returnDs (Var build_id `App` Type elt_ty
+ `App` mkLams [n_tyvar, c, n] result)
\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.
-\begin{code}
-deListComp :: PlainCoreExpr -> [TypecheckedQual] -> PlainCoreExpr -> DsM PlainCoreExpr
+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 | ((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]]
+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.
-deListComp expr [] list -- Figure 7.4, SLPJ, p 135, rule C above
- = mkCoConDs consDataCon [typeOfCoreExpr expr] [expr, list]
-
-deListComp expr ((FilterQual filt): quals) list -- rule B above
- = dsExpr filt `thenDs` \ core_filt ->
- deListComp expr quals list `thenDs` \ core_rest ->
- returnDs ( mkCoreIfThenElse core_filt core_rest list )
+\begin{code}
-deListComp expr ((GeneratorQual pat list1):quals) core_list2 -- rule A' above
- = dsExpr list1 `thenDs` \ core_list1 ->
- let
- u3_ty@u1_ty = typeOfCoreExpr core_list1 -- two names, same thing
+deListComp :: [TypecheckedStmt] -> CoreExpr -> DsM CoreExpr
- -- u1_ty is a [alpha] type, and u2_ty = alpha
- u2_ty = typeOfPat pat
-
- res_ty = typeOfCoreExpr core_list2
- h_ty = mkFunTy u1_ty res_ty
+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
- newSysLocalsDs [h_ty, u1_ty, u2_ty, u3_ty]
- `thenDs` \ [h', u1, u2, u3] ->
- {-
- Make the function h unfoldable by the deforester.
- Since it only occurs once in the body, we can't get
- an increase in code size by unfolding it.
- -}
--- getSwitchCheckerDs `thenDs` \ sw_chkr ->
- let
- h = if False -- LATER: sw_chkr DoDeforest???
- then replaceIdInfo h' (addInfo (getIdInfo h') DoDeforest)
- else h'
+ 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
- -- the "fail" value ...
- mkCoAppDs (CoVar h) (CoVar u3) `thenDs` \ core_fail ->
+ 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
+
+ -- Last: the one to return
+deListComp [ExprStmt 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)
+
+ -- Non-last: must be a guard
+deListComp (ExprStmt guard locn : quals) list -- rule B above
+ = dsExpr guard `thenDs` \ core_guard ->
+ deListComp quals list `thenDs` \ core_rest ->
+ returnDs (mkIfThenElse core_guard core_rest list)
+
+-- [e | let B, qs] = let B in [e | qs]
+deListComp (LetStmt binds : quals) list
+ = deListComp quals list `thenDs` \ core_rest ->
+ dsLet binds core_rest
+
+deListComp (BindStmt pat list1 locn : quals) core_list2 -- rule A' above
+ = dsExpr list1 `thenDs` \ core_list1 ->
+ deBindComp pat core_list1 quals core_list2
- deListComp expr quals core_fail `thenDs` \ rest_expr ->
+deBindComp pat core_list1 quals core_list2
+ = let
+ u3_ty@u1_ty = exprType core_list1 -- two names, same thing
- matchSimply (CoVar u2) pat res_ty rest_expr core_fail `thenDs` \ core_match ->
+ -- u1_ty is a [alpha] type, and u2_ty = alpha
+ u2_ty = outPatType pat
- mkCoAppDs (CoVar h) core_list1 `thenDs` \ letrec_body ->
+ res_ty = exprType core_list2
+ h_ty = u1_ty `mkFunTy` res_ty
+ in
+ newSysLocalsDs [h_ty, u1_ty, u2_ty, u3_ty] `thenDs` \ [h, u1, u2, u3] ->
- returnDs (
- mkCoLetrecAny [
- ( h,
- (CoLam [ u1 ]
- (CoCase (CoVar u1)
- (CoAlgAlts
- [(nilDataCon, [], core_list2),
- (consDataCon, [u2, u3], core_match)]
- CoNoDefault)))
- )] letrec_body
- )
+ -- the "fail" value ...
+ let
+ core_fail = App (Var h) (Var u3)
+ letrec_body = App (Var h) core_list1
+ in
+ deListComp quals core_fail `thenDs` \ rest_expr ->
+ matchSimply (Var u2) ListComp pat
+ rest_expr core_fail `thenDs` \ core_match ->
+ let
+ rhs = Lam u1 $
+ Case (Var u1) u1 [(DataAlt nilDataCon, [], core_list2),
+ (DataAlt consDataCon, [u2, u3], core_match)]
+ in
+ returnDs (Let (Rec [(h, rhs)]) letrec_body)
\end{code}
+
%************************************************************************
%* *
\subsection[DsListComp-foldr-build]{Foldr/Build desugaring of list comprehensions}
%************************************************************************
@dfListComp@ are the rules used with foldr/build turned on:
+
\begin{verbatim}
-TE < [ e | ] >> c n = c e n
-TE << [ e | b , q ] >> c n = if b then TE << [ e | q ] >> c n else n
-TE << [ e | p <- l , q ] c n = foldr
- (\ TE << p >> b -> TE << [ e | q ] >> c b
- _ b -> b) n l
+TE[ e | ] c n = c e n
+TE[ e | b , q ] c n = if b then TE[ e | q ] c n else n
+TE[ e | p <- l , q ] c n = let
+ f = \ x b -> case x of
+ p -> TE[ e | q ] c b
+ _ -> b
+ in
+ foldr f n l
\end{verbatim}
+
\begin{code}
-dfListComp :: PlainCoreExpr -- the inside of the comp
- -> UniType -- the type of the inside
- -> UniType -> Id -- 'c'; its type and id
- -> UniType -> Id -- 'n'; its type and id
- -> [TypecheckedQual] -- the rest of the qual's
- -> DsM PlainCoreExpr
-
-dfListComp expr expr_ty c_ty c_id n_ty n_id []
- = mkCoAppDs (CoVar c_id) expr `thenDs` \ inner ->
- mkCoAppDs inner (CoVar n_id)
-
-dfListComp expr expr_ty c_ty c_id n_ty n_id ((FilterQual filt) : quals)
- = dsExpr filt `thenDs` \ core_filt ->
- dfListComp expr expr_ty c_ty c_id n_ty n_id quals
- `thenDs` \ core_rest ->
- returnDs (mkCoreIfThenElse core_filt core_rest (CoVar n_id))
-
-dfListComp expr expr_ty c_ty c_id n_ty n_id ((GeneratorQual pat list1):quals)
+dfListComp :: Id -> Id -- 'c' and 'n'
+ -> [TypecheckedStmt] -- the rest of the qual's
+ -> DsM CoreExpr
+
+ -- Last: the one to return
+dfListComp c_id n_id [ExprStmt expr locn]
+ = dsExpr expr `thenDs` \ core_expr ->
+ returnDs (mkApps (Var c_id) [core_expr, Var n_id])
+
+ -- Non-last: must be a guard
+dfListComp c_id n_id (ExprStmt guard 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 n_id (LetStmt binds : quals)
+ -- new in 1.3, local bindings
+ = dfListComp c_id n_id quals `thenDs` \ core_rest ->
+ dsLet binds core_rest
+
+dfListComp c_id n_id (BindStmt pat list1 locn : quals)
-- evaluate the two lists
= dsExpr list1 `thenDs` \ core_list1 ->
-- find the required type
-
- let p_ty = typeOfPat pat
- b_ty = n_ty -- alias b_ty to n_ty
- fn_ty = p_ty `mkFunTy` (b_ty `mkFunTy` b_ty)
- lst_ty = typeOfCoreExpr core_list1
+ let x_ty = outPatType pat
+ b_ty = idType n_id
in
-- create some new local id's
-
- newSysLocalsDs [b_ty,p_ty,fn_ty,lst_ty] `thenDs` \ [b,p,fn,lst] ->
+ newSysLocalsDs [b_ty,x_ty] `thenDs` \ [b,x] ->
-- build rest of the comprehesion
+ dfListComp c_id b quals `thenDs` \ core_rest ->
- dfListComp expr expr_ty c_ty c_id b_ty b quals `thenDs` \ core_rest ->
-- build the pattern match
-
- matchSimply (CoVar p) pat b_ty core_rest (CoVar b) `thenDs` \ core_expr ->
+ matchSimply (Var x) ListComp pat core_rest (Var b) `thenDs` \ core_expr ->
-- now build the outermost foldr, and return
-
+ dsLookupGlobalValue foldrName `thenDs` \ foldr_id ->
returnDs (
- mkCoLetsAny
- [CoNonRec fn (CoLam [p,b] core_expr),
- CoNonRec lst core_list1]
- (mkFoldr p_ty n_ty fn n_id lst)
+ Var foldr_id `App` Type x_ty
+ `App` Type b_ty
+ `App` mkLams [x, b] core_expr
+ `App` Var n_id
+ `App` core_list1
)
\end{code}
+
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