Desugaring list comprehensions and array comprehensions
\begin{code}
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+-- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
+-- for details
+
module DsListComp ( dsListComp, dsPArrComp ) where
#include "HsVersions.h"
import DsUtils
import DynFlags
-import StaticFlags
import CoreUtils
import Var
import Type
import PrelInfo
import SrcLoc
import Panic
+import Outputable
+
+import Control.Monad ( liftM2 )
\end{code}
List comprehensions may be desugared in one of two ways: ``ordinary''
-> LHsExpr Id
-> Type -- Type of list elements
-> DsM CoreExpr
-dsListComp lquals body elt_ty
- = getDOptsDs `thenDs` \dflags ->
- let
- quals = map unLoc lquals
- in
- if opt_RulesOff || dopt Opt_IgnoreInterfacePragmas dflags
- -- Either rules are switched off, or we are ignoring what there are;
- -- Either way foldr/build won't happen, so use the more efficient
- -- Wadler-style desugaring
- || isParallelComp quals
- -- Foldr-style desugaring can't handle
- -- parallel list comprehensions
- then deListComp quals body (mkNilExpr elt_ty)
-
- else -- Foldr/build should be enabled, so desugar
- -- into foldrs and builds
- 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 body `thenDs` \ result ->
- dsLookupGlobalId buildName `thenDs` \ build_id ->
- returnDs (Var build_id `App` Type elt_ty
- `App` mkLams [n_tyvar, c, n] result)
-
- where isParallelComp (ParStmt bndrstmtss : _) = True
- isParallelComp _ = False
+dsListComp lquals body elt_ty = do
+ dflags <- getDOptsDs
+ let quals = map unLoc lquals
+
+ if not (dopt Opt_RewriteRules dflags) || dopt Opt_IgnoreInterfacePragmas dflags
+ -- Either rules are switched off, or we are ignoring what there are;
+ -- Either way foldr/build won't happen, so use the more efficient
+ -- Wadler-style desugaring
+ || isParallelComp quals
+ -- Foldr-style desugaring can't handle parallel list comprehensions
+ then deListComp quals body (mkNilExpr elt_ty)
+ else do -- Foldr/build should be enabled, so desugar
+ -- into foldrs and builds
+ [n_tyvar] <- newTyVarsDs [alphaTyVar]
+
+ let n_ty = mkTyVarTy n_tyvar
+ c_ty = mkFunTys [elt_ty, n_ty] n_ty
+ [c, n] <- newSysLocalsDs [c_ty, n_ty]
+
+ result <- dfListComp c n quals body
+ build_id <- dsLookupGlobalId buildName
+ returnDs (Var build_id `App` Type elt_ty `App` mkLams [n_tyvar, c, n] result)
+
+ where
+ -- We must test for ParStmt anywhere, not just at the head, because an extension
+ -- to list comprehensions would be to add brackets to specify the associativity
+ -- of qualifier lists. This is really easy to do by adding extra ParStmts into the
+ -- mix of possibly a single element in length, so we do this to leave the possibility open
+ isParallelComp = any isParallelStmt
+
+ isParallelStmt (ParStmt _) = True
+ isParallelStmt _ = False
+
+
+-- This function lets you desugar a inner list comprehension and a list of the binders
+-- of that comprehension that we need in the outer comprehension into such an expression
+-- and the type of the elements that it outputs (tuples of binders)
+dsInnerListComp :: ([LStmt Id], [Id]) -> DsM (CoreExpr, Type)
+dsInnerListComp (stmts, bndrs) = do
+ expr <- dsListComp stmts (mkBigLHsVarTup bndrs) bndrs_tuple_type
+ return (expr, bndrs_tuple_type)
+ where
+ bndrs_types = map idType bndrs
+ bndrs_tuple_type = mkBigCoreTupTy bndrs_types
+
+
+-- This function factors out commonality between the desugaring strategies for TransformStmt.
+-- Given such a statement it gives you back an expression representing how to compute the transformed
+-- list and the tuple that you need to bind from that list in order to proceed with your desugaring
+dsTransformStmt :: Stmt Id -> DsM (CoreExpr, LPat Id)
+dsTransformStmt (TransformStmt (stmts, binders) usingExpr maybeByExpr) = do
+ (expr, binders_tuple_type) <- dsInnerListComp (stmts, binders)
+ usingExpr' <- dsLExpr usingExpr
+
+ using_args <-
+ case maybeByExpr of
+ Nothing -> return [expr]
+ Just byExpr -> do
+ byExpr' <- dsLExpr byExpr
+
+ us <- newUniqueSupply
+ [tuple_binder] <- newSysLocalsDs [binders_tuple_type]
+ let byExprWrapper = mkTupleCase us binders byExpr' tuple_binder (Var tuple_binder)
+
+ return [Lam tuple_binder byExprWrapper, expr]
+
+ let inner_list_expr = mkApps usingExpr' ((Type binders_tuple_type) : using_args)
+
+ let pat = mkBigLHsVarPatTup binders
+ return (inner_list_expr, pat)
+
+-- This function factors out commonality between the desugaring strategies for GroupStmt.
+-- Given such a statement it gives you back an expression representing how to compute the transformed
+-- list and the tuple that you need to bind from that list in order to proceed with your desugaring
+dsGroupStmt :: Stmt Id -> DsM (CoreExpr, LPat Id)
+dsGroupStmt (GroupStmt (stmts, binderMap) groupByClause) = do
+ let (fromBinders, toBinders) = unzip binderMap
+
+ fromBindersTypes = map idType fromBinders
+ toBindersTypes = map idType toBinders
+
+ toBindersTupleType = mkBigCoreTupTy toBindersTypes
+
+ -- Desugar an inner comprehension which outputs a list of tuples of the "from" binders
+ (expr, fromBindersTupleType) <- dsInnerListComp (stmts, fromBinders)
+
+ -- Work out what arguments should be supplied to that expression: i.e. is an extraction
+ -- function required? If so, create that desugared function and add to arguments
+ (usingExpr', usingArgs) <-
+ case groupByClause of
+ GroupByNothing usingExpr -> liftM2 (,) (dsLExpr usingExpr) (return [expr])
+ GroupBySomething usingExpr byExpr -> do
+ usingExpr' <- dsLExpr (either id noLoc usingExpr)
+
+ byExpr' <- dsLExpr byExpr
+
+ us <- newUniqueSupply
+ [fromBindersTuple] <- newSysLocalsDs [fromBindersTupleType]
+ let byExprWrapper = mkTupleCase us fromBinders byExpr' fromBindersTuple (Var fromBindersTuple)
+
+ return (usingExpr', [Lam fromBindersTuple byExprWrapper, expr])
+
+ -- Create an unzip function for the appropriate arity and element types and find "map"
+ (unzip_fn, unzip_rhs) <- mkUnzipBind fromBindersTypes
+ map_id <- dsLookupGlobalId mapName
+
+ -- Generate the expressions to build the grouped list
+ let -- First we apply the grouping function to the inner list
+ inner_list_expr = mkApps usingExpr' ((Type fromBindersTupleType) : usingArgs)
+ -- Then we map our "unzip" across it to turn the lists of tuples into tuples of lists
+ -- We make sure we instantiate the type variable "a" to be a list of "from" tuples and
+ -- the "b" to be a tuple of "to" lists!
+ unzipped_inner_list_expr = mkApps (Var map_id)
+ [Type (mkListTy fromBindersTupleType), Type toBindersTupleType, Var unzip_fn, inner_list_expr]
+ -- Then finally we bind the unzip function around that expression
+ bound_unzipped_inner_list_expr = Let (Rec [(unzip_fn, unzip_rhs)]) unzipped_inner_list_expr
+
+ -- Build a pattern that ensures the consumer binds into the NEW binders, which hold lists rather than single values
+ let pat = mkBigLHsVarPatTup toBinders
+ return (bound_unzipped_inner_list_expr, pat)
+
\end{code}
%************************************************************************
with the Unboxed variety.
\begin{code}
+
deListComp :: [Stmt Id] -> LHsExpr Id -> CoreExpr -> DsM CoreExpr
deListComp (ParStmt stmtss_w_bndrs : quals) body list
- = mappM do_list_comp stmtss_w_bndrs `thenDs` \ exps ->
- mkZipBind qual_tys `thenDs` \ (zip_fn, zip_rhs) ->
+ = do
+ exps_and_qual_tys <- mappM dsInnerListComp stmtss_w_bndrs
+ let (exps, qual_tys) = unzip exps_and_qual_tys
+
+ (zip_fn, zip_rhs) <- mkZipBind qual_tys
-- Deal with [e | pat <- zip l1 .. ln] in example above
deBindComp pat (Let (Rec [(zip_fn, zip_rhs)]) (mkApps (Var zip_fn) exps))
bndrs_s = map snd stmtss_w_bndrs
-- pat is the pattern ((x1,..,xn), (y1,..,ym)) in the example above
- pat = mkTuplePat pats
- pats = map mk_hs_tuple_pat bndrs_s
-
- -- Types of (x1,..,xn), (y1,..,yn) etc
- qual_tys = map mk_bndrs_tys bndrs_s
-
- do_list_comp (stmts, bndrs)
- = dsListComp stmts (mk_hs_tuple_expr bndrs)
- (mk_bndrs_tys bndrs)
-
- mk_bndrs_tys bndrs = mkCoreTupTy (map idType bndrs)
+ pat = mkBigLHsPatTup pats
+ pats = map mkBigLHsVarPatTup bndrs_s
-- Last: the one to return
deListComp [] body list -- Figure 7.4, SLPJ, p 135, rule C above
= deListComp quals body list `thenDs` \ core_rest ->
dsLocalBinds binds core_rest
+deListComp (stmt@(TransformStmt _ _ _) : quals) body list = do
+ (inner_list_expr, pat) <- dsTransformStmt stmt
+ deBindComp pat inner_list_expr quals body list
+
+deListComp (stmt@(GroupStmt _ _) : quals) body list = do
+ (inner_list_expr, pat) <- dsGroupStmt stmt
+ deBindComp pat inner_list_expr quals body list
+
deListComp (BindStmt pat list1 _ _ : quals) body core_list2 -- rule A' above
= dsLExpr list1 `thenDs` \ core_list1 ->
deBindComp pat core_list1 quals body core_list2
\begin{code}
-deBindComp pat core_list1 quals body core_list2
- = let
- u3_ty@u1_ty = exprType core_list1 -- two names, same thing
+deBindComp pat core_list1 quals body core_list2 = do
+ let
+ u3_ty@u1_ty = exprType core_list1 -- two names, same thing
- -- u1_ty is a [alpha] type, and u2_ty = alpha
- u2_ty = hsLPatType pat
+ -- u1_ty is a [alpha] type, and u2_ty = alpha
+ u2_ty = hsLPatType pat
- 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] ->
+ res_ty = exprType core_list2
+ h_ty = u1_ty `mkFunTy` res_ty
+
+ [h, u1, u2, u3] <- newSysLocalsDs [h_ty, u1_ty, u2_ty, u3_ty]
-- the "fail" value ...
let
- core_fail = App (Var h) (Var u3)
- letrec_body = App (Var h) core_list1
- in
- deListComp quals body core_fail `thenDs` \ rest_expr ->
- matchSimply (Var u2) (StmtCtxt ListComp) pat
- rest_expr core_fail `thenDs` \ core_match ->
+ core_fail = App (Var h) (Var u3)
+ letrec_body = App (Var h) core_list1
+
+ rest_expr <- deListComp quals body core_fail
+ core_match <- matchSimply (Var u2) (StmtCtxt ListComp) pat rest_expr core_fail
+
let
- rhs = Lam u1 $
+ rhs = Lam u1 $
Case (Var u1) u1 res_ty
[(DataAlt nilDataCon, [], core_list2),
(DataAlt consDataCon, [u2, u3], core_match)]
-- Increasing order of tag
- in
- returnDs (Let (Rec [(h, rhs)]) letrec_body)
-\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
- = mappM newSysLocalDs list_tys `thenDs` \ ass ->
- mappM newSysLocalDs elt_tys `thenDs` \ as' ->
- mappM newSysLocalDs list_tys `thenDs` \ as's ->
- newSysLocalDs zip_fn_ty `thenDs` \ zip_fn ->
- let
- inner_rhs = mkConsExpr ret_elt_ty
- (mkCoreTup (map Var 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 = mkCoreTupTy elt_tys
- list_ret_ty = mkListTy ret_elt_ty
- zip_fn_ty = mkFunTys list_tys list_ret_ty
-
- mk_case (as, a', as') rest
- = Case (Var as) as list_ret_ty
- [(DataAlt nilDataCon, [], mkNilExpr ret_elt_ty),
- (DataAlt consDataCon, [a', as'], rest)]
- -- Increasing order of tag
--- Helper functions that makes an HsTuple only for non-1-sized tuples
-mk_hs_tuple_expr :: [Id] -> LHsExpr Id
-mk_hs_tuple_expr [] = nlHsVar unitDataConId
-mk_hs_tuple_expr [id] = nlHsVar id
-mk_hs_tuple_expr ids = noLoc $ ExplicitTuple [ nlHsVar i | i <- ids ] Boxed
-
-mk_hs_tuple_pat :: [Id] -> LPat Id
-mk_hs_tuple_pat bs = mkTuplePat (map nlVarPat bs)
+
+ return (Let (Rec [(h, rhs)]) letrec_body)
\end{code}
-
%************************************************************************
%* *
\subsection[DsListComp-foldr-build]{Foldr/Build desugaring of list comprehensions}
\end{verbatim}
\begin{code}
-dfListComp :: Id -> Id -- 'c' and 'n'
- -> [Stmt Id] -- the rest of the qual's
- -> LHsExpr Id
- -> DsM CoreExpr
+dfListComp :: Id -> Id -- 'c' and 'n'
+ -> [Stmt Id] -- the rest of the qual's
+ -> LHsExpr Id
+ -> DsM CoreExpr
-- Last: the one to return
dfListComp c_id n_id [] body
= dfListComp c_id n_id quals body `thenDs` \ core_rest ->
dsLocalBinds binds core_rest
-dfListComp c_id n_id (BindStmt pat list1 _ _ : quals) body
+dfListComp c_id n_id (stmt@(TransformStmt _ _ _) : quals) body = do
+ (inner_list_expr, pat) <- dsTransformStmt stmt
+ -- Anyway, we bind the newly transformed list via the generic binding function
+ dfBindComp c_id n_id (pat, inner_list_expr) quals body
+
+dfListComp c_id n_id (stmt@(GroupStmt _ _) : quals) body = do
+ (inner_list_expr, pat) <- dsGroupStmt stmt
+ -- Anyway, we bind the newly grouped list via the generic binding function
+ dfBindComp c_id n_id (pat, inner_list_expr) quals body
+
+dfListComp c_id n_id (BindStmt pat list1 _ _ : quals) body = do
-- evaluate the two lists
- = dsLExpr list1 `thenDs` \ core_list1 ->
-
+ core_list1 <- dsLExpr list1
+
+ -- Do the rest of the work in the generic binding builder
+ dfBindComp c_id n_id (pat, core_list1) quals body
+
+dfBindComp :: Id -> Id -- 'c' and 'n'
+ -> (LPat Id, CoreExpr)
+ -> [Stmt Id] -- the rest of the qual's
+ -> LHsExpr Id
+ -> DsM CoreExpr
+dfBindComp c_id n_id (pat, core_list1) quals body = do
-- find the required type
let x_ty = hsLPatType pat
- b_ty = idType n_id
- in
+ b_ty = idType n_id
-- create some new local id's
- newSysLocalsDs [b_ty,x_ty] `thenDs` \ [b,x] ->
+ [b, x] <- newSysLocalsDs [b_ty, x_ty]
-- build rest of the comprehesion
- dfListComp c_id b quals body `thenDs` \ core_rest ->
+ core_rest <- dfListComp c_id b quals body
-- build the pattern match
- matchSimply (Var x) (StmtCtxt ListComp)
- pat core_rest (Var b) `thenDs` \ core_expr ->
+ core_expr <- matchSimply (Var x) (StmtCtxt ListComp)
+ pat core_rest (Var b)
-- now build the outermost foldr, and return
- dsLookupGlobalId foldrName `thenDs` \ foldr_id ->
- returnDs (
- Var foldr_id `App` Type x_ty
- `App` Type b_ty
- `App` mkLams [x, b] core_expr
- `App` Var n_id
- `App` core_list1
- )
+ foldr_id <- dsLookupGlobalId foldrName
+ return (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}
+
+%************************************************************************
+%* *
+\subsection[DsFunGeneration]{Generation of zip/unzip functions for use in desugaring}
+%* *
+%************************************************************************
+
+\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) -> (a1, a2) : zip as'1 as'2)]
+
+mkZipBind elt_tys = do
+ ass <- mappM newSysLocalDs elt_list_tys
+ as' <- mappM newSysLocalDs elt_tys
+ as's <- mappM newSysLocalDs elt_list_tys
+
+ zip_fn <- newSysLocalDs zip_fn_ty
+
+ let inner_rhs = mkConsExpr elt_tuple_ty
+ (mkBigCoreVarTup as')
+ (mkVarApps (Var zip_fn) as's)
+ zip_body = foldr mk_case inner_rhs (zip3 ass as' as's)
+
+ return (zip_fn, mkLams ass zip_body)
+ where
+ elt_list_tys = map mkListTy elt_tys
+ elt_tuple_ty = mkBigCoreTupTy elt_tys
+ elt_tuple_list_ty = mkListTy elt_tuple_ty
+
+ zip_fn_ty = mkFunTys elt_list_tys elt_tuple_list_ty
+
+ mk_case (as, a', as') rest
+ = Case (Var as) as elt_tuple_list_ty
+ [(DataAlt nilDataCon, [], mkNilExpr elt_tuple_ty),
+ (DataAlt consDataCon, [a', as'], rest)]
+ -- Increasing order of tag
+
+
+mkUnzipBind :: [Type] -> DsM (Id, CoreExpr)
+-- mkUnzipBind [t1, t2]
+-- = (unzip, \ys :: [(t1, t2)] -> foldr (\ax :: (t1, t2) axs :: ([t1], [t2])
+-- -> case ax of
+-- (x1, x2) -> case axs of
+-- (xs1, xs2) -> (x1 : xs1, x2 : xs2))
+-- ([], [])
+-- ys)
+--
+-- We use foldr here in all cases, even if rules are turned off, because we may as well!
+mkUnzipBind elt_tys = do
+ ax <- newSysLocalDs elt_tuple_ty
+ axs <- newSysLocalDs elt_list_tuple_ty
+ ys <- newSysLocalDs elt_tuple_list_ty
+ xs <- mappM newSysLocalDs elt_tys
+ xss <- mappM newSysLocalDs elt_list_tys
+
+ unzip_fn <- newSysLocalDs unzip_fn_ty
+
+ foldr_id <- dsLookupGlobalId foldrName
+ [us1, us2] <- sequence [newUniqueSupply, newUniqueSupply]
+
+ let nil_tuple = mkBigCoreTup (map mkNilExpr elt_tys)
+
+ concat_expressions = map mkConcatExpression (zip3 elt_tys (map Var xs) (map Var xss))
+ tupled_concat_expression = mkBigCoreTup concat_expressions
+
+ folder_body_inner_case = mkTupleCase us1 xss tupled_concat_expression axs (Var axs)
+ folder_body_outer_case = mkTupleCase us2 xs folder_body_inner_case ax (Var ax)
+ folder_body = mkLams [ax, axs] folder_body_outer_case
+
+ unzip_body = mkApps (Var foldr_id) [Type elt_tuple_ty, Type elt_list_tuple_ty, folder_body, nil_tuple, Var ys]
+ unzip_body_saturated = mkLams [ys] unzip_body
+
+ return (unzip_fn, unzip_body_saturated)
+ where
+ elt_tuple_ty = mkBigCoreTupTy elt_tys
+ elt_tuple_list_ty = mkListTy elt_tuple_ty
+ elt_list_tys = map mkListTy elt_tys
+ elt_list_tuple_ty = mkBigCoreTupTy elt_list_tys
+
+ unzip_fn_ty = elt_tuple_list_ty `mkFunTy` elt_list_tuple_ty
+
+ mkConcatExpression (list_element_ty, head, tail) = mkConsExpr list_element_ty head tail
+
+
+
\end{code}
%************************************************************************
--
-- [:e | qss:] = <<[:e | qss:]>> () [:():]
--
-dsPArrComp :: [Stmt Id]
- -> LHsExpr Id
- -> Type -- Don't use; called with `undefined' below
- -> DsM CoreExpr
+dsPArrComp :: [Stmt Id]
+ -> LHsExpr Id
+ -> Type -- Don't use; called with `undefined' below
+ -> DsM CoreExpr
dsPArrComp [ParStmt qss] body _ = -- parallel comprehension
dePArrParComp qss body
dsPArrComp qs body _ = -- no ParStmt in `qs'
- dsLookupGlobalId replicatePName `thenDs` \repP ->
- let unitArray = mkApps (Var repP) [Type unitTy,
- mkIntExpr 1,
+ dsLookupGlobalId singletonPName `thenDs` \sglP ->
+ let unitArray = mkApps (Var sglP) [Type unitTy,
mkCoreTup []]
in
- dePArrComp qs body (mkTuplePat []) unitArray
+ dePArrComp qs body (mkLHsPatTup []) unitArray
in
deLambda ty pa b `thenDs` \(clam,_) ->
dePArrComp qs body pa (mkApps (Var filterP) [Type ty, clam, cea])
+
+--
+-- <<[:e' | p <- e, qs:]>> pa ea =
+-- let ef = \pa -> e
+-- in
+-- <<[:e' | qs:]>> (pa, p) (crossMap ea ef)
+--
+-- if matching again p cannot fail, or else
--
-- <<[:e' | p <- e, qs:]>> pa ea =
-- let ef = \pa -> filterP (\x -> case x of {p -> True; _ -> False}) e
in
newSysLocalDs ety'ce `thenDs` \v ->
matchSimply (Var v) (StmtCtxt PArrComp) p true false `thenDs` \pred ->
- let cef = mkApps (Var filterP) [Type ety'ce, mkLams [v] pred, ce]
+ let cef | isIrrefutableHsPat p = ce
+ | otherwise = mkApps (Var filterP) [Type ety'ce, mkLams [v] pred, ce]
in
mkLambda ety'cea pa cef `thenDs` \(clam,
_ ) ->
let ety'cef = ety'ce -- filter doesn't change the element type
- pa' = mkTuplePat [pa, p]
+ pa' = mkLHsPatTup [pa, p]
in
dePArrComp qs body pa' (mkApps (Var crossMapP)
[Type ety'cea, Type ety'cef, cea, clam])
in
mkErrorAppDs pAT_ERROR_ID errTy errMsg `thenDs` \cerr ->
matchSimply (Var v) (StmtCtxt PArrComp) pa projBody cerr`thenDs` \ccase ->
- let pa' = mkTuplePat [pa, mkTuplePat (map nlVarPat xs)]
+ let pa' = mkLHsPatTup [pa, mkLHsPatTup (map nlVarPat xs)]
proj = mkLams [v] ccase
in
dePArrComp qs body pa' (mkApps (Var mapP)
-- empty parallel statement lists have no source representation
panic "DsListComp.dePArrComp: Empty parallel list comprehension"
deParStmt ((qs, xs):qss) = -- first statement
- let res_expr = mkExplicitTuple (map nlHsVar xs)
+ let res_expr = mkLHsVarTup xs
in
dsPArrComp (map unLoc qs) res_expr undefined `thenDs` \cqs ->
- parStmts qss (mkTuplePat (map nlVarPat xs)) cqs
+ parStmts qss (mkLHsVarPatTup xs) cqs
---
parStmts [] pa cea = return (pa, cea)
parStmts ((qs, xs):qss) pa cea = -- subsequent statements (zip'ed)
dsLookupGlobalId zipPName `thenDs` \zipP ->
- let pa' = mkTuplePat [pa, mkTuplePat (map nlVarPat xs)]
+ let pa' = mkLHsPatTup [pa, mkLHsVarPatTup xs]
ty'cea = parrElemType cea
- res_expr = mkExplicitTuple (map nlHsVar xs)
+ res_expr = mkLHsVarTup xs
in
dsPArrComp (map unLoc qs) res_expr undefined `thenDs` \cqs ->
let ty'cqs = parrElemType cqs
Just (tycon, [ty]) | tycon == parrTyCon -> ty
_ -> panic
"DsListComp.parrElemType: not a parallel array type"
-
--- Smart constructor for source tuple patterns
---
-mkTuplePat :: [LPat Id] -> LPat Id
-mkTuplePat [lpat] = lpat
-mkTuplePat lpats = noLoc $ mkVanillaTuplePat lpats Boxed
-
--- Smart constructor for source tuple expressions
---
-mkExplicitTuple :: [LHsExpr id] -> LHsExpr id
-mkExplicitTuple [lexp] = lexp
-mkExplicitTuple lexps = noLoc $ ExplicitTuple lexps Boxed
\end{code}