2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Desugaring list comprehensions and array comprehensions
9 {-# OPTIONS -fno-warn-incomplete-patterns #-}
10 -- The above warning supression flag is a temporary kludge.
11 -- While working on this module you are encouraged to remove it and fix
12 -- any warnings in the module. See
13 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
16 module DsListComp ( dsListComp, dsPArrComp ) where
18 #include "HsVersions.h"
20 import {-# SOURCE #-} DsExpr ( dsLExpr, dsLocalBinds )
27 import DsMonad -- the monadery used in the desugarer
42 import Control.Monad ( liftM2 )
45 List comprehensions may be desugared in one of two ways: ``ordinary''
46 (as you would expect if you read SLPJ's book) and ``with foldr/build
47 turned on'' (if you read Gill {\em et al.}'s paper on the subject).
49 There will be at least one ``qualifier'' in the input.
52 dsListComp :: [LStmt Id]
54 -> Type -- Type of list elements
56 dsListComp lquals body elt_ty = do
58 let quals = map unLoc lquals
60 if not (dopt Opt_EnableRewriteRules dflags) || dopt Opt_IgnoreInterfacePragmas dflags
61 -- Either rules are switched off, or we are ignoring what there are;
62 -- Either way foldr/build won't happen, so use the more efficient
63 -- Wadler-style desugaring
64 || isParallelComp quals
65 -- Foldr-style desugaring can't handle parallel list comprehensions
66 then deListComp quals body (mkNilExpr elt_ty)
67 else mkBuildExpr elt_ty (\(c, _) (n, _) -> dfListComp c n quals body)
68 -- Foldr/build should be enabled, so desugar
69 -- into foldrs and builds
72 -- We must test for ParStmt anywhere, not just at the head, because an extension
73 -- to list comprehensions would be to add brackets to specify the associativity
74 -- of qualifier lists. This is really easy to do by adding extra ParStmts into the
75 -- mix of possibly a single element in length, so we do this to leave the possibility open
76 isParallelComp = any isParallelStmt
78 isParallelStmt (ParStmt _) = True
79 isParallelStmt _ = False
82 -- This function lets you desugar a inner list comprehension and a list of the binders
83 -- of that comprehension that we need in the outer comprehension into such an expression
84 -- and the type of the elements that it outputs (tuples of binders)
85 dsInnerListComp :: ([LStmt Id], [Id]) -> DsM (CoreExpr, Type)
86 dsInnerListComp (stmts, bndrs) = do
87 expr <- dsListComp stmts (mkBigLHsVarTup bndrs) bndrs_tuple_type
88 return (expr, bndrs_tuple_type)
90 bndrs_types = map idType bndrs
91 bndrs_tuple_type = mkBigCoreTupTy bndrs_types
94 -- This function factors out commonality between the desugaring strategies for TransformStmt.
95 -- Given such a statement it gives you back an expression representing how to compute the transformed
96 -- list and the tuple that you need to bind from that list in order to proceed with your desugaring
97 dsTransformStmt :: Stmt Id -> DsM (CoreExpr, LPat Id)
98 dsTransformStmt (TransformStmt (stmts, binders) usingExpr maybeByExpr) = do
99 (expr, binders_tuple_type) <- dsInnerListComp (stmts, binders)
100 usingExpr' <- dsLExpr usingExpr
104 Nothing -> return [expr]
106 byExpr' <- dsLExpr byExpr
108 us <- newUniqueSupply
109 [tuple_binder] <- newSysLocalsDs [binders_tuple_type]
110 let byExprWrapper = mkTupleCase us binders byExpr' tuple_binder (Var tuple_binder)
112 return [Lam tuple_binder byExprWrapper, expr]
114 let inner_list_expr = mkApps usingExpr' ((Type binders_tuple_type) : using_args)
116 let pat = mkBigLHsVarPatTup binders
117 return (inner_list_expr, pat)
119 -- This function factors out commonality between the desugaring strategies for GroupStmt.
120 -- Given such a statement it gives you back an expression representing how to compute the transformed
121 -- list and the tuple that you need to bind from that list in order to proceed with your desugaring
122 dsGroupStmt :: Stmt Id -> DsM (CoreExpr, LPat Id)
123 dsGroupStmt (GroupStmt (stmts, binderMap) groupByClause) = do
124 let (fromBinders, toBinders) = unzip binderMap
126 fromBindersTypes = map idType fromBinders
127 toBindersTypes = map idType toBinders
129 toBindersTupleType = mkBigCoreTupTy toBindersTypes
131 -- Desugar an inner comprehension which outputs a list of tuples of the "from" binders
132 (expr, fromBindersTupleType) <- dsInnerListComp (stmts, fromBinders)
134 -- Work out what arguments should be supplied to that expression: i.e. is an extraction
135 -- function required? If so, create that desugared function and add to arguments
136 (usingExpr', usingArgs) <-
137 case groupByClause of
138 GroupByNothing usingExpr -> liftM2 (,) (dsLExpr usingExpr) (return [expr])
139 GroupBySomething usingExpr byExpr -> do
140 usingExpr' <- dsLExpr (either id noLoc usingExpr)
142 byExpr' <- dsLExpr byExpr
144 us <- newUniqueSupply
145 [fromBindersTuple] <- newSysLocalsDs [fromBindersTupleType]
146 let byExprWrapper = mkTupleCase us fromBinders byExpr' fromBindersTuple (Var fromBindersTuple)
148 return (usingExpr', [Lam fromBindersTuple byExprWrapper, expr])
150 -- Create an unzip function for the appropriate arity and element types and find "map"
151 (unzip_fn, unzip_rhs) <- mkUnzipBind fromBindersTypes
152 map_id <- dsLookupGlobalId mapName
154 -- Generate the expressions to build the grouped list
155 let -- First we apply the grouping function to the inner list
156 inner_list_expr = mkApps usingExpr' ((Type fromBindersTupleType) : usingArgs)
157 -- Then we map our "unzip" across it to turn the lists of tuples into tuples of lists
158 -- We make sure we instantiate the type variable "a" to be a list of "from" tuples and
159 -- the "b" to be a tuple of "to" lists!
160 unzipped_inner_list_expr = mkApps (Var map_id)
161 [Type (mkListTy fromBindersTupleType), Type toBindersTupleType, Var unzip_fn, inner_list_expr]
162 -- Then finally we bind the unzip function around that expression
163 bound_unzipped_inner_list_expr = Let (Rec [(unzip_fn, unzip_rhs)]) unzipped_inner_list_expr
165 -- Build a pattern that ensures the consumer binds into the NEW binders, which hold lists rather than single values
166 let pat = mkBigLHsVarPatTup toBinders
167 return (bound_unzipped_inner_list_expr, pat)
171 %************************************************************************
173 \subsection[DsListComp-ordinary]{Ordinary desugaring of list comprehensions}
175 %************************************************************************
177 Just as in Phil's chapter~7 in SLPJ, using the rules for
178 optimally-compiled list comprehensions. This is what Kevin followed
179 as well, and I quite happily do the same. The TQ translation scheme
180 transforms a list of qualifiers (either boolean expressions or
181 generators) into a single expression which implements the list
182 comprehension. Because we are generating 2nd-order polymorphic
183 lambda-calculus, calls to NIL and CONS must be applied to a type
184 argument, as well as their usual value arguments.
186 TE << [ e | qs ] >> = TQ << [ e | qs ] ++ Nil (typeOf e) >>
189 TQ << [ e | ] ++ L >> = Cons (typeOf e) TE <<e>> TE <<L>>
192 TQ << [ e | b , qs ] ++ L >> =
193 if TE << b >> then TQ << [ e | qs ] ++ L >> else TE << L >>
196 TQ << [ e | p <- L1, qs ] ++ L2 >> =
202 (( \ TE << p >> -> ( TQ << [e | qs] ++ (h u3) >> )) u2)
207 "h", "u1", "u2", and "u3" are new variables.
210 @deListComp@ is the TQ translation scheme. Roughly speaking, @dsExpr@
211 is the TE translation scheme. Note that we carry around the @L@ list
212 already desugared. @dsListComp@ does the top TE rule mentioned above.
214 To the above, we add an additional rule to deal with parallel list
215 comprehensions. The translation goes roughly as follows:
216 [ e | p1 <- e11, let v1 = e12, p2 <- e13
217 | q1 <- e21, let v2 = e22, q2 <- e23]
219 [ e | ((x1, .., xn), (y1, ..., ym)) <-
220 zip [(x1,..,xn) | p1 <- e11, let v1 = e12, p2 <- e13]
221 [(y1,..,ym) | q1 <- e21, let v2 = e22, q2 <- e23]]
222 where (x1, .., xn) are the variables bound in p1, v1, p2
223 (y1, .., ym) are the variables bound in q1, v2, q2
225 In the translation below, the ParStmt branch translates each parallel branch
226 into a sub-comprehension, and desugars each independently. The resulting lists
227 are fed to a zip function, we create a binding for all the variables bound in all
228 the comprehensions, and then we hand things off the the desugarer for bindings.
229 The zip function is generated here a) because it's small, and b) because then we
230 don't have to deal with arbitrary limits on the number of zip functions in the
231 prelude, nor which library the zip function came from.
232 The introduced tuples are Boxed, but only because I couldn't get it to work
233 with the Unboxed variety.
237 deListComp :: [Stmt Id] -> LHsExpr Id -> CoreExpr -> DsM CoreExpr
239 deListComp (ParStmt stmtss_w_bndrs : quals) body list
241 exps_and_qual_tys <- mapM dsInnerListComp stmtss_w_bndrs
242 let (exps, qual_tys) = unzip exps_and_qual_tys
244 (zip_fn, zip_rhs) <- mkZipBind qual_tys
246 -- Deal with [e | pat <- zip l1 .. ln] in example above
247 deBindComp pat (Let (Rec [(zip_fn, zip_rhs)]) (mkApps (Var zip_fn) exps))
251 bndrs_s = map snd stmtss_w_bndrs
253 -- pat is the pattern ((x1,..,xn), (y1,..,ym)) in the example above
254 pat = mkBigLHsPatTup pats
255 pats = map mkBigLHsVarPatTup bndrs_s
257 -- Last: the one to return
258 deListComp [] body list = do -- Figure 7.4, SLPJ, p 135, rule C above
259 core_body <- dsLExpr body
260 return (mkConsExpr (exprType core_body) core_body list)
262 -- Non-last: must be a guard
263 deListComp (ExprStmt guard _ _ : quals) body list = do -- rule B above
264 core_guard <- dsLExpr guard
265 core_rest <- deListComp quals body list
266 return (mkIfThenElse core_guard core_rest list)
268 -- [e | let B, qs] = let B in [e | qs]
269 deListComp (LetStmt binds : quals) body list = do
270 core_rest <- deListComp quals body list
271 dsLocalBinds binds core_rest
273 deListComp (stmt@(TransformStmt _ _ _) : quals) body list = do
274 (inner_list_expr, pat) <- dsTransformStmt stmt
275 deBindComp pat inner_list_expr quals body list
277 deListComp (stmt@(GroupStmt _ _) : quals) body list = do
278 (inner_list_expr, pat) <- dsGroupStmt stmt
279 deBindComp pat inner_list_expr quals body list
281 deListComp (BindStmt pat list1 _ _ : quals) body core_list2 = do -- rule A' above
282 core_list1 <- dsLExpr list1
283 deBindComp pat core_list1 quals body core_list2
288 deBindComp :: OutPat Id
294 deBindComp pat core_list1 quals body core_list2 = do
296 u3_ty@u1_ty = exprType core_list1 -- two names, same thing
298 -- u1_ty is a [alpha] type, and u2_ty = alpha
299 u2_ty = hsLPatType pat
301 res_ty = exprType core_list2
302 h_ty = u1_ty `mkFunTy` res_ty
304 [h, u1, u2, u3] <- newSysLocalsDs [h_ty, u1_ty, u2_ty, u3_ty]
306 -- the "fail" value ...
308 core_fail = App (Var h) (Var u3)
309 letrec_body = App (Var h) core_list1
311 rest_expr <- deListComp quals body core_fail
312 core_match <- matchSimply (Var u2) (StmtCtxt ListComp) pat rest_expr core_fail
316 Case (Var u1) u1 res_ty
317 [(DataAlt nilDataCon, [], core_list2),
318 (DataAlt consDataCon, [u2, u3], core_match)]
319 -- Increasing order of tag
321 return (Let (Rec [(h, rhs)]) letrec_body)
324 %************************************************************************
326 \subsection[DsListComp-foldr-build]{Foldr/Build desugaring of list comprehensions}
328 %************************************************************************
330 @dfListComp@ are the rules used with foldr/build turned on:
333 TE[ e | ] c n = c e n
334 TE[ e | b , q ] c n = if b then TE[ e | q ] c n else n
335 TE[ e | p <- l , q ] c n = let
336 f = \ x b -> case x of
344 dfListComp :: Id -> Id -- 'c' and 'n'
345 -> [Stmt Id] -- the rest of the qual's
349 -- Last: the one to return
350 dfListComp c_id n_id [] body = do
351 core_body <- dsLExpr body
352 return (mkApps (Var c_id) [core_body, Var n_id])
354 -- Non-last: must be a guard
355 dfListComp c_id n_id (ExprStmt guard _ _ : quals) body = do
356 core_guard <- dsLExpr guard
357 core_rest <- dfListComp c_id n_id quals body
358 return (mkIfThenElse core_guard core_rest (Var n_id))
360 dfListComp c_id n_id (LetStmt binds : quals) body = do
361 -- new in 1.3, local bindings
362 core_rest <- dfListComp c_id n_id quals body
363 dsLocalBinds binds core_rest
365 dfListComp c_id n_id (stmt@(TransformStmt _ _ _) : quals) body = do
366 (inner_list_expr, pat) <- dsTransformStmt stmt
367 -- Anyway, we bind the newly transformed list via the generic binding function
368 dfBindComp c_id n_id (pat, inner_list_expr) quals body
370 dfListComp c_id n_id (stmt@(GroupStmt _ _) : quals) body = do
371 (inner_list_expr, pat) <- dsGroupStmt stmt
372 -- Anyway, we bind the newly grouped list via the generic binding function
373 dfBindComp c_id n_id (pat, inner_list_expr) quals body
375 dfListComp c_id n_id (BindStmt pat list1 _ _ : quals) body = do
376 -- evaluate the two lists
377 core_list1 <- dsLExpr list1
379 -- Do the rest of the work in the generic binding builder
380 dfBindComp c_id n_id (pat, core_list1) quals body
382 dfBindComp :: Id -> Id -- 'c' and 'n'
383 -> (LPat Id, CoreExpr)
384 -> [Stmt Id] -- the rest of the qual's
387 dfBindComp c_id n_id (pat, core_list1) quals body = do
388 -- find the required type
389 let x_ty = hsLPatType pat
392 -- create some new local id's
393 [b, x] <- newSysLocalsDs [b_ty, x_ty]
395 -- build rest of the comprehesion
396 core_rest <- dfListComp c_id b quals body
398 -- build the pattern match
399 core_expr <- matchSimply (Var x) (StmtCtxt ListComp)
400 pat core_rest (Var b)
402 -- now build the outermost foldr, and return
403 mkFoldrExpr x_ty b_ty (mkLams [x, b] core_expr) (Var n_id) core_list1
406 %************************************************************************
408 \subsection[DsFunGeneration]{Generation of zip/unzip functions for use in desugaring}
410 %************************************************************************
414 mkZipBind :: [Type] -> DsM (Id, CoreExpr)
415 -- mkZipBind [t1, t2]
416 -- = (zip, \as1:[t1] as2:[t2]
419 -- (a1:as'1) -> case as2 of
421 -- (a2:as'2) -> (a1, a2) : zip as'1 as'2)]
423 mkZipBind elt_tys = do
424 ass <- mapM newSysLocalDs elt_list_tys
425 as' <- mapM newSysLocalDs elt_tys
426 as's <- mapM newSysLocalDs elt_list_tys
428 zip_fn <- newSysLocalDs zip_fn_ty
430 let inner_rhs = mkConsExpr elt_tuple_ty
431 (mkBigCoreVarTup as')
432 (mkVarApps (Var zip_fn) as's)
433 zip_body = foldr mk_case inner_rhs (zip3 ass as' as's)
435 return (zip_fn, mkLams ass zip_body)
437 elt_list_tys = map mkListTy elt_tys
438 elt_tuple_ty = mkBigCoreTupTy elt_tys
439 elt_tuple_list_ty = mkListTy elt_tuple_ty
441 zip_fn_ty = mkFunTys elt_list_tys elt_tuple_list_ty
443 mk_case (as, a', as') rest
444 = Case (Var as) as elt_tuple_list_ty
445 [(DataAlt nilDataCon, [], mkNilExpr elt_tuple_ty),
446 (DataAlt consDataCon, [a', as'], rest)]
447 -- Increasing order of tag
450 mkUnzipBind :: [Type] -> DsM (Id, CoreExpr)
451 -- mkUnzipBind [t1, t2]
452 -- = (unzip, \ys :: [(t1, t2)] -> foldr (\ax :: (t1, t2) axs :: ([t1], [t2])
454 -- (x1, x2) -> case axs of
455 -- (xs1, xs2) -> (x1 : xs1, x2 : xs2))
459 -- We use foldr here in all cases, even if rules are turned off, because we may as well!
460 mkUnzipBind elt_tys = do
461 ax <- newSysLocalDs elt_tuple_ty
462 axs <- newSysLocalDs elt_list_tuple_ty
463 ys <- newSysLocalDs elt_tuple_list_ty
464 xs <- mapM newSysLocalDs elt_tys
465 xss <- mapM newSysLocalDs elt_list_tys
467 unzip_fn <- newSysLocalDs unzip_fn_ty
469 [us1, us2] <- sequence [newUniqueSupply, newUniqueSupply]
471 let nil_tuple = mkBigCoreTup (map mkNilExpr elt_tys)
473 concat_expressions = map mkConcatExpression (zip3 elt_tys (map Var xs) (map Var xss))
474 tupled_concat_expression = mkBigCoreTup concat_expressions
476 folder_body_inner_case = mkTupleCase us1 xss tupled_concat_expression axs (Var axs)
477 folder_body_outer_case = mkTupleCase us2 xs folder_body_inner_case ax (Var ax)
478 folder_body = mkLams [ax, axs] folder_body_outer_case
480 unzip_body <- mkFoldrExpr elt_tuple_ty elt_list_tuple_ty folder_body nil_tuple (Var ys)
481 return (unzip_fn, mkLams [ys] unzip_body)
483 elt_tuple_ty = mkBigCoreTupTy elt_tys
484 elt_tuple_list_ty = mkListTy elt_tuple_ty
485 elt_list_tys = map mkListTy elt_tys
486 elt_list_tuple_ty = mkBigCoreTupTy elt_list_tys
488 unzip_fn_ty = elt_tuple_list_ty `mkFunTy` elt_list_tuple_ty
490 mkConcatExpression (list_element_ty, head, tail) = mkConsExpr list_element_ty head tail
496 %************************************************************************
498 \subsection[DsPArrComp]{Desugaring of array comprehensions}
500 %************************************************************************
504 -- entry point for desugaring a parallel array comprehension
506 -- [:e | qss:] = <<[:e | qss:]>> () [:():]
508 dsPArrComp :: [Stmt Id]
510 -> Type -- Don't use; called with `undefined' below
512 dsPArrComp [ParStmt qss] body _ = -- parallel comprehension
513 dePArrParComp qss body
515 -- Special case for simple generators:
517 -- <<[:e' | p <- e, qs:]>> = <<[: e' | qs :]>> p e
519 -- if matching again p cannot fail, or else
521 -- <<[:e' | p <- e, qs:]>> =
522 -- <<[:e' | qs:]>> p (filterP (\x -> case x of {p -> True; _ -> False}) e)
524 dsPArrComp (BindStmt p e _ _ : qs) body _ = do
525 filterP <- dsLookupGlobalId filterPName
527 let ety'ce = parrElemType ce
528 false = Var falseDataConId
529 true = Var trueDataConId
530 v <- newSysLocalDs ety'ce
531 pred <- matchSimply (Var v) (StmtCtxt PArrComp) p true false
532 let gen | isIrrefutableHsPat p = ce
533 | otherwise = mkApps (Var filterP) [Type ety'ce, mkLams [v] pred, ce]
534 dePArrComp qs body p gen
536 dsPArrComp qs body _ = do -- no ParStmt in `qs'
537 sglP <- dsLookupGlobalId singletonPName
538 let unitArray = mkApps (Var sglP) [Type unitTy, mkCoreTup []]
539 dePArrComp qs body (noLoc $ WildPat unitTy) unitArray
545 dePArrComp :: [Stmt Id]
547 -> LPat Id -- the current generator pattern
548 -> CoreExpr -- the current generator expression
551 -- <<[:e' | :]>> pa ea = mapP (\pa -> e') ea
553 dePArrComp [] e' pa cea = do
554 mapP <- dsLookupGlobalId mapPName
555 let ty = parrElemType cea
556 (clam, ty'e') <- deLambda ty pa e'
557 return $ mkApps (Var mapP) [Type ty, Type ty'e', clam, cea]
559 -- <<[:e' | b, qs:]>> pa ea = <<[:e' | qs:]>> pa (filterP (\pa -> b) ea)
561 dePArrComp (ExprStmt b _ _ : qs) body pa cea = do
562 filterP <- dsLookupGlobalId filterPName
563 let ty = parrElemType cea
564 (clam,_) <- deLambda ty pa b
565 dePArrComp qs body pa (mkApps (Var filterP) [Type ty, clam, cea])
568 -- <<[:e' | p <- e, qs:]>> pa ea =
571 -- <<[:e' | qs:]>> (pa, p) (crossMap ea ef)
573 -- if matching again p cannot fail, or else
575 -- <<[:e' | p <- e, qs:]>> pa ea =
576 -- let ef = \pa -> filterP (\x -> case x of {p -> True; _ -> False}) e
578 -- <<[:e' | qs:]>> (pa, p) (crossMapP ea ef)
580 dePArrComp (BindStmt p e _ _ : qs) body pa cea = do
581 filterP <- dsLookupGlobalId filterPName
582 crossMapP <- dsLookupGlobalId crossMapPName
584 let ety'cea = parrElemType cea
585 ety'ce = parrElemType ce
586 false = Var falseDataConId
587 true = Var trueDataConId
588 v <- newSysLocalDs ety'ce
589 pred <- matchSimply (Var v) (StmtCtxt PArrComp) p true false
590 let cef | isIrrefutableHsPat p = ce
591 | otherwise = mkApps (Var filterP) [Type ety'ce, mkLams [v] pred, ce]
592 (clam, _) <- mkLambda ety'cea pa cef
593 let ety'cef = ety'ce -- filter doesn't change the element type
594 pa' = mkLHsPatTup [pa, p]
596 dePArrComp qs body pa' (mkApps (Var crossMapP)
597 [Type ety'cea, Type ety'cef, cea, clam])
599 -- <<[:e' | let ds, qs:]>> pa ea =
600 -- <<[:e' | qs:]>> (pa, (x_1, ..., x_n))
601 -- (mapP (\v@pa -> let ds in (v, (x_1, ..., x_n))) ea)
603 -- {x_1, ..., x_n} = DV (ds) -- Defined Variables
605 dePArrComp (LetStmt ds : qs) body pa cea = do
606 mapP <- dsLookupGlobalId mapPName
607 let xs = map unLoc (collectLocalBinders ds)
608 ty'cea = parrElemType cea
609 v <- newSysLocalDs ty'cea
610 clet <- dsLocalBinds ds (mkCoreTup (map Var xs))
611 let'v <- newSysLocalDs (exprType clet)
612 let projBody = mkCoreLet (NonRec let'v clet) $
613 mkCoreTup [Var v, Var let'v]
614 errTy = exprType projBody
615 errMsg = ptext (sLit "DsListComp.dePArrComp: internal error!")
616 cerr <- mkErrorAppDs pAT_ERROR_ID errTy errMsg
617 ccase <- matchSimply (Var v) (StmtCtxt PArrComp) pa projBody cerr
618 let pa' = mkLHsPatTup [pa, mkLHsPatTup (map nlVarPat xs)]
619 proj = mkLams [v] ccase
620 dePArrComp qs body pa' (mkApps (Var mapP)
621 [Type ty'cea, Type errTy, proj, cea])
623 -- The parser guarantees that parallel comprehensions can only appear as
624 -- singeltons qualifier lists, which we already special case in the caller.
625 -- So, encountering one here is a bug.
627 dePArrComp (ParStmt _ : _) _ _ _ =
628 panic "DsListComp.dePArrComp: malformed comprehension AST"
630 -- <<[:e' | qs | qss:]>> pa ea =
631 -- <<[:e' | qss:]>> (pa, (x_1, ..., x_n))
632 -- (zipP ea <<[:(x_1, ..., x_n) | qs:]>>)
634 -- {x_1, ..., x_n} = DV (qs)
636 dePArrParComp :: [([LStmt Id], [Id])] -> LHsExpr Id -> DsM CoreExpr
637 dePArrParComp qss body = do
638 (pQss, ceQss) <- deParStmt qss
639 dePArrComp [] body pQss ceQss
642 -- empty parallel statement lists have no source representation
643 panic "DsListComp.dePArrComp: Empty parallel list comprehension"
644 deParStmt ((qs, xs):qss) = do -- first statement
645 let res_expr = mkLHsVarTup xs
646 cqs <- dsPArrComp (map unLoc qs) res_expr undefined
647 parStmts qss (mkLHsVarPatTup xs) cqs
649 parStmts [] pa cea = return (pa, cea)
650 parStmts ((qs, xs):qss) pa cea = do -- subsequent statements (zip'ed)
651 zipP <- dsLookupGlobalId zipPName
652 let pa' = mkLHsPatTup [pa, mkLHsVarPatTup xs]
653 ty'cea = parrElemType cea
654 res_expr = mkLHsVarTup xs
655 cqs <- dsPArrComp (map unLoc qs) res_expr undefined
656 let ty'cqs = parrElemType cqs
657 cea' = mkApps (Var zipP) [Type ty'cea, Type ty'cqs, cea, cqs]
658 parStmts qss pa' cea'
660 -- generate Core corresponding to `\p -> e'
662 deLambda :: Type -- type of the argument
663 -> LPat Id -- argument pattern
664 -> LHsExpr Id -- body
665 -> DsM (CoreExpr, Type)
667 mkLambda ty p =<< dsLExpr e
669 -- generate Core for a lambda pattern match, where the body is already in Core
671 mkLambda :: Type -- type of the argument
672 -> LPat Id -- argument pattern
673 -> CoreExpr -- desugared body
674 -> DsM (CoreExpr, Type)
675 mkLambda ty p ce = do
676 v <- newSysLocalDs ty
677 let errMsg = ptext (sLit "DsListComp.deLambda: internal error!")
679 cerr <- mkErrorAppDs pAT_ERROR_ID ce'ty errMsg
680 res <- matchSimply (Var v) (StmtCtxt PArrComp) p ce cerr
681 return (mkLams [v] res, ce'ty)
683 -- obtain the element type of the parallel array produced by the given Core
686 parrElemType :: CoreExpr -> Type
688 case splitTyConApp_maybe (exprType e) of
689 Just (tycon, [ty]) | tycon == parrTyCon -> ty
691 "DsListComp.parrElemType: not a parallel array type"