X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FdeSugar%2FDsListComp.lhs;h=63cae938d083cf5b061ccd87a272e3fc69999801;hp=166bfc244c54ec31ab5f0fa9fd7d444cf773c04d;hb=d76d9636aeebe933d160157331b8c8c0087e73ac;hpb=7fc01c4671980ea3c66d549c0ece4d82fd3f5ade diff --git a/compiler/deSugar/DsListComp.lhs b/compiler/deSugar/DsListComp.lhs index 166bfc2..63cae93 100644 --- a/compiler/deSugar/DsListComp.lhs +++ b/compiler/deSugar/DsListComp.lhs @@ -3,9 +3,10 @@ % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % -Desugaring list comprehensions and array comprehensions +Desugaring list comprehensions, monad comprehensions and array comprehensions \begin{code} +{-# LANGUAGE NamedFieldPuns #-} {-# OPTIONS -fno-warn-incomplete-patterns #-} -- The above warning supression flag is a temporary kludge. -- While working on this module you are encouraged to remove it and fix @@ -13,11 +14,11 @@ Desugaring list comprehensions and array comprehensions -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings -- for details -module DsListComp ( dsListComp, dsPArrComp ) where +module DsListComp ( dsListComp, dsPArrComp, dsMonadComp ) where #include "HsVersions.h" -import {-# SOURCE #-} DsExpr ( dsLExpr, dsLocalBinds ) +import {-# SOURCE #-} DsExpr ( dsExpr, dsLExpr, dsLocalBinds ) import HsSyn import TcHsSyn @@ -37,6 +38,7 @@ import PrelNames import SrcLoc import Outputable import FastString +import TcType \end{code} List comprehensions may be desugared in one of two ways: ``ordinary'' @@ -47,12 +49,14 @@ There will be at least one ``qualifier'' in the input. \begin{code} dsListComp :: [LStmt Id] - -> LHsExpr Id - -> Type -- Type of list elements + -> Type -- Type of entire list -> DsM CoreExpr -dsListComp lquals body elt_ty = do +dsListComp lquals res_ty = do dflags <- getDOptsDs let quals = map unLoc lquals + elt_ty = case tcTyConAppArgs res_ty of + [elt_ty] -> elt_ty + _ -> pprPanic "dsListComp" (ppr res_ty $$ ppr lquals) if not (dopt Opt_EnableRewriteRules dflags) || dopt Opt_IgnoreInterfacePragmas dflags -- Either rules are switched off, or we are ignoring what there are; @@ -60,8 +64,8 @@ dsListComp lquals body elt_ty = do -- Wadler-style desugaring || isParallelComp quals -- Foldr-style desugaring can't handle parallel list comprehensions - then deListComp quals body (mkNilExpr elt_ty) - else mkBuildExpr elt_ty (\(c, _) (n, _) -> dfListComp c n quals body) + then deListComp quals (mkNilExpr elt_ty) + else mkBuildExpr elt_ty (\(c, _) (n, _) -> dfListComp c n quals) -- Foldr/build should be enabled, so desugar -- into foldrs and builds @@ -72,32 +76,31 @@ dsListComp lquals body elt_ty = do -- 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 + 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 - +dsInnerListComp (stmts, bndrs) + = do { expr <- dsListComp (stmts ++ [noLoc $ mkLastStmt (mkBigLHsVarTup bndrs)]) + (mkListTy bndrs_tuple_type) + ; return (expr, bndrs_tuple_type) } + where + bndrs_tuple_type = mkBigCoreVarTupTy bndrs -- 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 +dsTransformStmt (TransformStmt stmts binders usingExpr maybeByExpr _ _) + = do { (expr, binders_tuple_type) <- dsInnerListComp (stmts, binders) + ; usingExpr' <- dsLExpr usingExpr - using_args <- - case maybeByExpr of + ; using_args <- + case maybeByExpr of Nothing -> return [expr] Just byExpr -> do byExpr' <- dsLExpr byExpr @@ -108,16 +111,16 @@ dsTransformStmt (TransformStmt stmts binders usingExpr maybeByExpr) = do 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) + ; let inner_list_expr = mkApps usingExpr' ((Type binders_tuple_type) : using_args) + 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 by using) = do +dsGroupStmt (GroupStmt { grpS_stmts = stmts, grpS_bndrs = binderMap + , grpS_by = by, grpS_using = using }) = do let (fromBinders, toBinders) = unzip binderMap fromBindersTypes = map idType fromBinders @@ -130,7 +133,7 @@ dsGroupStmt (GroupStmt stmts binderMap by using) = do -- 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' <- dsLExpr (either id noLoc using) + usingExpr' <- dsLExpr using usingArgs <- case by of Nothing -> return [expr] Just by_e -> do { by_e' <- dsLExpr by_e @@ -227,9 +230,40 @@ with the Unboxed variety. \begin{code} -deListComp :: [Stmt Id] -> LHsExpr Id -> CoreExpr -> DsM CoreExpr +deListComp :: [Stmt Id] -> CoreExpr -> DsM CoreExpr + +deListComp [] _ = panic "deListComp" + +deListComp (LastStmt body _ : quals) list + = -- Figure 7.4, SLPJ, p 135, rule C above + ASSERT( null quals ) + do { core_body <- dsLExpr body + ; return (mkConsExpr (exprType core_body) core_body list) } + + -- Non-last: must be a guard +deListComp (ExprStmt guard _ _ _ : quals) list = do -- rule B above + core_guard <- dsLExpr guard + core_rest <- deListComp quals list + return (mkIfThenElse core_guard core_rest list) + +-- [e | let B, qs] = let B in [e | qs] +deListComp (LetStmt binds : quals) list = do + core_rest <- deListComp quals list + dsLocalBinds binds core_rest + +deListComp (stmt@(TransformStmt {}) : quals) list = do + (inner_list_expr, pat) <- dsTransformStmt stmt + deBindComp pat inner_list_expr quals list + +deListComp (stmt@(GroupStmt {}) : quals) list = do + (inner_list_expr, pat) <- dsGroupStmt stmt + deBindComp pat inner_list_expr quals list + +deListComp (BindStmt pat list1 _ _ : quals) core_list2 = do -- rule A' above + core_list1 <- dsLExpr list1 + deBindComp pat core_list1 quals core_list2 -deListComp (ParStmt stmtss_w_bndrs : quals) body list +deListComp (ParStmt stmtss_w_bndrs _ _ _ : quals) list = do exps_and_qual_tys <- mapM dsInnerListComp stmtss_w_bndrs let (exps, qual_tys) = unzip exps_and_qual_tys @@ -238,7 +272,7 @@ deListComp (ParStmt stmtss_w_bndrs : quals) body list -- Deal with [e | pat <- zip l1 .. ln] in example above deBindComp pat (Let (Rec [(zip_fn, zip_rhs)]) (mkApps (Var zip_fn) exps)) - quals body list + quals list where bndrs_s = map snd stmtss_w_bndrs @@ -246,34 +280,6 @@ deListComp (ParStmt stmtss_w_bndrs : quals) body list -- pat is the pattern ((x1,..,xn), (y1,..,ym)) in the example above pat = mkBigLHsPatTup pats pats = map mkBigLHsVarPatTup bndrs_s - - -- Last: the one to return -deListComp [] body list = do -- Figure 7.4, SLPJ, p 135, rule C above - core_body <- dsLExpr body - return (mkConsExpr (exprType core_body) core_body list) - - -- Non-last: must be a guard -deListComp (ExprStmt guard _ _ : quals) body list = do -- rule B above - core_guard <- dsLExpr guard - core_rest <- deListComp quals body list - return (mkIfThenElse core_guard core_rest list) - --- [e | let B, qs] = let B in [e | qs] -deListComp (LetStmt binds : quals) body list = do - core_rest <- deListComp quals body list - 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 = do -- rule A' above - core_list1 <- dsLExpr list1 - deBindComp pat core_list1 quals body core_list2 \end{code} @@ -281,10 +287,9 @@ deListComp (BindStmt pat list1 _ _ : quals) body core_list2 = do -- rule A' abov deBindComp :: OutPat Id -> CoreExpr -> [Stmt Id] - -> LHsExpr Id -> CoreExpr -> DsM (Expr Id) -deBindComp pat core_list1 quals body core_list2 = do +deBindComp pat core_list1 quals core_list2 = do let u3_ty@u1_ty = exprType core_list1 -- two names, same thing @@ -301,7 +306,7 @@ deBindComp pat core_list1 quals body core_list2 = do core_fail = App (Var h) (Var u3) letrec_body = App (Var h) core_list1 - rest_expr <- deListComp quals body core_fail + rest_expr <- deListComp quals core_fail core_match <- matchSimply (Var u2) (StmtCtxt ListComp) pat rest_expr core_fail let @@ -336,48 +341,48 @@ TE[ e | p <- l , q ] c n = let \begin{code} 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 = do - core_body <- dsLExpr body - return (mkApps (Var c_id) [core_body, Var n_id]) +dfListComp _ _ [] = panic "dfListComp" + +dfListComp c_id n_id (LastStmt body _ : quals) + = ASSERT( null quals ) + do { core_body <- dsLExpr body + ; return (mkApps (Var c_id) [core_body, Var n_id]) } -- Non-last: must be a guard -dfListComp c_id n_id (ExprStmt guard _ _ : quals) body = do +dfListComp c_id n_id (ExprStmt guard _ _ _ : quals) = do core_guard <- dsLExpr guard - core_rest <- dfListComp c_id n_id quals body + core_rest <- dfListComp c_id n_id quals return (mkIfThenElse core_guard core_rest (Var n_id)) -dfListComp c_id n_id (LetStmt binds : quals) body = do +dfListComp c_id n_id (LetStmt binds : quals) = do -- new in 1.3, local bindings - core_rest <- dfListComp c_id n_id quals body + core_rest <- dfListComp c_id n_id quals dsLocalBinds binds core_rest -dfListComp c_id n_id (stmt@(TransformStmt {}) : quals) body = do +dfListComp c_id n_id (stmt@(TransformStmt {}) : quals) = 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 + dfBindComp c_id n_id (pat, inner_list_expr) quals -dfListComp c_id n_id (stmt@(GroupStmt {}) : quals) body = do +dfListComp c_id n_id (stmt@(GroupStmt {}) : quals) = 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 + dfBindComp c_id n_id (pat, inner_list_expr) quals -dfListComp c_id n_id (BindStmt pat list1 _ _ : quals) body = do +dfListComp c_id n_id (BindStmt pat list1 _ _ : quals) = do -- evaluate the two lists 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 c_id n_id (pat, core_list1) quals 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 +dfBindComp c_id n_id (pat, core_list1) quals = do -- find the required type let x_ty = hsLPatType pat b_ty = idType n_id @@ -386,7 +391,7 @@ dfBindComp c_id n_id (pat, core_list1) quals body = do [b, x] <- newSysLocalsDs [b_ty, x_ty] -- build rest of the comprehesion - core_rest <- dfListComp c_id b quals body + core_rest <- dfListComp c_id b quals -- build the pattern match core_expr <- matchSimply (Var x) (StmtCtxt ListComp) @@ -481,9 +486,6 @@ mkUnzipBind elt_tys = do 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} %************************************************************************ @@ -499,11 +501,10 @@ mkUnzipBind elt_tys = do -- [:e | qss:] = <<[:e | qss:]>> () [:():] -- dsPArrComp :: [Stmt Id] - -> LHsExpr Id - -> Type -- Don't use; called with `undefined' below -> DsM CoreExpr -dsPArrComp [ParStmt qss] body _ = -- parallel comprehension - dePArrParComp qss body + +-- Special case for parallel comprehension +dsPArrComp (ParStmt qss _ _ _ : quals) = dePArrParComp qss quals -- Special case for simple generators: -- @@ -514,8 +515,8 @@ dsPArrComp [ParStmt qss] body _ = -- parallel comprehension -- <<[:e' | p <- e, qs:]>> = -- <<[:e' | qs:]>> p (filterP (\x -> case x of {p -> True; _ -> False}) e) -- -dsPArrComp (BindStmt p e _ _ : qs) body _ = do - filterP <- dsLookupGlobalId filterPName +dsPArrComp (BindStmt p e _ _ : qs) = do + filterP <- dsLookupDPHId filterPName ce <- dsLExpr e let ety'ce = parrElemType ce false = Var falseDataConId @@ -524,38 +525,41 @@ dsPArrComp (BindStmt p e _ _ : qs) body _ = do pred <- matchSimply (Var v) (StmtCtxt PArrComp) p true false let gen | isIrrefutableHsPat p = ce | otherwise = mkApps (Var filterP) [Type ety'ce, mkLams [v] pred, ce] - dePArrComp qs body p gen + dePArrComp qs p gen -dsPArrComp qs body _ = do -- no ParStmt in `qs' - sglP <- dsLookupGlobalId singletonPName +dsPArrComp qs = do -- no ParStmt in `qs' + sglP <- dsLookupDPHId singletonPName let unitArray = mkApps (Var sglP) [Type unitTy, mkCoreTup []] - dePArrComp qs body (noLoc $ WildPat unitTy) unitArray + dePArrComp qs (noLoc $ WildPat unitTy) unitArray -- the work horse -- dePArrComp :: [Stmt Id] - -> LHsExpr Id -> LPat Id -- the current generator pattern -> CoreExpr -- the current generator expression -> DsM CoreExpr + +dePArrComp [] _ _ = panic "dePArrComp" + -- -- <<[:e' | :]>> pa ea = mapP (\pa -> e') ea -- -dePArrComp [] e' pa cea = do - mapP <- dsLookupGlobalId mapPName - let ty = parrElemType cea - (clam, ty'e') <- deLambda ty pa e' - return $ mkApps (Var mapP) [Type ty, Type ty'e', clam, cea] +dePArrComp (LastStmt e' _ : quals) pa cea + = ASSERT( null quals ) + do { mapP <- dsLookupDPHId mapPName + ; let ty = parrElemType cea + ; (clam, ty'e') <- deLambda ty pa e' + ; return $ mkApps (Var mapP) [Type ty, Type ty'e', clam, cea] } -- -- <<[:e' | b, qs:]>> pa ea = <<[:e' | qs:]>> pa (filterP (\pa -> b) ea) -- -dePArrComp (ExprStmt b _ _ : qs) body pa cea = do - filterP <- dsLookupGlobalId filterPName +dePArrComp (ExprStmt b _ _ _ : qs) pa cea = do + filterP <- dsLookupDPHId filterPName let ty = parrElemType cea (clam,_) <- deLambda ty pa b - dePArrComp qs body pa (mkApps (Var filterP) [Type ty, clam, cea]) + dePArrComp qs pa (mkApps (Var filterP) [Type ty, clam, cea]) -- -- <<[:e' | p <- e, qs:]>> pa ea = @@ -570,9 +574,9 @@ dePArrComp (ExprStmt b _ _ : qs) body pa cea = do -- in -- <<[:e' | qs:]>> (pa, p) (crossMapP ea ef) -- -dePArrComp (BindStmt p e _ _ : qs) body pa cea = do - filterP <- dsLookupGlobalId filterPName - crossMapP <- dsLookupGlobalId crossMapPName +dePArrComp (BindStmt p e _ _ : qs) pa cea = do + filterP <- dsLookupDPHId filterPName + crossMapP <- dsLookupDPHId crossMapPName ce <- dsLExpr e let ety'cea = parrElemType cea ety'ce = parrElemType ce @@ -586,7 +590,7 @@ dePArrComp (BindStmt p e _ _ : qs) body pa cea = do let ety'cef = ety'ce -- filter doesn't change the element type pa' = mkLHsPatTup [pa, p] - dePArrComp qs body pa' (mkApps (Var crossMapP) + dePArrComp qs pa' (mkApps (Var crossMapP) [Type ety'cea, Type ety'cef, cea, clam]) -- -- <<[:e' | let ds, qs:]>> pa ea = @@ -595,8 +599,8 @@ dePArrComp (BindStmt p e _ _ : qs) body pa cea = do -- where -- {x_1, ..., x_n} = DV (ds) -- Defined Variables -- -dePArrComp (LetStmt ds : qs) body pa cea = do - mapP <- dsLookupGlobalId mapPName +dePArrComp (LetStmt ds : qs) pa cea = do + mapP <- dsLookupDPHId mapPName let xs = collectLocalBinders ds ty'cea = parrElemType cea v <- newSysLocalDs ty'cea @@ -610,14 +614,14 @@ dePArrComp (LetStmt ds : qs) body pa cea = do ccase <- matchSimply (Var v) (StmtCtxt PArrComp) pa projBody cerr let pa' = mkLHsPatTup [pa, mkLHsPatTup (map nlVarPat xs)] proj = mkLams [v] ccase - dePArrComp qs body pa' (mkApps (Var mapP) + dePArrComp qs pa' (mkApps (Var mapP) [Type ty'cea, Type errTy, proj, cea]) -- -- The parser guarantees that parallel comprehensions can only appear as -- singeltons qualifier lists, which we already special case in the caller. -- So, encountering one here is a bug. -- -dePArrComp (ParStmt _ : _) _ _ _ = +dePArrComp (ParStmt _ _ _ _ : _) _ _ = panic "DsListComp.dePArrComp: malformed comprehension AST" -- <<[:e' | qs | qss:]>> pa ea = @@ -626,26 +630,26 @@ dePArrComp (ParStmt _ : _) _ _ _ = -- where -- {x_1, ..., x_n} = DV (qs) -- -dePArrParComp :: [([LStmt Id], [Id])] -> LHsExpr Id -> DsM CoreExpr -dePArrParComp qss body = do +dePArrParComp :: [([LStmt Id], [Id])] -> [Stmt Id] -> DsM CoreExpr +dePArrParComp qss quals = do (pQss, ceQss) <- deParStmt qss - dePArrComp [] body pQss ceQss + dePArrComp quals pQss ceQss where deParStmt [] = -- empty parallel statement lists have no source representation panic "DsListComp.dePArrComp: Empty parallel list comprehension" deParStmt ((qs, xs):qss) = do -- first statement let res_expr = mkLHsVarTuple xs - cqs <- dsPArrComp (map unLoc qs) res_expr undefined + cqs <- dsPArrComp (map unLoc qs ++ [mkLastStmt res_expr]) parStmts qss (mkLHsVarPatTup xs) cqs --- parStmts [] pa cea = return (pa, cea) parStmts ((qs, xs):qss) pa cea = do -- subsequent statements (zip'ed) - zipP <- dsLookupGlobalId zipPName + zipP <- dsLookupDPHId zipPName let pa' = mkLHsPatTup [pa, mkLHsVarPatTup xs] ty'cea = parrElemType cea res_expr = mkLHsVarTuple xs - cqs <- dsPArrComp (map unLoc qs) res_expr undefined + cqs <- dsPArrComp (map unLoc qs ++ [mkLastStmt res_expr]) let ty'cqs = parrElemType cqs cea' = mkApps (Var zipP) [Type ty'cea, Type ty'cqs, cea, cqs] parStmts qss pa' cea' @@ -683,3 +687,242 @@ parrElemType e = _ -> panic "DsListComp.parrElemType: not a parallel array type" \end{code} + +Translation for monad comprehensions + +\begin{code} +-- Entry point for monad comprehension desugaring +dsMonadComp :: [LStmt Id] -> DsM CoreExpr +dsMonadComp stmts = dsMcStmts stmts + +dsMcStmts :: [LStmt Id] -> DsM CoreExpr +dsMcStmts [] = panic "dsMcStmts" +dsMcStmts (L loc stmt : lstmts) = putSrcSpanDs loc (dsMcStmt stmt lstmts) + +--------------- +dsMcStmt :: Stmt Id -> [LStmt Id] -> DsM CoreExpr + +dsMcStmt (LastStmt body ret_op) stmts + = ASSERT( null stmts ) + do { body' <- dsLExpr body + ; ret_op' <- dsExpr ret_op + ; return (App ret_op' body') } + +-- [ .. | let binds, stmts ] +dsMcStmt (LetStmt binds) stmts + = do { rest <- dsMcStmts stmts + ; dsLocalBinds binds rest } + +-- [ .. | a <- m, stmts ] +dsMcStmt (BindStmt pat rhs bind_op fail_op) stmts + = do { rhs' <- dsLExpr rhs + ; dsMcBindStmt pat rhs' bind_op fail_op stmts } + +-- Apply `guard` to the `exp` expression +-- +-- [ .. | exp, stmts ] +-- +dsMcStmt (ExprStmt exp then_exp guard_exp _) stmts + = do { exp' <- dsLExpr exp + ; guard_exp' <- dsExpr guard_exp + ; then_exp' <- dsExpr then_exp + ; rest <- dsMcStmts stmts + ; return $ mkApps then_exp' [ mkApps guard_exp' [exp'] + , rest ] } + +-- Transform statements desugar like this: +-- +-- [ .. | qs, then f by e ] -> f (\q_v -> e) [| qs |] +-- +-- where [| qs |] is the desugared inner monad comprehenion generated by the +-- statements `qs`. +dsMcStmt (TransformStmt stmts binders usingExpr maybeByExpr return_op bind_op) stmts_rest + = do { expr <- dsInnerMonadComp stmts binders return_op + ; let binders_tup_type = mkBigCoreTupTy $ map idType binders + ; usingExpr' <- dsLExpr usingExpr + ; using_args <- case maybeByExpr of + Nothing -> return [expr] + Just byExpr -> do + byExpr' <- dsLExpr byExpr + us <- newUniqueSupply + tup_binder <- newSysLocalDs binders_tup_type + let byExprWrapper = mkTupleCase us binders byExpr' tup_binder (Var tup_binder) + return [Lam tup_binder byExprWrapper, expr] + + ; let pat = mkBigLHsVarPatTup binders + rhs = mkApps usingExpr' ((Type binders_tup_type) : using_args) + + ; dsMcBindStmt pat rhs bind_op noSyntaxExpr stmts_rest } + +-- Group statements desugar like this: +-- +-- [| (q, then group by e using f); rest |] +-- ---> f {qt} (\qv -> e) [| q; return qv |] >>= \ n_tup -> +-- case unzip n_tup of qv' -> [| rest |] +-- +-- where variables (v1:t1, ..., vk:tk) are bound by q +-- qv = (v1, ..., vk) +-- qt = (t1, ..., tk) +-- (>>=) :: m2 a -> (a -> m3 b) -> m3 b +-- f :: forall a. (a -> t) -> m1 a -> m2 (n a) +-- n_tup :: n qt +-- unzip :: n qt -> (n t1, ..., n tk) (needs Functor n) + +dsMcStmt (GroupStmt { grpS_stmts = stmts, grpS_bndrs = bndrs + , grpS_by = by, grpS_using = using + , grpS_ret = return_op, grpS_bind = bind_op + , grpS_fmap = fmap_op }) stmts_rest + = do { let (from_bndrs, to_bndrs) = unzip bndrs + from_bndr_tys = map idType from_bndrs -- Types ty + + -- Desugar an inner comprehension which outputs a list of tuples of the "from" binders + ; expr <- dsInnerMonadComp stmts from_bndrs return_op + + -- 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' <- dsLExpr using + ; usingArgs <- case by of + Nothing -> return [expr] + Just by_e -> do { by_e' <- dsLExpr by_e + ; lam <- matchTuple from_bndrs by_e' + ; return [lam, expr] } + + -- Generate the expressions to build the grouped list + -- Build a pattern that ensures the consumer binds into the NEW binders, + -- which hold monads rather than single values + ; fmap_op' <- dsExpr fmap_op + ; bind_op' <- dsExpr bind_op + ; let bind_ty = exprType bind_op' -- m2 (n (a,b,c)) -> (n (a,b,c) -> r1) -> r2 + n_tup_ty = funArgTy $ funArgTy $ funResultTy bind_ty -- n (a,b,c) + tup_n_ty = mkBigCoreVarTupTy to_bndrs + + ; body <- dsMcStmts stmts_rest + ; n_tup_var <- newSysLocalDs n_tup_ty + ; tup_n_var <- newSysLocalDs tup_n_ty + ; tup_n_expr <- mkMcUnzipM fmap_op' n_tup_var from_bndr_tys + ; us <- newUniqueSupply + ; let rhs' = mkApps usingExpr' usingArgs + body' = mkTupleCase us to_bndrs body tup_n_var tup_n_expr + + ; return (mkApps bind_op' [rhs', Lam n_tup_var body']) } + +-- Parallel statements. Use `Control.Monad.Zip.mzip` to zip parallel +-- statements, for example: +-- +-- [ body | qs1 | qs2 | qs3 ] +-- -> [ body | (bndrs1, (bndrs2, bndrs3)) +-- <- [bndrs1 | qs1] `mzip` ([bndrs2 | qs2] `mzip` [bndrs3 | qs3]) ] +-- +-- where `mzip` has type +-- mzip :: forall a b. m a -> m b -> m (a,b) +-- NB: we need a polymorphic mzip because we call it several times + +dsMcStmt (ParStmt pairs mzip_op bind_op return_op) stmts_rest + = do { exps_w_tys <- mapM ds_inner pairs -- Pairs (exp :: m ty, ty) + ; mzip_op' <- dsExpr mzip_op + + ; let -- The pattern variables + pats = map (mkBigLHsVarPatTup . snd) pairs + -- Pattern with tuples of variables + -- [v1,v2,v3] => (v1, (v2, v3)) + pat = foldr1 (\p1 p2 -> mkLHsPatTup [p1, p2]) pats + (rhs, _) = foldr1 (\(e1,t1) (e2,t2) -> + (mkApps mzip_op' [Type t1, Type t2, e1, e2], + mkBoxedTupleTy [t1,t2])) + exps_w_tys + + ; dsMcBindStmt pat rhs bind_op noSyntaxExpr stmts_rest } + where + ds_inner (stmts, bndrs) = do { exp <- dsInnerMonadComp stmts bndrs mono_ret_op + ; return (exp, tup_ty) } + where + mono_ret_op = HsWrap (WpTyApp tup_ty) return_op + tup_ty = mkBigCoreVarTupTy bndrs + +dsMcStmt stmt _ = pprPanic "dsMcStmt: unexpected stmt" (ppr stmt) + + +matchTuple :: [Id] -> CoreExpr -> DsM CoreExpr +-- (matchTuple [a,b,c] body) +-- returns the Core term +-- \x. case x of (a,b,c) -> body +matchTuple ids body + = do { us <- newUniqueSupply + ; tup_id <- newSysLocalDs (mkBigCoreVarTupTy ids) + ; return (Lam tup_id $ mkTupleCase us ids body tup_id (Var tup_id)) } + +-- general `rhs' >>= \pat -> stmts` desugaring where `rhs'` is already a +-- desugared `CoreExpr` +dsMcBindStmt :: LPat Id + -> CoreExpr -- ^ the desugared rhs of the bind statement + -> SyntaxExpr Id + -> SyntaxExpr Id + -> [LStmt Id] + -> DsM CoreExpr +dsMcBindStmt pat rhs' bind_op fail_op stmts + = do { body <- dsMcStmts stmts + ; bind_op' <- dsExpr bind_op + ; var <- selectSimpleMatchVarL pat + ; let bind_ty = exprType bind_op' -- rhs -> (pat -> res1) -> res2 + res1_ty = funResultTy (funArgTy (funResultTy bind_ty)) + ; match <- matchSinglePat (Var var) (StmtCtxt DoExpr) pat + res1_ty (cantFailMatchResult body) + ; match_code <- handle_failure pat match fail_op + ; return (mkApps bind_op' [rhs', Lam var match_code]) } + + where + -- In a monad comprehension expression, pattern-match failure just calls + -- the monadic `fail` rather than throwing an exception + handle_failure pat match fail_op + | matchCanFail match + = do { fail_op' <- dsExpr fail_op + ; fail_msg <- mkStringExpr (mk_fail_msg pat) + ; extractMatchResult match (App fail_op' fail_msg) } + | otherwise + = extractMatchResult match (error "It can't fail") + + mk_fail_msg :: Located e -> String + mk_fail_msg pat = "Pattern match failure in monad comprehension at " ++ + showSDoc (ppr (getLoc pat)) + +-- Desugar nested monad comprehensions, for example in `then..` constructs +-- dsInnerMonadComp quals [a,b,c] ret_op +-- returns the desugaring of +-- [ (a,b,c) | quals ] + +dsInnerMonadComp :: [LStmt Id] + -> [Id] -- Return a tuple of these variables + -> HsExpr Id -- The monomorphic "return" operator + -> DsM CoreExpr +dsInnerMonadComp stmts bndrs ret_op + = dsMcStmts (stmts ++ [noLoc (LastStmt (mkBigLHsVarTup bndrs) ret_op)]) + +-- The `unzip` function for `GroupStmt` in a monad comprehensions +-- +-- unzip :: m (a,b,..) -> (m a,m b,..) +-- unzip m_tuple = ( liftM selN1 m_tuple +-- , liftM selN2 m_tuple +-- , .. ) +-- +-- mkMcUnzipM fmap ys [t1, t2] +-- = ( fmap (selN1 :: (t1, t2) -> t1) ys +-- , fmap (selN2 :: (t1, t2) -> t2) ys ) + +mkMcUnzipM :: CoreExpr -- fmap + -> Id -- Of type n (a,b,c) + -> [Type] -- [a,b,c] + -> DsM CoreExpr -- Of type (n a, n b, n c) +mkMcUnzipM fmap_op ys elt_tys + = do { xs <- mapM newSysLocalDs elt_tys + ; tup_xs <- newSysLocalDs (mkBigCoreTupTy elt_tys) + + ; let arg_ty = idType ys + mk_elt i = mkApps fmap_op -- fmap :: forall a b. (a -> b) -> n a -> n b + [ Type arg_ty, Type (elt_tys !! i) + , mk_sel i, Var ys] + + mk_sel n = Lam tup_xs $ + mkTupleSelector xs (xs !! n) tup_xs (Var tup_xs) + + ; return (mkBigCoreTup (map mk_elt [0..length elt_tys - 1])) } +\end{code}