%
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
-\section[DsListComp]{Desugaring list comprehensions}
+\section[DsListComp]{Desugaring list comprehensions and array comprehensions}
\begin{code}
-module DsListComp ( dsListComp ) where
+module DsListComp ( dsListComp, dsPArrComp ) where
#include "HsVersions.h"
-import {-# SOURCE #-} DsExpr ( dsExpr, dsLet )
+import {-# SOURCE #-} DsExpr ( dsLExpr, dsLet )
-import HsSyn ( Stmt(..), HsExpr )
-import TcHsSyn ( TypecheckedStmt, TypecheckedHsExpr )
-import DsHsSyn ( outPatType )
+import BasicTypes ( Boxity(..) )
+import HsSyn
+import TcHsSyn ( hsPatType )
import CoreSyn
import DsMonad -- the monadery used in the desugarer
import DsUtils
-import CmdLineOpts ( opt_FoldrBuildOn )
-import CoreUtils ( exprType )
+import CmdLineOpts ( DynFlag(..), dopt, opt_RulesOff )
+import CoreUtils ( exprType, mkIfThenElse )
import Id ( idType )
-import Var ( Id, TyVar )
-import PrelInfo ( foldrId, buildId )
-import Type ( mkTyVarTy, mkForAllTy, mkFunTys, mkFunTy, Type )
-import TysPrim ( alphaTyVar, alphaTy )
-import TysWiredIn ( nilDataCon, consDataCon, listTyCon )
+import Var ( Id )
+import Type ( mkTyVarTy, mkFunTys, mkFunTy, Type,
+ splitTyConApp_maybe )
+import TysPrim ( alphaTyVar )
+import TysWiredIn ( nilDataCon, consDataCon, trueDataConId, falseDataConId,
+ unitDataConId, unitTy, mkListTy, parrTyCon )
import Match ( matchSimply )
-import Outputable
+import PrelNames ( foldrName, buildName, replicatePName, mapPName,
+ filterPName, zipPName, crossPName )
+import PrelInfo ( pAT_ERROR_ID )
+import SrcLoc ( noLoc, unLoc )
+import Panic ( panic )
\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 :: [TypecheckedStmt]
+dsListComp :: [LStmt Id]
-> Type -- Type of list elements
-> DsM CoreExpr
-
-dsListComp quals elt_ty
- | not opt_FoldrBuildOn -- Be boring
- = deListComp quals (mkNilExpr elt_ty)
-
- | otherwise -- foldr/build lives!
- = newTyVarsDs [alphaTyVar] `thenDs` \ [n_tyvar] ->
+dsListComp lquals 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 (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 `thenDs` \ result ->
-
- returnDs (Var buildId `App` Type elt_ty
- `App` mkLams [n_tyvar, c, n] result)
+ newSysLocalsDs [c_ty,n_ty] `thenDs` \ [c, n] ->
+ dfListComp c n quals `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
\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 ParStmt 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 :: [Stmt Id] -> CoreExpr -> DsM CoreExpr
+
+deListComp (ParStmt stmtss_w_bndrs : quals) list
+ = mappM do_list_comp stmtss_w_bndrs `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
+ bndrs_s = map snd stmtss_w_bndrs
+
+ -- pat is the pattern ((x1,..,xn), (y1,..,ym)) in the example above
+ pat = noLoc (TuplePat pats Boxed)
+ pats = map mk_hs_tuple_pat bndrs_s
+
+ -- Types of (x1,..,xn), (y1,..,yn) etc
+ qual_tys = map mk_bndrs_tys bndrs_s
-deListComp [ReturnStmt expr] list -- Figure 7.4, SLPJ, p 135, rule C above
- = dsExpr expr `thenDs` \ core_expr ->
+ do_list_comp (stmts, bndrs)
+ = dsListComp (stmts ++ [noLoc $ ResultStmt (mk_hs_tuple_expr bndrs)])
+ (mk_bndrs_tys bndrs)
+
+ mk_bndrs_tys bndrs = mkCoreTupTy (map idType bndrs)
+
+ -- Last: the one to return
+deListComp [ResultStmt expr] list -- Figure 7.4, SLPJ, p 135, rule C above
+ = dsLExpr expr `thenDs` \ core_expr ->
returnDs (mkConsExpr (exprType core_expr) core_expr list)
-deListComp (GuardStmt guard locn : quals) list -- rule B above
- = dsExpr guard `thenDs` \ core_guard ->
+ -- Non-last: must be a guard
+deListComp (ExprStmt guard ty : quals) list -- rule B above
+ = dsLExpr guard `thenDs` \ core_guard ->
deListComp quals list `thenDs` \ core_rest ->
returnDs (mkIfThenElse core_guard core_rest 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 ->
- let
+deListComp (BindStmt pat list1 : quals) core_list2 -- rule A' above
+ = dsLExpr list1 `thenDs` \ core_list1 ->
+ 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
- u2_ty = outPatType pat
+ u2_ty = hsPatType pat
res_ty = exprType core_list2
h_ty = u1_ty `mkFunTy` res_ty
letrec_body = App (Var h) core_list1
in
deListComp quals core_fail `thenDs` \ rest_expr ->
- matchSimply (Var u2) ListCompMatch pat
+ matchSimply (Var u2) (StmtCtxt 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
+ = 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
+ 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 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 [b] = nlVarPat b
+mk_hs_tuple_pat bs = noLoc $ TuplePat (map nlVarPat bs) Boxed
+\end{code}
+
+
%************************************************************************
%* *
\subsection[DsListComp-foldr-build]{Foldr/Build desugaring of list comprehensions}
\begin{code}
dfListComp :: Id -> Id -- 'c' and 'n'
- -> [TypecheckedStmt] -- the rest of the qual's
+ -> [Stmt Id] -- the rest of the qual's
-> DsM CoreExpr
-dfListComp c_id n_id [ReturnStmt expr]
- = dsExpr expr `thenDs` \ core_expr ->
+ -- Last: the one to return
+dfListComp c_id n_id [ResultStmt expr]
+ = dsLExpr expr `thenDs` \ core_expr ->
returnDs (mkApps (Var c_id) [core_expr, Var n_id])
-dfListComp c_id n_id (GuardStmt guard locn : quals)
- = dsExpr guard `thenDs` \ core_guard ->
+ -- Non-last: must be a guard
+dfListComp c_id n_id (ExprStmt guard ty : quals)
+ = dsLExpr 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 quals `thenDs` \ core_rest ->
dsLet binds core_rest
-dfListComp c_id n_id (BindStmt pat list1 locn : quals)
+dfListComp c_id n_id (BindStmt pat list1 : quals)
-- evaluate the two lists
- = dsExpr list1 `thenDs` \ core_list1 ->
+ = dsLExpr list1 `thenDs` \ core_list1 ->
-- find the required type
- let x_ty = outPatType pat
+ let x_ty = hsPatType pat
b_ty = idType n_id
in
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) (StmtCtxt ListComp)
+ pat core_rest (Var b) `thenDs` \ core_expr ->
-- now build the outermost foldr, and return
+ dsLookupGlobalId foldrName `thenDs` \ foldr_id ->
returnDs (
- Var foldrId `App` Type x_ty
- `App` Type b_ty
- `App` mkLams [x, b] core_expr
- `App` Var n_id
- `App` core_list1
+ 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[DsPArrComp]{Desugaring of array comprehensions}
+%* *
+%************************************************************************
+\begin{code}
+
+-- entry point for desugaring a parallel array comprehension
+--
+-- [:e | qss:] = <<[:e | qss:]>> () [:():]
+--
+dsPArrComp :: [Stmt Id]
+ -> Type -- Don't use; called with `undefined' below
+ -> DsM CoreExpr
+dsPArrComp qs _ =
+ dsLookupGlobalId replicatePName `thenDs` \repP ->
+ let unitArray = mkApps (Var repP) [Type unitTy,
+ mkIntExpr 1,
+ mkCoreTup []]
+ in
+ dePArrComp qs (noLoc (TuplePat [] Boxed)) unitArray
+
+-- the work horse
+--
+dePArrComp :: [Stmt Id]
+ -> LPat Id -- the current generator pattern
+ -> CoreExpr -- the current generator expression
+ -> DsM CoreExpr
+--
+-- <<[:e' | :]>> pa ea = mapP (\pa -> e') ea
+--
+dePArrComp [ResultStmt e'] pa cea =
+ dsLookupGlobalId mapPName `thenDs` \mapP ->
+ let ty = parrElemType cea
+ in
+ deLambda ty pa e' `thenDs` \(clam,
+ ty'e') ->
+ returnDs $ 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) pa cea =
+ dsLookupGlobalId filterPName `thenDs` \filterP ->
+ let ty = parrElemType cea
+ in
+ deLambda ty pa b `thenDs` \(clam,_) ->
+ dePArrComp qs pa (mkApps (Var filterP) [Type ty, clam, cea])
+--
+-- <<[:e' | p <- e, qs:]>> pa ea =
+-- let ef = filterP (\x -> case x of {p -> True; _ -> False}) e
+-- in
+-- <<[:e' | qs:]>> (pa, p) (crossP ea ef)
+--
+dePArrComp (BindStmt p e : qs) pa cea =
+ dsLookupGlobalId filterPName `thenDs` \filterP ->
+ dsLookupGlobalId crossPName `thenDs` \crossP ->
+ dsLExpr e `thenDs` \ce ->
+ let ty'cea = parrElemType cea
+ ty'ce = parrElemType ce
+ false = Var falseDataConId
+ true = Var trueDataConId
+ in
+ newSysLocalDs ty'ce `thenDs` \v ->
+ matchSimply (Var v) (StmtCtxt PArrComp) p true false `thenDs` \pred ->
+ let cef = mkApps (Var filterP) [Type ty'ce, mkLams [v] pred, ce]
+ ty'cef = ty'ce -- filterP preserves the type
+ pa' = noLoc (TuplePat [pa, p] Boxed)
+ in
+ dePArrComp qs pa' (mkApps (Var crossP) [Type ty'cea, Type ty'cef, cea, cef])
+--
+-- <<[:e' | let ds, qs:]>> pa ea =
+-- <<[:e' | qs:]>> (pa, (x_1, ..., x_n))
+-- (mapP (\v@pa -> (v, let ds in (x_1, ..., x_n))) ea)
+-- where
+-- {x_1, ..., x_n} = DV (ds) -- Defined Variables
+--
+dePArrComp (LetStmt ds : qs) pa cea =
+ dsLookupGlobalId mapPName `thenDs` \mapP ->
+ let xs = map unLoc (collectGroupBinders ds)
+ ty'cea = parrElemType cea
+ in
+ newSysLocalDs ty'cea `thenDs` \v ->
+ dsLet ds (mkCoreTup (map Var xs)) `thenDs` \clet ->
+ newSysLocalDs (exprType clet) `thenDs` \let'v ->
+ let projBody = mkDsLet (NonRec let'v clet) $
+ mkCoreTup [Var v, Var let'v]
+ errTy = exprType projBody
+ errMsg = "DsListComp.dePArrComp: internal error!"
+ in
+ mkErrorAppDs pAT_ERROR_ID errTy errMsg `thenDs` \cerr ->
+ matchSimply (Var v) (StmtCtxt PArrComp) pa projBody cerr `thenDs` \ccase ->
+ let pa' = noLoc $ TuplePat [pa, noLoc (TuplePat (map nlVarPat xs) Boxed)] Boxed
+ proj = mkLams [v] ccase
+ in
+ dePArrComp qs pa' (mkApps (Var mapP) [Type ty'cea, proj, cea])
+--
+-- <<[:e' | qs | qss:]>> pa ea =
+-- <<[:e' | qss:]>> (pa, (x_1, ..., x_n))
+-- (zipP ea <<[:(x_1, ..., x_n) | qs:]>>)
+-- where
+-- {x_1, ..., x_n} = DV (qs)
+--
+dePArrComp (ParStmt [] : qss2) pa cea = dePArrComp qss2 pa cea
+dePArrComp (ParStmt ((qs, xs):qss) : qss2) pa cea =
+ dsLookupGlobalId zipPName `thenDs` \zipP ->
+ let pa' = noLoc $ TuplePat [pa, noLoc (TuplePat (map nlVarPat xs) Boxed)] Boxed
+ ty'cea = parrElemType cea
+ resStmt = ResultStmt (noLoc $ ExplicitTuple (map nlHsVar xs) Boxed)
+ in
+ dsPArrComp (map unLoc qs ++ [resStmt]) undefined `thenDs` \cqs ->
+ let ty'cqs = parrElemType cqs
+ cea' = mkApps (Var zipP) [Type ty'cea, Type ty'cqs, cea, cqs]
+ in
+ dePArrComp (ParStmt qss : qss2) pa' cea'
+
+-- generate Core corresponding to `\p -> e'
+--
+deLambda :: Type -- type of the argument
+ -> LPat Id -- argument pattern
+ -> LHsExpr Id -- body
+ -> DsM (CoreExpr, Type)
+deLambda ty p e =
+ newSysLocalDs ty `thenDs` \v ->
+ dsLExpr e `thenDs` \ce ->
+ let errTy = exprType ce
+ errMsg = "DsListComp.deLambda: internal error!"
+ in
+ mkErrorAppDs pAT_ERROR_ID errTy errMsg `thenDs` \cerr ->
+ matchSimply (Var v) (StmtCtxt PArrComp) p ce cerr `thenDs` \res ->
+ returnDs (mkLams [v] res, errTy)
+
+-- obtain the element type of the parallel array produced by the given Core
+-- expression
+--
+parrElemType :: CoreExpr -> Type
+parrElemType e =
+ case splitTyConApp_maybe (exprType e) of
+ Just (tycon, [ty]) | tycon == parrTyCon -> ty
+ _ -> panic
+ "DsListComp.parrElemType: not a parallel array type"
+\end{code}
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