+++ /dev/null
-%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
-%
-\section[DsListComp]{Desugaring list comprehensions and array comprehensions}
-
-\begin{code}
-module DsListComp ( dsListComp, dsPArrComp ) where
-
-#include "HsVersions.h"
-
-import {-# SOURCE #-} DsExpr ( dsLExpr, dsLocalBinds )
-
-import BasicTypes ( Boxity(..) )
-import HsSyn
-import TcHsSyn ( hsPatType, mkVanillaTuplePat )
-import CoreSyn
-
-import DsMonad -- the monadery used in the desugarer
-import DsUtils
-
-import DynFlags ( DynFlag(..), dopt )
-import StaticFlags ( opt_RulesOff )
-import CoreUtils ( exprType, mkIfThenElse )
-import Id ( idType )
-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 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''
-(as you would expect if you read SLPJ's book) and ``with foldr/build
-turned on'' (if you read Gill {\em et al.}'s paper on the subject).
-
-There will be at least one ``qualifier'' in the input.
-
-\begin{code}
-dsListComp :: [LStmt Id]
- -> 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
-\end{code}
-
-%************************************************************************
-%* *
-\subsection[DsListComp-ordinary]{Ordinary desugaring of list comprehensions}
-%* *
-%************************************************************************
-
-Just as in Phil's chapter~7 in SLPJ, using the rules for
-optimally-compiled list comprehensions. This is what Kevin followed
-as well, and I quite happily do the same. The TQ translation scheme
-transforms a list of qualifiers (either boolean expressions or
-generators) into a single expression which implements the list
-comprehension. Because we are generating 2nd-order polymorphic
-lambda-calculus, calls to NIL and CONS must be applied to a type
-argument, as well as their usual value arguments.
-\begin{verbatim}
-TE << [ e | qs ] >> = TQ << [ e | qs ] ++ Nil (typeOf e) >>
-
-(Rule C)
-TQ << [ e | ] ++ L >> = Cons (typeOf e) TE <<e>> TE <<L>>
-
-(Rule B)
-TQ << [ e | b , qs ] ++ L >> =
- if TE << b >> then TQ << [ e | qs ] ++ L >> else TE << L >>
-
-(Rule A')
-TQ << [ e | p <- L1, qs ] ++ L2 >> =
- letrec
- h = \ u1 ->
- case u1 of
- [] -> TE << L2 >>
- (u2 : u3) ->
- (( \ TE << p >> -> ( TQ << [e | qs] ++ (h u3) >> )) u2)
- [] (h u3)
- in
- h ( TE << L1 >> )
-
-"h", "u1", "u2", and "u3" are new variables.
-\end{verbatim}
-
-@deListComp@ is the TQ translation scheme. Roughly speaking, @dsExpr@
-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 :: [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) ->
-
- -- 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
-
- where
- 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)
-
- -- Last: the one to return
-deListComp [] body list -- Figure 7.4, SLPJ, p 135, rule C above
- = dsLExpr body `thenDs` \ core_body ->
- returnDs (mkConsExpr (exprType core_body) core_body list)
-
- -- Non-last: must be a guard
-deListComp (ExprStmt guard _ _ : quals) body list -- rule B above
- = dsLExpr guard `thenDs` \ core_guard ->
- deListComp quals body list `thenDs` \ core_rest ->
- returnDs (mkIfThenElse core_guard core_rest list)
-
--- [e | let B, qs] = let B in [e | qs]
-deListComp (LetStmt binds : quals) body list
- = deListComp quals body list `thenDs` \ core_rest ->
- dsLocalBinds binds core_rest
-
-deListComp (BindStmt pat list1 _ _ : quals) body core_list2 -- rule A' above
- = dsLExpr list1 `thenDs` \ core_list1 ->
- deBindComp pat core_list1 quals body core_list2
-\end{code}
-
-
-\begin{code}
-deBindComp pat core_list1 quals body 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 = hsPatType 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] ->
-
- -- 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 ->
- let
- 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)
-\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 = let
- f = \ x b -> case x of
- p -> TE[ e | q ] c b
- _ -> b
- in
- foldr f n l
-\end{verbatim}
-
-\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
- = dsLExpr body `thenDs` \ core_body ->
- returnDs (mkApps (Var c_id) [core_body, Var n_id])
-
- -- Non-last: must be a guard
-dfListComp c_id n_id (ExprStmt guard _ _ : quals) body
- = dsLExpr guard `thenDs` \ core_guard ->
- dfListComp c_id n_id quals body `thenDs` \ core_rest ->
- returnDs (mkIfThenElse core_guard core_rest (Var n_id))
-
-dfListComp c_id n_id (LetStmt binds : quals) body
- -- new in 1.3, local bindings
- = dfListComp c_id n_id quals body `thenDs` \ core_rest ->
- dsLocalBinds binds core_rest
-
-dfListComp c_id n_id (BindStmt pat list1 _ _ : quals) body
- -- evaluate the two lists
- = dsLExpr list1 `thenDs` \ core_list1 ->
-
- -- find the required type
- let x_ty = hsPatType pat
- b_ty = idType n_id
- in
-
- -- create some new local id's
- newSysLocalsDs [b_ty,x_ty] `thenDs` \ [b,x] ->
-
- -- build rest of the comprehesion
- dfListComp c_id b quals body `thenDs` \ core_rest ->
-
- -- build the pattern match
- 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 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]
- -> LHsExpr Id
- -> Type -- Don't use; called with `undefined' below
- -> DsM CoreExpr
-dsPArrComp qs body _ =
- dsLookupGlobalId replicatePName `thenDs` \repP ->
- let unitArray = mkApps (Var repP) [Type unitTy,
- mkIntExpr 1,
- mkCoreTup []]
- in
- dePArrComp qs body (mkTuplePat []) unitArray
-
--- the work horse
---
-dePArrComp :: [Stmt Id]
- -> LHsExpr Id
- -> LPat Id -- the current generator pattern
- -> CoreExpr -- the current generator expression
- -> DsM CoreExpr
---
--- <<[:e' | :]>> pa ea = mapP (\pa -> e') ea
---
-dePArrComp [] 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) body pa cea =
- dsLookupGlobalId filterPName `thenDs` \filterP ->
- let ty = parrElemType cea
- 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 = filterP (\x -> case x of {p -> True; _ -> False}) e
--- in
--- <<[:e' | qs:]>> (pa, p) (crossP ea ef)
---
-dePArrComp (BindStmt p e _ _ : qs) body 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' = mkTuplePat [pa, p]
- in
- dePArrComp qs body 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) body pa cea =
- dsLookupGlobalId mapPName `thenDs` \mapP ->
- let xs = map unLoc (collectLocalBinders ds)
- ty'cea = parrElemType cea
- in
- newSysLocalDs ty'cea `thenDs` \v ->
- dsLocalBinds 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' = mkTuplePat [pa, mkTuplePat (map nlVarPat xs)]
- proj = mkLams [v] ccase
- in
- dePArrComp qs body 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 qss : qs) body pa cea =
- dsLookupGlobalId crossPName `thenDs` \crossP ->
- deParStmt qss `thenDs` \(pQss,
- ceQss) ->
- let ty'cea = parrElemType cea
- ty'ceQss = parrElemType ceQss
- pa' = mkTuplePat [pa, pQss]
- in
- dePArrComp qs body pa' (mkApps (Var crossP) [Type ty'cea, Type ty'ceQss,
- cea, ceQss])
- where
- deParStmt [] =
- -- empty parallel statement lists have not source representation
- panic "DsListComp.dePArrComp: Empty parallel list comprehension"
- deParStmt ((qs, xs):qss) = -- first statement
- let res_expr = mkExplicitTuple (map nlHsVar xs)
- in
- dsPArrComp (map unLoc qs) res_expr undefined `thenDs` \cqs ->
- parStmts qss (mkTuplePat (map nlVarPat 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)]
- ty'cea = parrElemType cea
- res_expr = mkExplicitTuple (map nlHsVar xs)
- in
- dsPArrComp (map unLoc qs) res_expr undefined `thenDs` \cqs ->
- let ty'cqs = parrElemType cqs
- cea' = mkApps (Var zipP) [Type ty'cea, Type ty'cqs, cea, cqs]
- in
- parStmts qss 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"
-
--- 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}
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