%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[DsListComp]{Desugaring list comprehensions}
\begin{code}
-#include "HsVersions.h"
-
module DsListComp ( dsListComp ) where
-IMP_Ubiq()
-#if defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ <= 201
-IMPORT_DELOOPER(DsLoop) -- break dsExpr-ish loop
-#else
-import {-# SOURCE #-} DsExpr ( dsExpr )
-import {-# SOURCE #-} DsBinds ( dsBinds )
-#endif
+#include "HsVersions.h"
+
+import {-# SOURCE #-} DsExpr ( dsExpr, dsLet )
-import HsSyn ( Stmt(..), HsExpr, HsBinds )
-import TcHsSyn ( SYN_IE(TypecheckedStmt), SYN_IE(TypecheckedHsExpr) , SYN_IE(TypecheckedHsBinds) )
+import HsSyn ( Stmt(..), HsExpr )
+import TcHsSyn ( TypecheckedStmt, TypecheckedHsExpr )
import DsHsSyn ( outPatType )
import CoreSyn
import DsUtils
import CmdLineOpts ( opt_FoldrBuildOn )
-import CoreUtils ( coreExprType, mkCoreIfThenElse )
-import Id ( SYN_IE(Id) )
-import PrelVals ( mkBuild, foldrId )
-import Type ( mkTyVarTy, mkForAllTy, mkFunTys, mkFunTy, SYN_IE(Type) )
-import TysPrim ( alphaTy )
+import CoreUtils ( coreExprType )
+import Id ( idType )
+import Var ( Id, TyVar )
+import Const ( Con(..) )
+import PrelInfo ( foldrId, buildId )
+import Type ( mkTyVarTy, mkForAllTy, mkFunTys, mkFunTy, Type )
+import TysPrim ( alphaTyVar, alphaTy )
import TysWiredIn ( nilDataCon, consDataCon, listTyCon )
-import TyVar ( alphaTyVar )
import Match ( matchSimply )
-import Util ( panic )
+import Outputable
\end{code}
List comprehensions may be desugared in one of two ways: ``ordinary''
dsListComp quals elt_ty
| not opt_FoldrBuildOn -- Be boring
- = deListComp quals nil_expr
+ = deListComp quals (mkNilExpr elt_ty)
| otherwise -- foldr/build lives!
= newTyVarsDs [alphaTyVar] `thenDs` \ [n_tyvar] ->
let
- alpha_to_alpha = alphaTy `mkFunTy` alphaTy
-
n_ty = mkTyVarTy n_tyvar
c_ty = mkFunTys [elt_ty, n_ty] n_ty
- g_ty = mkForAllTy alphaTyVar (
- (elt_ty `mkFunTy` alpha_to_alpha)
- `mkFunTy`
- alpha_to_alpha
- )
in
- newSysLocalsDs [c_ty,n_ty,g_ty] `thenDs` \ [c, n, g] ->
+ newSysLocalsDs [c_ty,n_ty] `thenDs` \ [c, n] ->
- dfListComp c_ty c
- n_ty n
- quals `thenDs` \ result ->
+ dfListComp c n quals `thenDs` \ result ->
- returnDs (mkBuild elt_ty n_tyvar c n g result)
- where
- nil_expr = mkCon nilDataCon [] [elt_ty] []
+ returnDs (Var buildId `App` Type elt_ty
+ `App` mkLams [n_tyvar, c, n] result)
\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.
+
\begin{code}
deListComp :: [TypecheckedStmt] -> CoreExpr -> DsM CoreExpr
-deListComp [ReturnStmt expr] list -- Figure 7.4, SLPJ, p 135, rule C above
+deListComp [ReturnStmt expr] list -- Figure 7.4, SLPJ, p 135, rule C above
= dsExpr expr `thenDs` \ core_expr ->
- mkConDs consDataCon [TyArg (coreExprType core_expr), VarArg core_expr, VarArg list]
+ returnDs (mkConsExpr (coreExprType core_expr) core_expr list)
deListComp (GuardStmt guard locn : quals) list -- rule B above
= dsExpr guard `thenDs` \ core_guard ->
deListComp quals list `thenDs` \ core_rest ->
- returnDs (mkCoreIfThenElse core_guard core_rest list)
+ returnDs (mkIfThenElse core_guard core_rest list)
-- [e | let B, qs] = let B in [e | qs]
deListComp (LetStmt binds : quals) list
- = dsBinds False{-don't auto scc-} binds `thenDs` \ core_binds ->
- deListComp quals list `thenDs` \ core_rest ->
- returnDs (mkCoLetsAny core_binds core_rest)
+ = 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 ->
newSysLocalsDs [h_ty, u1_ty, u2_ty, u3_ty] `thenDs` \ [h, u1, u2, u3] ->
-- the "fail" value ...
- mkAppDs (Var h) [VarArg (Var u3)] `thenDs` \ core_fail ->
+ let
+ core_fail = App (Var h) (Var u3)
+ letrec_body = App (Var h) core_list1
+ in
deListComp quals core_fail `thenDs` \ rest_expr ->
- matchSimply (Var u2) pat res_ty
+ matchSimply (Var u2) ListCompMatch pat
rest_expr core_fail `thenDs` \ core_match ->
- mkAppDs (Var h) [VarArg core_list1] `thenDs` \ letrec_body ->
-
- returnDs (
- mkCoLetrecAny [
- ( h,
- (Lam (ValBinder u1)
- (Case (Var u1)
- (AlgAlts
- [(nilDataCon, [], core_list2),
- (consDataCon, [u2, u3], core_match)]
- NoDefault)))
- )] letrec_body
- )
+ let
+ rhs = Lam u1 $
+ Case (Var u1) u1 [(DataCon nilDataCon, [], core_list2),
+ (DataCon consDataCon, [u2, u3], core_match)]
+ in
+ returnDs (Let (Rec [(h, rhs)]) letrec_body)
\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 = foldr
- (\ TE << p >> b -> TE << [ e | q ] >> c b
- _ b -> b) n l
+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 :: Type -> Id -- 'c'; its type and id
- -> Type -> Id -- 'n'; its type and id
+dfListComp :: Id -> Id -- 'c' and 'n'
-> [TypecheckedStmt] -- the rest of the qual's
-> DsM CoreExpr
-dfListComp c_ty c_id n_ty n_id [ReturnStmt expr]
+dfListComp c_id n_id [ReturnStmt expr]
= dsExpr expr `thenDs` \ core_expr ->
- mkAppDs (Var c_id) [VarArg core_expr, VarArg (Var n_id)]
+ returnDs (mkApps (Var c_id) [core_expr, Var n_id])
-dfListComp c_ty c_id n_ty n_id (GuardStmt guard locn : quals)
+dfListComp c_id n_id (GuardStmt guard locn : quals)
= dsExpr guard `thenDs` \ core_guard ->
- dfListComp c_ty c_id n_ty n_id quals `thenDs` \ core_rest ->
- returnDs (mkCoreIfThenElse core_guard core_rest (Var n_id))
+ dfListComp c_id n_id quals `thenDs` \ core_rest ->
+ returnDs (mkIfThenElse core_guard core_rest (Var n_id))
-dfListComp c_ty c_id n_ty n_id (LetStmt binds : quals)
+dfListComp c_id n_id (LetStmt binds : quals)
-- new in 1.3, local bindings
- = dsBinds False{-don't auto scc-} binds `thenDs` \ core_binds ->
- dfListComp c_ty c_id n_ty n_id quals `thenDs` \ core_rest ->
- returnDs (mkCoLetsAny core_binds core_rest)
+ = dfListComp c_id n_id quals `thenDs` \ core_rest ->
+ dsLet binds core_rest
-dfListComp c_ty c_id n_ty n_id (BindStmt pat list1 locn : quals)
+dfListComp c_id n_id (BindStmt pat list1 locn : quals)
-- evaluate the two lists
= dsExpr list1 `thenDs` \ core_list1 ->
-- find the required type
-
- let p_ty = outPatType pat
- b_ty = n_ty -- alias b_ty to n_ty
- fn_ty = mkFunTys [p_ty, b_ty] b_ty
- lst_ty = coreExprType core_list1
+ let x_ty = outPatType pat
+ b_ty = idType n_id
in
-- create some new local id's
-
- newSysLocalsDs [b_ty,p_ty,fn_ty,lst_ty] `thenDs` \ [b,p,fn,lst] ->
+ newSysLocalsDs [b_ty,x_ty] `thenDs` \ [b,x] ->
-- build rest of the comprehesion
+ dfListComp c_id b quals `thenDs` \ core_rest ->
- dfListComp c_ty c_id b_ty b quals `thenDs` \ core_rest ->
-- build the pattern match
-
- matchSimply (Var p) pat b_ty core_rest (Var b) `thenDs` \ core_expr ->
+ matchSimply (Var x) ListCompMatch pat core_rest (Var b) `thenDs` \ core_expr ->
-- now build the outermost foldr, and return
-
returnDs (
- mkCoLetsAny
- [NonRec fn (mkValLam [p, b] core_expr),
- NonRec lst core_list1]
- (mkFoldr p_ty n_ty fn n_id lst)
+ Var foldrId `App` Type x_ty
+ `App` Type b_ty
+ `App` mkLams [x, b] core_expr
+ `App` Var n_id
+ `App` core_list1
)
-
-mkFoldr a b f z xs
- = mkValApp (mkTyApp (Var foldrId) [a,b]) [VarArg f, VarArg z, VarArg xs]
\end{code}
+
+
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