dsListComp lquals res_ty = do
dflags <- getDOptsDs
let quals = map unLoc lquals
- [elt_ty] = tcTyConAppArgs res_ty
+ 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;
-- 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
+dsInnerListComp (stmts, bndrs)
= do { expr <- dsListComp (stmts ++ [noLoc $ mkLastStmt (mkBigLHsVarTup bndrs)])
- bndrs_tuple_type
+ (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
-
- ; using_args <-
- case maybeByExpr of
- Nothing -> return [expr]
- Just byExpr -> do
- byExpr' <- dsLExpr byExpr
-
- us <- newUniqueSupply
- [tuple_binder] <- newSysLocalsDs [binders_tuple_type]
- let byExprWrapper = mkTupleCase us binders byExpr' tuple_binder (Var tuple_binder)
-
- return [Lam tuple_binder byExprWrapper, expr]
-
- ; 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
- let (fromBinders, toBinders) = unzip binderMap
-
- fromBindersTypes = map idType fromBinders
- toBindersTypes = map idType toBinders
-
- toBindersTupleType = mkBigCoreTupTy toBindersTypes
+dsTransStmt :: Stmt Id -> DsM (CoreExpr, LPat Id)
+dsTransStmt (TransStmt { trS_form = form, trS_stmts = stmts, trS_bndrs = binderMap
+ , trS_by = by, trS_using = using }) = do
+ let (from_bndrs, to_bndrs) = unzip binderMap
+ from_bndrs_tys = map idType from_bndrs
+ to_bndrs_tys = map idType to_bndrs
+ to_bndrs_tup_ty = mkBigCoreTupTy to_bndrs_tys
-- Desugar an inner comprehension which outputs a list of tuples of the "from" binders
- (expr, from_tup_ty) <- dsInnerListComp (stmts, fromBinders)
+ (expr, from_tup_ty) <- dsInnerListComp (stmts, from_bndrs)
-- 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
- ; us <- newUniqueSupply
- ; [from_tup_id] <- newSysLocalsDs [from_tup_ty]
- ; let by_wrap = mkTupleCase us fromBinders by_e'
- from_tup_id (Var from_tup_id)
- ; return [Lam from_tup_id by_wrap, expr] }
+ ; lam <- matchTuple from_bndrs by_e'
+ ; return [lam, expr] }
-- Create an unzip function for the appropriate arity and element types and find "map"
- (unzip_fn, unzip_rhs) <- mkUnzipBind fromBindersTypes
+ unzip_stuff <- mkUnzipBind form from_bndrs_tys
map_id <- dsLookupGlobalId mapName
-- Generate the expressions to build the grouped list
let -- First we apply the grouping function to the inner list
- inner_list_expr = mkApps usingExpr' ((Type from_tup_ty) : usingArgs)
+ inner_list_expr = mkApps usingExpr' usingArgs
-- Then we map our "unzip" across it to turn the lists of tuples into tuples of lists
-- We make sure we instantiate the type variable "a" to be a list of "from" tuples and
-- the "b" to be a tuple of "to" lists!
- unzipped_inner_list_expr = mkApps (Var map_id)
- [Type (mkListTy from_tup_ty), Type toBindersTupleType, Var unzip_fn, inner_list_expr]
-- Then finally we bind the unzip function around that expression
- bound_unzipped_inner_list_expr = Let (Rec [(unzip_fn, unzip_rhs)]) unzipped_inner_list_expr
-
- -- Build a pattern that ensures the consumer binds into the NEW binders, which hold lists rather than single values
- let pat = mkBigLHsVarPatTup toBinders
+ bound_unzipped_inner_list_expr
+ = case unzip_stuff of
+ Nothing -> inner_list_expr
+ Just (unzip_fn, unzip_rhs) -> Let (Rec [(unzip_fn, unzip_rhs)]) $
+ mkApps (Var map_id) $
+ [ Type (mkListTy from_tup_ty)
+ , Type to_bndrs_tup_ty
+ , Var unzip_fn
+ , inner_list_expr]
+
+ -- Build a pattern that ensures the consumer binds into the NEW binders,
+ -- which hold lists rather than single values
+ let pat = mkBigLHsVarPatTup to_bndrs
return (bound_unzipped_inner_list_expr, pat)
-
\end{code}
%************************************************************************
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
+deListComp (stmt@(TransStmt {}) : quals) list = do
+ (inner_list_expr, pat) <- dsTransStmt stmt
deBindComp pat inner_list_expr quals list
deListComp (BindStmt pat list1 _ _ : quals) core_list2 = do -- rule A' above
deBindComp pat core_list1 quals core_list2
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
+ = do { exps_and_qual_tys <- mapM dsInnerListComp stmtss_w_bndrs
+ ; let (exps, qual_tys) = unzip exps_and_qual_tys
- (zip_fn, zip_rhs) <- mkZipBind qual_tys
+ ; (zip_fn, zip_rhs) <- mkZipBind qual_tys
-- 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
-
+ ; deBindComp pat (Let (Rec [(zip_fn, zip_rhs)]) (mkApps (Var zip_fn) exps))
+ quals list }
where
bndrs_s = map snd stmtss_w_bndrs
core_rest <- dfListComp c_id n_id quals
dsLocalBinds binds core_rest
-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
-
-dfListComp c_id n_id (stmt@(GroupStmt {}) : quals) = do
- (inner_list_expr, pat) <- dsGroupStmt stmt
+dfListComp c_id n_id (stmt@(TransStmt {}) : quals) = do
+ (inner_list_expr, pat) <- dsTransStmt stmt
-- Anyway, we bind the newly grouped list via the generic binding function
dfBindComp c_id n_id (pat, inner_list_expr) quals
-- Increasing order of tag
-mkUnzipBind :: [Type] -> DsM (Id, CoreExpr)
+mkUnzipBind :: TransForm -> [Type] -> DsM (Maybe (Id, CoreExpr))
-- mkUnzipBind [t1, t2]
-- = (unzip, \ys :: [(t1, t2)] -> foldr (\ax :: (t1, t2) axs :: ([t1], [t2])
-- -> case ax of
-- ys)
--
-- We use foldr here in all cases, even if rules are turned off, because we may as well!
-mkUnzipBind elt_tys = do
- ax <- newSysLocalDs elt_tuple_ty
- axs <- newSysLocalDs elt_list_tuple_ty
- ys <- newSysLocalDs elt_tuple_list_ty
- xs <- mapM newSysLocalDs elt_tys
- xss <- mapM newSysLocalDs elt_list_tys
+mkUnzipBind ThenForm _
+ = return Nothing -- No unzipping for ThenForm
+mkUnzipBind _ elt_tys
+ = do { ax <- newSysLocalDs elt_tuple_ty
+ ; axs <- newSysLocalDs elt_list_tuple_ty
+ ; ys <- newSysLocalDs elt_tuple_list_ty
+ ; xs <- mapM newSysLocalDs elt_tys
+ ; xss <- mapM newSysLocalDs elt_list_tys
- unzip_fn <- newSysLocalDs unzip_fn_ty
-
- [us1, us2] <- sequence [newUniqueSupply, newUniqueSupply]
-
- let nil_tuple = mkBigCoreTup (map mkNilExpr elt_tys)
-
- concat_expressions = map mkConcatExpression (zip3 elt_tys (map Var xs) (map Var xss))
- tupled_concat_expression = mkBigCoreTup concat_expressions
-
- folder_body_inner_case = mkTupleCase us1 xss tupled_concat_expression axs (Var axs)
- folder_body_outer_case = mkTupleCase us2 xs folder_body_inner_case ax (Var ax)
- folder_body = mkLams [ax, axs] folder_body_outer_case
-
- unzip_body <- mkFoldrExpr elt_tuple_ty elt_list_tuple_ty folder_body nil_tuple (Var ys)
- return (unzip_fn, mkLams [ys] unzip_body)
+ ; unzip_fn <- newSysLocalDs unzip_fn_ty
+
+ ; [us1, us2] <- sequence [newUniqueSupply, newUniqueSupply]
+
+ ; let nil_tuple = mkBigCoreTup (map mkNilExpr elt_tys)
+ concat_expressions = map mkConcatExpression (zip3 elt_tys (map Var xs) (map Var xss))
+ tupled_concat_expression = mkBigCoreTup concat_expressions
+
+ folder_body_inner_case = mkTupleCase us1 xss tupled_concat_expression axs (Var axs)
+ folder_body_outer_case = mkTupleCase us2 xs folder_body_inner_case ax (Var ax)
+ folder_body = mkLams [ax, axs] folder_body_outer_case
+
+ ; unzip_body <- mkFoldrExpr elt_tuple_ty elt_list_tuple_ty folder_body nil_tuple (Var ys)
+ ; return (Just (unzip_fn, mkLams [ys] unzip_body)) }
where
elt_tuple_ty = mkBigCoreTupTy elt_tys
elt_tuple_list_ty = mkListTy elt_tuple_ty
Translation for monad comprehensions
\begin{code}
-
--- | Keep the "context" of a monad comprehension in a small data type to avoid
--- some boilerplate...
-data DsMonadComp = DsMonadComp
- { mc_return :: Either (SyntaxExpr Id) (Expr CoreBndr)
- , mc_body :: LHsExpr Id
- , mc_m_ty :: Type
- }
-
---
-- Entry point for monad comprehension desugaring
---
-dsMonadComp :: [LStmt Id] -- the statements
- -> Type -- the final type
- -> DsM CoreExpr
-dsMonadComp stmts res_ty
- = dsMcStmts stmts (DsMonadComp (Left return_op) body m_ty)
- where
- (m_ty, _) = tcSplitAppTy res_ty
-
-
-dsMcStmts :: [LStmt Id]
- -> DsMonadComp
- -> DsM CoreExpr
-
--- No statements left for desugaring. Desugar the body after calling "return"
--- on it.
-dsMcStmts [] DsMonadComp { mc_return, mc_body }
- = case mc_return of
- Left ret -> dsLExpr $ noLoc ret `nlHsApp` mc_body
- Right ret' -> do
- { body' <- dsLExpr mc_body
- ; return $ mkApps ret' [body'] }
-
--- Otherwise desugar each statement step by step
-dsMcStmts ((L loc stmt) : lstmts) mc
- = putSrcSpanDs loc (dsMcStmt stmt lstmts mc)
+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
; 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 |]
+-- case unzip n_tup of qv' -> [| rest |]
--
-- where variables (v1:t1, ..., vk:tk) are bound by q
-- qv = (v1, ..., vk)
-- f :: forall a. (a -> t) -> m1 a -> m2 (n a)
-- n_tup :: n qt
-- unzip :: n qt -> (n t1, ..., n tk) (needs Functor n)
---
--- [| q, then group by e using f |] -> (f (\q_v -> e) [| q |]) >>= (return . (unzip q_v))
---
--- which is equal to
---
--- [| q, then group by e using f |] -> liftM (unzip q_v) (f (\q_v -> e) [| q |])
---
--- where unzip is of the form
---
--- unzip :: n (a,b,c,..) -> (n a,n b,n c,..)
--- unzip m_tuple = ( fmap selN1 m_tuple
--- , fmap selN2 m_tuple
--- , .. )
--- where selN1 (a,b,c,..) = a
--- selN2 (a,b,c,..) = b
--- ..
---
-dsMcStmt (GroupStmt stmts binderMap by using return_op bind_op fmap_op) stmts_rest
- = do { let (fromBinders, toBinders) = unzip binderMap
- fromBindersTypes = map idType fromBinders -- Types ty
- fromBindersTupleTy = mkBigCoreTupTy fromBindersTypes
- toBindersTypes = map idType toBinders -- Types (n ty)
- toBindersTupleTy = mkBigCoreTupTy toBindersTypes
+
+dsMcStmt (TransStmt { trS_stmts = stmts, trS_bndrs = bndrs
+ , trS_by = by, trS_using = using
+ , trS_ret = return_op, trS_bind = bind_op
+ , trS_fmap = fmap_op, trS_form = form }) 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 fromBinders return_op
+ ; 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 (either id noLoc using)
+ ; usingExpr' <- dsLExpr using
; usingArgs <- case by of
Nothing -> return [expr]
Just by_e -> do { by_e' <- dsLExpr by_e
- ; lam <- matchTuple fromBinders by_e'
+ ; lam <- matchTuple from_bndrs by_e'
; return [lam, expr] }
- -- Create an unzip function for the appropriate arity and element types
- ; fmap_op' <- dsExpr fmap_op
- ; (unzip_fn, unzip_rhs) <- mkMcUnzipM fmap_op' m_ty fromBindersTypes
-
-- 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
; 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
-
- ; body <- dsMcStmts stmts_rest
- ; n_tup_var <- newSysLocalDs n_tup_ty
- ; tup_n_var <- newSysLocalDs (mkBigCoreVarTupTy toBinders)
- ; us <- newUniqueSupply
- ; let unzip_n_tup = Let (Rec [(unzip_fn, unzip_rhs)]) $
- App (Var unzip_fn) (Var n_tup_var)
- -- unzip_n_tup :: (n a, n b, n c)
- body' = mkTupleCase us toBinders body unzip_n_tup (Var tup_n_var)
+ ; 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 form 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']) }
-- 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 <- mapM ds_inner pairs
- ; let qual_tys = map (mkBigCoreVarTupTy . snd) pairs
- ; mzip_op' <- dsExpr mzip_op
- ; (zip_fn, zip_rhs) <- mkMcZipM mzip_op' (mc_m_ty mc) qual_tys
+ = do { exps_w_tys <- mapM ds_inner pairs -- Pairs (exp :: m ty, ty)
+ ; mzip_op' <- dsExpr mzip_op
; let -- The pattern variables
- vars = map (mkBigLHsVarPatTup . snd) pairs
+ pats = map (mkBigLHsVarPatTup . snd) pairs
-- Pattern with tuples of variables
-- [v1,v2,v3] => (v1, (v2, v3))
- pat = foldr (\tn tm -> mkBigLHsPatTup [tn, tm]) (last vars) (init vars)
- rhs = Let (Rec [(zip_fn, zip_rhs)]) (mkApps (Var zip_fn) exps)
+ 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) = dsInnerMonadComp stmts bndrs mono_ret_op
+ ds_inner (stmts, bndrs) = do { exp <- dsInnerMonadComp stmts bndrs mono_ret_op
+ ; return (exp, tup_ty) }
where
- mono_ret_op = HsWrap (WpTyApp (mkBigCoreVarTupTy bndrs)) return_op
+ mono_ret_op = HsWrap (WpTyApp tup_ty) return_op
+ tup_ty = mkBigCoreVarTupTy bndrs
dsMcStmt stmt _ = pprPanic "dsMcStmt: unexpected stmt" (ppr stmt)
-- \x. case x of (a,b,c) -> body
matchTuple ids body
= do { us <- newUniqueSupply
- ; tup_id <- newSysLocalDs (mkBigLHsVarPatTup ids)
+ ; 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
dsInnerMonadComp :: [LStmt Id]
-> [Id] -- Return a tuple of these variables
- -> LHsExpr Id -- The monomorphic "return" operator
+ -> HsExpr Id -- The monomorphic "return" operator
-> DsM CoreExpr
dsInnerMonadComp stmts bndrs ret_op
- = dsMcStmts (stmts ++ [noLoc (ReturnStmt (mkBigLHsVarTup bndrs) ret_op)])
+ = dsMcStmts (stmts ++ [noLoc (LastStmt (mkBigLHsVarTup bndrs) ret_op)])
-- The `unzip` function for `GroupStmt` in a monad comprehensions
--
-- , liftM selN2 m_tuple
-- , .. )
--
--- mkMcUnzipM m [t1, t2]
--- = (unzip_fn, \ys :: m (t1, t2) ->
--- ( liftM (selN1 :: (t1, t2) -> t1) ys
--- , liftM (selN2 :: (t1, t2) -> t2) ys
--- ))
---
-mkMcUnzipM :: CoreExpr
- -> Type -- m
- -> [Type] -- [a,b,c,..]
- -> DsM (Id, CoreExpr)
-mkMcUnzipM liftM_op m_ty elt_tys
- = do { ys <- newSysLocalDs monad_tuple_ty
- ; xs <- mapM newSysLocalDs elt_tys
- ; scrut <- newSysLocalDs tuple_tys
-
- ; unzip_fn <- newSysLocalDs unzip_fn_ty
-
- ; let -- Select one Id from our tuple
- selectExpr n = mkLams [scrut] $ mkTupleSelector xs (xs !! n) scrut (Var scrut)
- -- Apply 'selectVar' and 'ys' to 'liftM'
- tupleElem n = mkApps liftM_op
- -- Types (m is figured out by the type checker):
- -- liftM :: forall a b. (a -> b) -> m a -> m b
- [ Type tuple_tys, Type (elt_tys !! n)
- -- Arguments:
- , selectExpr n, Var ys ]
- -- The final expression with the big tuple
- unzip_body = mkBigCoreTup [ tupleElem n | n <- [0..length elt_tys - 1] ]
-
- ; return (unzip_fn, mkLams [ys] unzip_body) }
- where monad_tys = map (m_ty `mkAppTy`) elt_tys -- [m a,m b,m c,..]
- tuple_monad_tys = mkBigCoreTupTy monad_tys -- (m a,m b,m c,..)
- tuple_tys = mkBigCoreTupTy elt_tys -- (a,b,c,..)
- monad_tuple_ty = m_ty `mkAppTy` tuple_tys -- m (a,b,c,..)
- unzip_fn_ty = monad_tuple_ty `mkFunTy` tuple_monad_tys -- m (a,b,c,..) -> (m a,m b,m c,..)
-
--- Generate the `mzip` function for `ParStmt` in monad comprehensions, for
--- example:
---
--- mzip :: m t1
--- -> (m t2 -> m t3 -> m (t2, t3))
--- -> m (t1, (t2, t3))
---
--- mkMcZipM m [t1, t2, t3]
--- = (zip_fn, \(q1::t1) (q2::t2) (q3::t3) ->
--- mzip q1 (mzip q2 q3))
---
-mkMcZipM :: CoreExpr
- -> Type
- -> [Type]
- -> DsM (Id, CoreExpr)
-
-mkMcZipM mzip_op m_ty tys@(_:_:_) -- min. 2 types
- = do { (ids, t1, tuple_ty, zip_body) <- loop tys
- ; zip_fn <- newSysLocalDs $
- (m_ty `mkAppTy` t1)
- `mkFunTy`
- (m_ty `mkAppTy` tuple_ty)
- `mkFunTy`
- (m_ty `mkAppTy` mkBigCoreTupTy [t1, tuple_ty])
- ; return (zip_fn, mkLams ids zip_body) }
-
- where
- -- loop :: [Type] -> DsM ([Id], Type, [Type], CoreExpr)
- loop [t1, t2] = do -- last run of the `loop`
- { ids@[a,b] <- newSysLocalsDs (map (m_ty `mkAppTy`) [t1,t2])
- ; let zip_body = mkApps mzip_op [ Type t1, Type t2 , Var a, Var b ]
- ; return (ids, t1, t2, zip_body) }
-
- loop (t1:tr) = do
- { -- Get ty, ids etc from the "inner" zip
- (ids', t1', t2', zip_body') <- loop tr
-
- ; a <- newSysLocalDs $ m_ty `mkAppTy` t1
- ; let tuple_ty' = mkBigCoreTupTy [t1', t2']
- zip_body = mkApps mzip_op [ Type t1, Type tuple_ty', Var a, zip_body' ]
- ; return ((a:ids'), t1, tuple_ty', zip_body) }
-
--- This case should never happen:
-mkMcZipM _ _ tys = pprPanic "mkMcZipM: unexpected argument" (ppr tys)
-
+-- mkMcUnzipM fmap ys [t1, t2]
+-- = ( fmap (selN1 :: (t1, t2) -> t1) ys
+-- , fmap (selN2 :: (t1, t2) -> t2) ys )
+
+mkMcUnzipM :: TransForm
+ -> SyntaxExpr TcId -- fmap
+ -> Id -- Of type n (a,b,c)
+ -> [Type] -- [a,b,c]
+ -> DsM CoreExpr -- Of type (n a, n b, n c)
+mkMcUnzipM ThenForm _ ys _
+ = return (Var ys) -- No unzipping to do
+
+mkMcUnzipM _ fmap_op ys elt_tys
+ = do { fmap_op' <- dsExpr fmap_op
+ ; xs <- mapM newSysLocalDs elt_tys
+ ; let tup_ty = mkBigCoreTupTy elt_tys
+ ; tup_xs <- newSysLocalDs tup_ty
+
+ ; let mk_elt i = mkApps fmap_op' -- fmap :: forall a b. (a -> b) -> n a -> n b
+ [ Type tup_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}
projects / ghc-hetmet.git / blobdiff