Commit d76d9636 authored by Simon Peyton Jones's avatar Simon Peyton Jones
Browse files

More hacking on monad-comp; now works

parent 4ac2bb39
......@@ -463,14 +463,18 @@ addTickStmt isGuard (TransformStmt stmts ids usingExpr maybeByExpr returnExpr bi
t_b <- (addTickSyntaxExpr hpcSrcSpan bindExpr)
return $ TransformStmt t_s ids t_u t_m t_r t_b
addTickStmt isGuard (GroupStmt stmts binderMap by using returnExpr bindExpr liftMExpr) = do
t_s <- (addTickLStmts isGuard stmts)
t_y <- (fmapMaybeM addTickLHsExprAlways by)
t_u <- (fmapEitherM addTickLHsExprAlways (addTickSyntaxExpr hpcSrcSpan) using)
t_f <- (addTickSyntaxExpr hpcSrcSpan returnExpr)
t_b <- (addTickSyntaxExpr hpcSrcSpan bindExpr)
t_m <- (addTickSyntaxExpr hpcSrcSpan liftMExpr)
return $ GroupStmt t_s binderMap t_y t_u t_b t_f t_m
addTickStmt isGuard stmt@(GroupStmt { grpS_stmts = stmts
, grpS_by = by, grpS_using = using
, grpS_ret = returnExpr, grpS_bind = bindExpr
, grpS_fmap = liftMExpr }) = do
t_s <- addTickLStmts isGuard stmts
t_y <- fmapMaybeM addTickLHsExprAlways by
t_u <- addTickLHsExprAlways using
t_f <- addTickSyntaxExpr hpcSrcSpan returnExpr
t_b <- addTickSyntaxExpr hpcSrcSpan bindExpr
t_m <- addTickSyntaxExpr hpcSrcSpan liftMExpr
return $ stmt { grpS_stmts = t_s, grpS_by = t_y, grpS_using = t_u
, grpS_ret = t_f, grpS_bind = t_b, grpS_fmap = t_m }
addTickStmt isGuard stmt@(RecStmt {})
= do { stmts' <- addTickLStmts isGuard (recS_stmts stmt)
......
......@@ -327,10 +327,10 @@ dsExpr (HsLet binds body) = do
--
dsExpr (HsDo ListComp stmts res_ty) = dsListComp stmts res_ty
dsExpr (HsDo PArrComp stmts _) = dsPArrComp (map unLoc stmts)
dsExpr (HsDo DoExpr stmts res_ty) = dsDo stmts res_ty
dsExpr (HsDo GhciStmt stmts res_ty) = dsDo stmts res_ty
dsExpr (HsDo MDoExpr stmts res_ty) = dsDo stmts res_ty
dsExpr (HsDo MonadComp stmts res_ty) = dsMonadComp stmts res_ty
dsExpr (HsDo DoExpr stmts _) = dsDo stmts
dsExpr (HsDo GhciStmt stmts _) = dsDo stmts
dsExpr (HsDo MDoExpr stmts _) = dsDo stmts
dsExpr (HsDo MonadComp stmts _) = dsMonadComp stmts
dsExpr (HsIf mb_fun guard_expr then_expr else_expr)
= do { pred <- dsLExpr guard_expr
......@@ -694,21 +694,16 @@ handled in DsListComp). Basically does the translation given in the
Haskell 98 report:
\begin{code}
dsDo :: [LStmt Id]
-> Type -- Type of the whole expression
-> DsM CoreExpr
dsDo stmts result_ty
dsDo :: [LStmt Id] -> DsM CoreExpr
dsDo stmts
= goL stmts
where
goL [] = panic "dsDo"
goL (L loc stmt:lstmts) = putSrcSpanDs loc (go loc stmt lstmts)
go _ (LastStmt body ret_op) stmts
= ASSERT( null stmts )
do { body' <- dsLExpr body
; ret_op' <- dsExpr ret_op
; return (App ret_op' body') }
go _ (LastStmt body _) stmts
= ASSERT( null stmts ) dsLExpr body
-- The 'return' op isn't used for 'do' expressions
go _ (ExprStmt rhs then_expr _ _) stmts
= do { rhs2 <- dsLExpr rhs
......@@ -753,7 +748,7 @@ dsDo stmts result_ty
(mkFunTy tup_ty body_ty))
mfix_pat = noLoc $ LazyPat $ mkLHsPatTup rec_tup_pats
body = noLoc $ HsDo DoExpr (rec_stmts ++ [ret_stmt]) body_ty
ret_stmt = noLoc $ LastStmt return_op (mkLHsTupleExpr rets)
ret_stmt = noLoc $ LastStmt (mkLHsTupleExpr rets) return_op
tup_ty = mkBoxedTupleTy (map idType tup_ids) -- Deals with singleton case
handle_failure :: LPat Id -> MatchResult -> SyntaxExpr Id -> DsM CoreExpr
......
......@@ -54,7 +54,9 @@ dsListComp :: [LStmt Id]
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;
......@@ -82,9 +84,9 @@ dsListComp lquals res_ty = do
-- 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
......@@ -117,7 +119,8 @@ dsTransformStmt (TransformStmt stmts binders usingExpr maybeByExpr _ _)
-- 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
......@@ -688,45 +691,15 @@ parrElemType e =
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
......@@ -785,7 +758,7 @@ dsMcStmt (TransformStmt stmts binders usingExpr maybeByExpr return_op bind_op) s
--
-- [| (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)
......@@ -794,61 +767,42 @@ dsMcStmt (TransformStmt stmts binders usingExpr maybeByExpr return_op bind_op) s
-- 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 (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 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
; 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_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 (mkBigCoreVarTupTy toBinders)
; tup_n_var <- newSysLocalDs tup_n_ty
; tup_n_expr <- mkMcUnzipM fmap_op' n_tup_var from_bndr_tys
; 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 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']) }
......@@ -864,23 +818,26 @@ dsMcStmt (GroupStmt stmts binderMap by using return_op bind_op fmap_op) stmts_re
-- 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
= do { exps_w_tys <- mapM ds_inner pairs -- Pairs (exp :: m ty, ty)
; mzip_op' <- dsExpr mzip_op
; (zip_fn, zip_rhs) <- mkMcZipM mzip_op' (mc_m_ty mc) qual_tys
; 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)
......@@ -891,10 +848,9 @@ matchTuple :: [Id] -> CoreExpr -> DsM CoreExpr
-- \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
......@@ -936,10 +892,10 @@ dsMcBindStmt pat rhs' bind_op fail_op stmts
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
--
......@@ -948,85 +904,25 @@ dsInnerMonadComp stmts bndrs ret_op
-- , 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) }
-- mkMcUnzipM fmap ys [t1, t2]
-- = ( fmap (selN1 :: (t1, t2) -> t1) ys
-- , fmap (selN2 :: (t1, t2) -> t2) ys )
loop (t1:tr) = do
{ -- Get ty, ids etc from the "inner" zip
(ids', t1', t2', zip_body') <- loop tr
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)
; 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) }
; 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]
-- This case should never happen:
mkMcZipM _ _ tys = pprPanic "mkMcZipM: unexpected argument" (ppr tys)
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}
......@@ -721,19 +721,15 @@ repE (HsLet bs e) = do { (ss,ds) <- repBinds bs
; wrapGenSyms ss z }
-- FIXME: I haven't got the types here right yet
repE e@(HsDo ctxt sts body _ _)
repE e@(HsDo ctxt sts _)
| case ctxt of { DoExpr -> True; GhciStmt -> True; _ -> False }
= do { (ss,zs) <- repLSts sts;
body' <- addBinds ss $ repLE body;
ret <- repNoBindSt body';
e' <- repDoE (nonEmptyCoreList (zs ++ [ret]));
e' <- repDoE (nonEmptyCoreList zs);
wrapGenSyms ss e' }
| ListComp <- ctxt
= do { (ss,zs) <- repLSts sts;
body' <- addBinds ss $ repLE body;
ret <- repNoBindSt body';
e' <- repComp (nonEmptyCoreList (zs ++ [ret]));
e' <- repComp (nonEmptyCoreList zs);
wrapGenSyms ss e' }
| otherwise
......
......@@ -522,12 +522,15 @@ cvtHsDo do_or_lc stmts
| null stmts = failWith (ptext (sLit "Empty stmt list in do-block"))
| otherwise
= do { stmts' <- cvtStmts stmts
; body <- case last stmts' of
L _ (ExprStmt body _ _ _) -> return body
stmt' -> failWith (bad_last stmt')
; return $ HsDo do_or_lc (init stmts') body noSyntaxExpr void }
; let Just (stmts'', last') = snocView stmts'
; last'' <- case last' of
L loc (ExprStmt body _ _ _) -> return (L loc (mkLastStmt body))
_ -> failWith (bad_last last')
; return $ HsDo do_or_lc (stmts'' ++ [last'']) void }
where
bad_last stmt = vcat [ ptext (sLit "Illegal last statement of") <+> pprStmtContext do_or_lc <> colon
bad_last stmt = vcat [ ptext (sLit "Illegal last statement of") <+> pprAStmtContext do_or_lc <> colon
, nest 2 $ Outputable.ppr stmt
, ptext (sLit "(It should be an expression.)") ]
......
......@@ -24,6 +24,7 @@ import BasicTypes
import DataCon
import SrcLoc
import Util( dropTail )
import StaticFlags( opt_PprStyle_Debug )
import Outputable
import FastString
......@@ -836,17 +837,19 @@ data StmtLR idL idR
-- Not used for GhciStmt, PatGuard, which scope over other stuff
(LHsExpr idR)
(SyntaxExpr idR) -- The return operator, used only for MonadComp
-- For ListComp, PArrComp, we use the baked-in 'return'
-- For DoExpr, MDoExpr, we don't appply a 'return' at all
-- See Note [Monad Comprehensions]
| BindStmt (LPat idL)
(LHsExpr idR)
(SyntaxExpr idR) -- The (>>=) operator
(SyntaxExpr idR) -- The (>>=) operator; see Note [The type of bind]
(SyntaxExpr idR) -- The fail operator
-- The fail operator is noSyntaxExpr
-- if the pattern match can't fail
| ExprStmt (LHsExpr idR) -- See Note [ExprStmt]
(SyntaxExpr idR) -- The (>>) operator
(SyntaxExpr idR) -- The `guard` operator
(SyntaxExpr idR) -- The `guard` operator; used only in MonadComp
-- See notes [Monad Comprehensions]
PostTcType -- Element type of the RHS (used for arrows)
......@@ -859,16 +862,15 @@ data StmtLR idL idR
(SyntaxExpr idR) -- Polymorphic `return` operator
-- with type (forall a. a -> m a)
-- See notes [Monad Comprehensions]
-- After renaming, the ids are the binders bound by the stmts and used
-- after them
-- After renaming, the ids are the binders
-- bound by the stmts and used after them
-- "qs, then f by e" ==> TransformStmt qs binders f (Just e) (return) (>>=)
-- "qs, then f" ==> TransformStmt qs binders f Nothing (return) (>>=)
| TransformStmt
[LStmt idL] -- Stmts are the ones to the left of the 'then'
[idR] -- After renaming, the IDs are the binders occurring
[idR] -- After renaming, the Ids are the binders occurring
-- within this transform statement that are used after it
(LHsExpr idR) -- "then f"
......@@ -880,25 +882,30 @@ data StmtLR idL idR
(SyntaxExpr idR) -- The '(>>=)' operator.
-- See Note [Monad Comprehensions]
| GroupStmt
[LStmt idL] -- Stmts to the *left* of the 'group'
| GroupStmt {
grpS_stmts :: [LStmt idL], -- Stmts to the *left* of the 'group'
-- which generates the tuples to be grouped
[(idR, idR)] -- See Note [GroupStmt binder map]
grpS_bndrs :: [(idR, idR)], -- See Note [GroupStmt binder map]
(Maybe (LHsExpr idR)) -- "by e" (optional)
grpS_by :: Maybe (LHsExpr idR), -- "by e" (optional)
(Either -- "using f"
(LHsExpr idR) -- Left f => explicit "using f"
(SyntaxExpr idR)) -- Right f => implicit; filled in with 'groupWith'
-- (list comprehensions) or 'groupM' (monad
-- comprehensions)
grpS_using :: LHsExpr idR,
grpS_explicit :: Bool, -- True <=> explicit "using f"
-- False <=> implicit; grpS_using is filled in with
-- 'groupWith' (list comprehensions) or
-- 'groupM' (monad comprehensions)
(SyntaxExpr idR) -- The 'return' function for inner monad
-- Invariant: if grpS_explicit = False, then grp_by = Just e
-- That is, we can have group by e
-- group using f
-- group by e using f
grpS_ret :: SyntaxExpr idR, -- The 'return' function for inner monad
-- comprehensions
(SyntaxExpr idR) -- The '(>>=)' operator
(SyntaxExpr idR) -- The 'liftM' function from Control.Monad for desugaring
-- See Note [Monad Comprehensions]
grpS_bind :: SyntaxExpr idR, -- The '(>>=)' operator
grpS_fmap :: SyntaxExpr idR -- The polymorphic 'fmap' function for desugaring
} -- See Note [Monad Comprehensions]
-- Recursive statement (see Note [How RecStmt works] below)
| RecStmt
......@@ -937,6 +944,17 @@ data StmtLR idL idR
deriving (Data, Typeable)
\end{code}
Note [The type of bind in Stmts]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Some Stmts, notably BindStmt, keep the (>>=) bind operator.
We do NOT assume that it has type
(>>=) :: m a -> (a -> m b) -> m b
In some cases (see Trac #303, #1537) it might have a more
exotic type, such as
(>>=) :: m i j a -> (a -> m j k b) -> m i k b
So we must be careful not to make assumptions about the type.
In particular, the monad may not be uniform throughout.
Note [GroupStmt binder map]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
The [(idR,idR)] in a GroupStmt behaves as follows:
......@@ -986,7 +1004,7 @@ depends on the context. Consider the following contexts:
E :: Bool
Translation: guard E >> ...
Array comprehensions are handled like list comprehensions -=chak
Array comprehensions are handled like list comprehensions.
Note [How RecStmt works]
~~~~~~~~~~~~~~~~~~~~~~~~
......@@ -1045,7 +1063,7 @@ In transform and grouping statements ('then ..' and 'then group ..') the
=>
f [ env | stmts ] >>= \bndrs -> [ body | rest ]
Normal expressions require the 'Control.Monad.guard' function for boolean
ExprStmts require the 'Control.Monad.guard' function for boolean
expressions:
[ body | exp, stmts ]
......@@ -1082,8 +1100,8 @@ pprStmt (ParStmt stmtss _ _ _) = hsep (map doStmts stmtss)
pprStmt (TransformStmt stmts bndrs using by _ _)
= sep (ppr_lc_stmts stmts ++ [pprTransformStmt bndrs using by])
pprStmt (GroupStmt stmts _ by using _ _ _)
= sep (ppr_lc_stmts stmts ++ [pprGroupStmt by using])
pprStmt (GroupStmt { grpS_stmts = stmts, grpS_by = by, grpS_using = using, grpS_explicit = explicit })
= sep (ppr_lc_stmts stmts ++ [pprGroupStmt by using explicit])
pprStmt (RecStmt { recS_stmts = segment, recS_rec_ids = rec_ids
, recS_later_ids = later_ids })
......@@ -1099,13 +1117,13 @@ pprTransformStmt bndrs using by
, nest 2 (pprBy by)]
pprGroupStmt :: OutputableBndr id => Maybe (LHsExpr id)
-> Either (LHsExpr id) (SyntaxExpr is)
-> LHsExpr id -> Bool
-> SDoc
pprGroupStmt by using
= sep [ ptext (sLit "then group"), nest 2 (pprBy by), nest 2 (ppr_using using)]
pprGroupStmt by using explicit
= sep [ ptext (sLit "then group"), nest 2 (pprBy by), nest 2 pp_using ]
where
ppr_using (Right _) = empty
ppr_using (Left e) = ptext (sLit "using") <+> ppr e
pp_using | explicit = ptext (sLit "using") <+> ppr using
| otherwise = empty
pprBy :: OutputableBndr id => Maybe (LHsExpr id) -> SDoc
pprBy Nothing = empty
......@@ -1124,7 +1142,7 @@ ppr_do_stmts :: OutputableBndr id => [LStmt id] -> SDoc
-- Print a bunch of do stmts, with explicit braces and semicolons,
-- so that we are not vulnerable to layout bugs
ppr_do_stmts stmts
= lbrace <+> pprDeeperList vcat ([ppr s <> semi | s <- stmts])
= lbrace <+> pprDeeperList vcat (punctuate semi (map ppr stmts))
<+> rbrace
ppr_lc_stmts :: OutputableBndr id => [LStmt id] -> [SDoc]
......@@ -1271,6 +1289,7 @@ data HsStmtContext id
isDoExpr :: HsStmtContext id -> Bool
isDoExpr DoExpr = True
isDoExpr MDoExpr = True
isDoExpr GhciStmt = True
isDoExpr _ = False
isListCompExpr :: HsStmtContext id -> Bool
......@@ -1320,34 +1339,40 @@ pprMatchContextNoun ProcExpr = ptext (sLit "arrow abstraction")
pprMatchContextNoun (StmtCtxt ctxt) = ptext (sLit "pattern binding in")
$$ pprStmtContext ctxt