import BasicTypes
import DataCon
import SrcLoc
+import Util( dropTail )
+import StaticFlags( opt_PprStyle_Debug )
import Outputable
import FastString
type PostTcExpr = HsExpr Id
-- | We use a PostTcTable where there are a bunch of pieces of evidence, more
-- than is convenient to keep individually.
-type PostTcTable = [(Name, Id)]
+type PostTcTable = [(Name, PostTcExpr)]
noPostTcExpr :: PostTcExpr
noPostTcExpr = HsLit (HsString (fsLit "noPostTcExpr"))
--
-- E.g. @(>>=)@ is filled in before the renamer by the appropriate 'Name' for
-- @(>>=)@, and then instantiated by the type checker with its type args
--- tec
+-- etc
type SyntaxExpr id = HsExpr id
| HsApp (LHsExpr id) (LHsExpr id) -- Application
+ | HsKappa (MatchGroup id)
+
+ | HsKappaApp (LHsExpr id) (LHsExpr id)
+
-- Operator applications:
-- NB Bracketed ops such as (+) come out as Vars.
| HsCase (LHsExpr id)
(MatchGroup id)
- | HsIf (LHsExpr id) -- predicate
+ | HsIf (Maybe (SyntaxExpr id)) -- cond function
+ -- Nothing => use the built-in 'if'
+ -- See Note [Rebindable if]
+ (LHsExpr id) -- predicate
(LHsExpr id) -- then part
(LHsExpr id) -- else part
-- because in this context we never use
-- the PatGuard or ParStmt variant
[LStmt id] -- "do":one or more stmts
- (LHsExpr id) -- The body; the last expression in the
- -- 'do' of [ body | ... ] in a list comp
PostTcType -- Type of the whole expression
| ExplicitList -- syntactic list
(LHsCmdTop id) -- body of the abstraction
-- always has an empty stack
+ -----------------------------------------------------------
+ -- Heterogeneous Metaprogramming extension
+
+ | HsHetMetBrak PostTcType (LHsExpr id) -- code type brackets
+ | HsHetMetEsc PostTcType PostTcType (LHsExpr id) -- code type escape
+ | HsHetMetCSP PostTcType (LHsExpr id) -- code type cross-stage persistence
+
---------------------------------------
-- The following are commands, not expressions proper
-- pasted back in by the desugarer
\end{code}
-A @Dictionary@, unless of length 0 or 1, becomes a tuple. A
-@ClassDictLam dictvars methods expr@ is, therefore:
-\begin{verbatim}
-\ x -> case x of ( dictvars-and-methods-tuple ) -> expr
-\end{verbatim}
+Note [Rebindable if]
+~~~~~~~~~~~~~~~~~~~~
+The rebindable syntax for 'if' is a bit special, because when
+rebindable syntax is *off* we do not want to treat
+ (if c then t else e)
+as if it was an application (ifThenElse c t e). Why not?
+Because we allow an 'if' to return *unboxed* results, thus
+ if blah then 3# else 4#
+whereas that would not be possible using a all to a polymorphic function
+(because you can't call a polymorphic function at an unboxed type).
+
+So we use Nothing to mean "use the old built-in typing rule".
\begin{code}
instance OutputableBndr id => Outputable (HsExpr id) where
ppr_expr (HsLit lit) = ppr lit
ppr_expr (HsOverLit lit) = ppr lit
ppr_expr (HsPar e) = parens (ppr_lexpr e)
+ppr_expr (HsHetMetBrak _ e) = ptext (sLit "<[") <> (ppr_lexpr e) <> ptext (sLit "]>")
+ppr_expr (HsHetMetEsc _ _ e) = ptext (sLit "~~") <> (ppr_lexpr e)
+ppr_expr (HsHetMetCSP _ e) = ptext (sLit "%%") <> (ppr_lexpr e)
ppr_expr (HsCoreAnn s e)
= vcat [ptext (sLit "HsCoreAnn") <+> ftext s, ppr_lexpr e]
+ppr_expr (HsKappaApp e1 e2) = ppr_expr $ HsApp e1 e2
+ppr_expr (HsKappa e) = ppr_expr $ HsLam e
ppr_expr (HsApp e1 e2)
= let (fun, args) = collect_args e1 [e2] in
hang (ppr_lexpr fun) 2 (sep (map pprParendExpr args))
nest 2 (pprMatches (CaseAlt `asTypeOf` idType exprType) matches <+> char '}') ]
where idType :: HsExpr id -> HsMatchContext id; idType = undefined
-ppr_expr (HsIf e1 e2 e3)
+ppr_expr (HsIf _ e1 e2 e3)
= sep [hsep [ptext (sLit "if"), nest 2 (ppr e1), ptext (sLit "then")],
nest 4 (ppr e2),
ptext (sLit "else"),
= sep [hang (ptext (sLit "let")) 2 (pprBinds binds),
hang (ptext (sLit "in")) 2 (ppr expr)]
-ppr_expr (HsDo do_or_list_comp stmts body _) = pprDo do_or_list_comp stmts body
+ppr_expr (HsDo do_or_list_comp stmts _) = pprDo do_or_list_comp stmts
ppr_expr (ExplicitList _ exprs)
= brackets (pprDeeperList fsep (punctuate comma (map ppr_lexpr exprs)))
HsPar {} -> pp_as_was
HsBracket {} -> pp_as_was
HsBracketOut _ [] -> pp_as_was
- HsDo sc _ _ _
+ HsDo sc _ _
| isListCompExpr sc -> pp_as_was
_ -> parens pp_as_was
[Match id] -- bodies are HsCmd's
SrcLoc
- | HsIf (HsExpr id) -- predicate
+ | HsIf (Maybe (SyntaxExpr id)) -- cond function
+ (HsExpr id) -- predicate
(HsCmd id) -- then part
(HsCmd id) -- else part
SrcLoc
pprPatBind :: (OutputableBndr bndr, OutputableBndr id)
=> LPat bndr -> GRHSs id -> SDoc
pprPatBind pat ty@(grhss)
- = sep [ppr pat, nest 4 (pprGRHSs (PatBindRhs `asTypeOf` idType ty) grhss)]
+ = sep [ppr pat, nest 2 (pprGRHSs (PatBindRhs `asTypeOf` idType ty) grhss)]
--avoid using PatternSignatures for stage1 code portability
where idType :: GRHSs id -> HsMatchContext id; idType = undefined
pprMatch :: (OutputableBndr idL, OutputableBndr idR) => HsMatchContext idL -> Match idR -> SDoc
pprMatch ctxt (Match pats maybe_ty grhss)
- = herald <+> sep [sep (map pprParendLPat other_pats),
- ppr_maybe_ty,
- nest 2 (pprGRHSs ctxt grhss)]
+ = sep [ sep (herald : map (nest 2 . pprParendLPat) other_pats)
+ , nest 2 ppr_maybe_ty
+ , nest 2 (pprGRHSs ctxt grhss) ]
where
(herald, other_pats)
= case ctxt of
type Stmt id = StmtLR id id
--- The SyntaxExprs in here are used *only* for do-notation, which
--- has rebindable syntax. Otherwise they are unused.
+-- The SyntaxExprs in here are used *only* for do-notation and monad
+-- comprehensions, which have rebindable syntax. Otherwise they are unused.
data StmtLR idL idR
- = BindStmt (LPat idL)
+ = LastStmt -- Always the last Stmt in ListComp, MonadComp, PArrComp,
+ -- and (after the renamer) DoExpr, MDoExpr
+ -- 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; used only in MonadComp
+ -- See notes [Monad Comprehensions]
PostTcType -- Element type of the RHS (used for arrows)
| LetStmt (HsLocalBindsLR idL idR)
- -- ParStmts only occur in a list comprehension
+ -- ParStmts only occur in a list/monad comprehension
| ParStmt [([LStmt idL], [idR])]
- -- 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)
- -- "qs, then f" ==> TransformStmt qs binders f Nothing
- | TransformStmt
- [LStmt idL] -- Stmts are the ones to the left of the 'then'
-
- [idR] -- After renaming, the IDs are the binders occurring
- -- within this transform statement that are used after it
-
- (LHsExpr idR) -- "then f"
-
- (Maybe (LHsExpr idR)) -- "by e" (optional)
-
- | GroupStmt
- [LStmt idL] -- Stmts to the *left* of the 'group'
- -- which generates the tuples to be grouped
-
- [(idR, idR)] -- See Note [GroupStmt binder map]
+ (SyntaxExpr idR) -- Polymorphic `mzip` for monad comprehensions
+ (SyntaxExpr idR) -- The `>>=` operator
+ (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 themp
+
+ | TransStmt {
+ trS_form :: TransForm,
+ trS_stmts :: [LStmt idL], -- Stmts to the *left* of the 'group'
+ -- which generates the tuples to be grouped
+
+ trS_bndrs :: [(idR, idR)], -- See Note [TransStmt binder map]
- (Maybe (LHsExpr idR)) -- "by e" (optional)
+ trS_using :: LHsExpr idR,
+ trS_by :: Maybe (LHsExpr idR), -- "by e" (optional)
+ -- Invariant: if trS_form = GroupBy, then grp_by = Just e
- (Either -- "using f"
- (LHsExpr idR) -- Left f => explicit "using f"
- (SyntaxExpr idR)) -- Right f => implicit; filled in with 'groupWith'
-
+ trS_ret :: SyntaxExpr idR, -- The monomorphic 'return' function for
+ -- the inner monad comprehensions
+ trS_bind :: SyntaxExpr idR, -- The '(>>=)' operator
+ trS_fmap :: SyntaxExpr idR -- The polymorphic 'fmap' function for desugaring
+ -- Only for 'group' forms
+ } -- See Note [Monad Comprehensions]
-- Recursive statement (see Note [How RecStmt works] below)
| RecStmt
-- the returned thing has to be *monomorphic*,
-- so they may be type applications
- , recS_dicts :: DictBinds idR -- Method bindings of Ids bound by the
- -- RecStmt, and used afterwards
+ , recS_ret_ty :: PostTcType -- The type of of do { stmts; return (a,b,c) }
+ -- With rebindable syntax the type might not
+ -- be quite as simple as (m (tya, tyb, tyc)).
}
deriving (Data, Typeable)
+
+data TransForm -- The 'f' below is the 'using' function, 'e' is the by function
+ = ThenForm -- then f or then f by e
+ | GroupFormU -- group using f or group using f by e
+ | GroupFormB -- group by e
+ -- In the GroupByFormB, trS_using is filled in with
+ -- 'groupWith' (list comprehensions) or
+ -- 'groupM' (monad comprehensions)
+ deriving (Data, Typeable)
\end{code}
-Note [GroupStmt binder map]
+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 [TransStmt binder map]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
-The [(idR,idR)] in a GroupStmt behaves as follows:
+The [(idR,idR)] in a TransStmt behaves as follows:
* Before renaming: []
* After renaming:
[ (x27,x27), ..., (z35,z35) ]
These are the variables
- bound by the stmts to the left of the 'group'
+ bound by the stmts to the left of the 'group'
and used either in the 'by' clause,
or in the stmts following the 'group'
Each item is a pair of identical variables.
E :: Bool
Translation: if E then fail else ...
-Array comprehensions are handled like list comprehensions -=chak
+ A monad comprehension of type (m res_ty)
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ * ExprStmt E Bool: [ .. | .... E ]
+ E :: Bool
+ Translation: guard E >> ...
+
+Array comprehensions are handled like list comprehensions.
Note [How RecStmt works]
~~~~~~~~~~~~~~~~~~~~~~~~
where v1..vn are the later_ids
r1..rm are the rec_ids
+Note [Monad Comprehensions]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Monad comprehensions require separate functions like 'return' and
+'>>=' for desugaring. These functions are stored in the statements
+used in monad comprehensions. For example, the 'return' of the 'LastStmt'
+expression is used to lift the body of the monad comprehension:
+
+ [ body | stmts ]
+ =>
+ stmts >>= \bndrs -> return body
+
+In transform and grouping statements ('then ..' and 'then group ..') the
+'return' function is required for nested monad comprehensions, for example:
+
+ [ body | stmts, then f, rest ]
+ =>
+ f [ env | stmts ] >>= \bndrs -> [ body | rest ]
+
+ExprStmts require the 'Control.Monad.guard' function for boolean
+expressions:
+
+ [ body | exp, stmts ]
+ =>
+ guard exp >> [ body | stmts ]
+
+Grouping/parallel statements require the 'Control.Monad.Group.groupM' and
+'Control.Monad.Zip.mzip' functions:
+
+ [ body | stmts, then group by e, rest]
+ =>
+ groupM [ body | stmts ] >>= \bndrs -> [ body | rest ]
+
+ [ body | stmts1 | stmts2 | .. ]
+ =>
+ mzip stmts1 (mzip stmts2 (..)) >>= \(bndrs1, (bndrs2, ..)) -> return body
+
+In any other context than 'MonadComp', the fields for most of these
+'SyntaxExpr's stay bottom.
+
\begin{code}
instance (OutputableBndr idL, OutputableBndr idR) => Outputable (StmtLR idL idR) where
ppr stmt = pprStmt stmt
pprStmt :: (OutputableBndr idL, OutputableBndr idR) => (StmtLR idL idR) -> SDoc
+pprStmt (LastStmt expr _) = ifPprDebug (ptext (sLit "[last]")) <+> ppr expr
pprStmt (BindStmt pat expr _ _) = hsep [ppr pat, ptext (sLit "<-"), ppr expr]
pprStmt (LetStmt binds) = hsep [ptext (sLit "let"), pprBinds binds]
-pprStmt (ExprStmt expr _ _) = ppr expr
-pprStmt (ParStmt stmtss) = hsep (map doStmts stmtss)
+pprStmt (ExprStmt expr _ _ _) = ppr expr
+pprStmt (ParStmt stmtss _ _ _) = hsep (map doStmts stmtss)
where doStmts stmts = ptext (sLit "| ") <> ppr stmts
-pprStmt (TransformStmt stmts _ using by)
- = sep (ppr_lc_stmts stmts ++ [pprTransformStmt using by])
-
-pprStmt (GroupStmt stmts _ by using)
- = sep (ppr_lc_stmts stmts ++ [pprGroupStmt by using])
+pprStmt (TransStmt { trS_stmts = stmts, trS_by = by, trS_using = using, trS_form = form })
+ = sep (ppr_lc_stmts stmts ++ [pprTransStmt by using form])
pprStmt (RecStmt { recS_stmts = segment, recS_rec_ids = rec_ids
, recS_later_ids = later_ids })
, ifPprDebug (vcat [ ptext (sLit "rec_ids=") <> ppr rec_ids
, ptext (sLit "later_ids=") <> ppr later_ids])]
-pprTransformStmt :: OutputableBndr id => LHsExpr id -> Maybe (LHsExpr id) -> SDoc
-pprTransformStmt using by = sep [ ptext (sLit "then"), nest 2 (ppr using), nest 2 (pprBy by)]
+pprTransformStmt :: OutputableBndr id => [id] -> LHsExpr id -> Maybe (LHsExpr id) -> SDoc
+pprTransformStmt bndrs using by
+ = sep [ ptext (sLit "then") <+> ifPprDebug (braces (ppr bndrs))
+ , nest 2 (ppr using)
+ , nest 2 (pprBy by)]
-pprGroupStmt :: OutputableBndr id => Maybe (LHsExpr id)
- -> Either (LHsExpr id) (SyntaxExpr is)
+pprTransStmt :: OutputableBndr id => Maybe (LHsExpr id)
+ -> LHsExpr id -> TransForm
-> SDoc
-pprGroupStmt by using
- = sep [ ptext (sLit "then group"), nest 2 (pprBy by), nest 2 (ppr_using using)]
- where
- ppr_using (Right _) = empty
- ppr_using (Left e) = ptext (sLit "using") <+> ppr e
+pprTransStmt by using ThenForm
+ = sep [ ptext (sLit "then"), nest 2 (ppr using), nest 2 (pprBy by)]
+pprTransStmt by _ GroupFormB
+ = sep [ ptext (sLit "then group"), nest 2 (pprBy by) ]
+pprTransStmt by using GroupFormU
+ = sep [ ptext (sLit "then group"), nest 2 (pprBy by), nest 2 (ptext (sLit "using") <+> ppr using)]
pprBy :: OutputableBndr id => Maybe (LHsExpr id) -> SDoc
pprBy Nothing = empty
pprBy (Just e) = ptext (sLit "by") <+> ppr e
-pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> LHsExpr id -> SDoc
-pprDo DoExpr stmts body = ptext (sLit "do") <+> ppr_do_stmts stmts body
-pprDo GhciStmt stmts body = ptext (sLit "do") <+> ppr_do_stmts stmts body
-pprDo (MDoExpr _) stmts body = ptext (sLit "mdo") <+> ppr_do_stmts stmts body
-pprDo ListComp stmts body = brackets $ pprComp stmts body
-pprDo PArrComp stmts body = pa_brackets $ pprComp stmts body
-pprDo _ _ _ = panic "pprDo" -- PatGuard, ParStmtCxt
-
-ppr_do_stmts :: OutputableBndr id => [LStmt id] -> LHsExpr id -> SDoc
+pprDo :: OutputableBndr id => HsStmtContext any -> [LStmt id] -> SDoc
+pprDo DoExpr stmts = ptext (sLit "do") <+> ppr_do_stmts stmts
+pprDo GhciStmt stmts = ptext (sLit "do") <+> ppr_do_stmts stmts
+pprDo ArrowExpr stmts = ptext (sLit "do") <+> ppr_do_stmts stmts
+pprDo MDoExpr stmts = ptext (sLit "mdo") <+> ppr_do_stmts stmts
+pprDo ListComp stmts = brackets $ pprComp stmts
+pprDo PArrComp stmts = pa_brackets $ pprComp stmts
+pprDo MonadComp stmts = brackets $ pprComp stmts
+pprDo _ _ = panic "pprDo" -- PatGuard, ParStmtCxt
+
+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 body
- = lbrace <+> pprDeeperList vcat ([ppr s <> semi | s <- stmts] ++ [ppr body])
+ppr_do_stmts stmts
+ = lbrace <+> pprDeeperList vcat (punctuate semi (map ppr stmts))
<+> rbrace
ppr_lc_stmts :: OutputableBndr id => [LStmt id] -> [SDoc]
ppr_lc_stmts stmts = [ppr s <> comma | s <- stmts]
-pprComp :: OutputableBndr id => [LStmt id] -> LHsExpr id -> SDoc
-pprComp quals body -- Prints: body | qual1, ..., qualn
- = hang (ppr body <+> char '|') 2 (interpp'SP quals)
+pprComp :: OutputableBndr id => [LStmt id] -> SDoc
+pprComp quals -- Prints: body | qual1, ..., qualn
+ | not (null quals)
+ , L _ (LastStmt body _) <- last quals
+ = hang (ppr body <+> char '|') 2 (interpp'SP (dropTail 1 quals))
+ | otherwise
+ = pprPanic "pprComp" (interpp'SP quals)
\end{code}
%************************************************************************
\begin{code}
data HsMatchContext id -- Context of a Match
= FunRhs id Bool -- Function binding for f; True <=> written infix
- | CaseAlt -- Patterns and guards on a case alternative
| LambdaExpr -- Patterns of a lambda
+ | CaseAlt -- Patterns and guards on a case alternative
| ProcExpr -- Patterns of a proc
- | PatBindRhs -- Patterns in the *guards* of a pattern binding
+ | PatBindRhs -- A pattern binding eg [y] <- e = e
+
| RecUpd -- Record update [used only in DsExpr to
-- tell matchWrapper what sort of
-- runtime error message to generate]
- | StmtCtxt (HsStmtContext id) -- Pattern of a do-stmt or list comprehension
+
+ | StmtCtxt (HsStmtContext id) -- Pattern of a do-stmt, list comprehension,
+ -- pattern guard, etc
+
| ThPatQuote -- A Template Haskell pattern quotation [p| (a,b) |]
deriving (Data, Typeable)
data HsStmtContext id
= ListComp
- | DoExpr
- | GhciStmt -- A command-line Stmt in GHCi pat <- rhs
- | MDoExpr PostTcTable -- Recursive do-expression
- -- (tiresomely, it needs table
- -- of its return/bind ops)
+ | MonadComp
| PArrComp -- Parallel array comprehension
+
+ | DoExpr -- do { ... }
+ | MDoExpr -- mdo { ... } ie recursive do-expression
+ | ArrowExpr -- do-notation in an arrow-command context
+
+ | GhciStmt -- A command-line Stmt in GHCi pat <- rhs
| PatGuard (HsMatchContext id) -- Pattern guard for specified thing
| ParStmtCtxt (HsStmtContext id) -- A branch of a parallel stmt
- | TransformStmtCtxt (HsStmtContext id) -- A branch of a transform stmt
+ | TransStmtCtxt (HsStmtContext id) -- A branch of a transform stmt
deriving (Data, Typeable)
\end{code}
\begin{code}
-isDoExpr :: HsStmtContext id -> Bool
-isDoExpr DoExpr = True
-isDoExpr (MDoExpr _) = True
-isDoExpr _ = False
-
isListCompExpr :: HsStmtContext id -> Bool
-isListCompExpr ListComp = True
-isListCompExpr PArrComp = True
-isListCompExpr _ = False
+-- Uses syntax [ e | quals ]
+isListCompExpr ListComp = True
+isListCompExpr PArrComp = True
+isListCompExpr MonadComp = True
+isListCompExpr (ParStmtCtxt c) = isListCompExpr c
+isListCompExpr (TransStmtCtxt c) = isListCompExpr c
+isListCompExpr _ = False
+
+isMonadCompExpr :: HsStmtContext id -> Bool
+isMonadCompExpr MonadComp = True
+isMonadCompExpr (ParStmtCtxt ctxt) = isMonadCompExpr ctxt
+isMonadCompExpr (TransStmtCtxt ctxt) = isMonadCompExpr ctxt
+isMonadCompExpr _ = False
\end{code}
\begin{code}
\begin{code}
pprMatchContext :: Outputable id => HsMatchContext id -> SDoc
-pprMatchContext (FunRhs fun _) = ptext (sLit "the definition of")
- <+> quotes (ppr fun)
-pprMatchContext CaseAlt = ptext (sLit "a case alternative")
-pprMatchContext RecUpd = ptext (sLit "a record-update construct")
-pprMatchContext ThPatQuote = ptext (sLit "a Template Haskell pattern quotation")
-pprMatchContext PatBindRhs = ptext (sLit "a pattern binding")
-pprMatchContext LambdaExpr = ptext (sLit "a lambda abstraction")
-pprMatchContext ProcExpr = ptext (sLit "an arrow abstraction")
-pprMatchContext (StmtCtxt ctxt) = ptext (sLit "a pattern binding in")
- $$ pprStmtContext ctxt
-
-pprStmtContext :: Outputable id => HsStmtContext id -> SDoc
+pprMatchContext ctxt
+ | want_an ctxt = ptext (sLit "an") <+> pprMatchContextNoun ctxt
+ | otherwise = ptext (sLit "a") <+> pprMatchContextNoun ctxt
+ where
+ want_an (FunRhs {}) = True -- Use "an" in front
+ want_an ProcExpr = True
+ want_an _ = False
+
+pprMatchContextNoun :: Outputable id => HsMatchContext id -> SDoc
+pprMatchContextNoun (FunRhs fun _) = ptext (sLit "equation for")
+ <+> quotes (ppr fun)
+pprMatchContextNoun CaseAlt = ptext (sLit "case alternative")
+pprMatchContextNoun RecUpd = ptext (sLit "record-update construct")
+pprMatchContextNoun ThPatQuote = ptext (sLit "Template Haskell pattern quotation")
+pprMatchContextNoun PatBindRhs = ptext (sLit "pattern binding")
+pprMatchContextNoun LambdaExpr = ptext (sLit "lambda abstraction")
+pprMatchContextNoun ProcExpr = ptext (sLit "arrow abstraction")
+pprMatchContextNoun (StmtCtxt ctxt) = ptext (sLit "pattern binding in")
+ $$ pprStmtContext ctxt
+
+-----------------
+pprAStmtContext, pprStmtContext :: Outputable id => HsStmtContext id -> SDoc
+pprAStmtContext ctxt = article <+> pprStmtContext ctxt
+ where
+ pp_an = ptext (sLit "an")
+ pp_a = ptext (sLit "a")
+ article = case ctxt of
+ MDoExpr -> pp_an
+ PArrComp -> pp_an
+ GhciStmt -> pp_an
+ _ -> pp_a
+
+
+-----------------
+pprStmtContext GhciStmt = ptext (sLit "interactive GHCi command")
+pprStmtContext DoExpr = ptext (sLit "'do' block")
+pprStmtContext MDoExpr = ptext (sLit "'mdo' block")
+pprStmtContext ArrowExpr = ptext (sLit "'do' block in an arrow command")
+pprStmtContext ListComp = ptext (sLit "list comprehension")
+pprStmtContext MonadComp = ptext (sLit "monad comprehension")
+pprStmtContext PArrComp = ptext (sLit "array comprehension")
+pprStmtContext (PatGuard ctxt) = ptext (sLit "pattern guard for") $$ pprMatchContext ctxt
+
+-- Drop the inner contexts when reporting errors, else we get
+-- Unexpected transform statement
+-- in a transformed branch of
+-- transformed branch of
+-- transformed branch of monad comprehension
pprStmtContext (ParStmtCtxt c)
- = sep [ptext (sLit "a parallel branch of"), pprStmtContext c]
-pprStmtContext (TransformStmtCtxt c)
- = sep [ptext (sLit "a transformed branch of"), pprStmtContext c]
-pprStmtContext (PatGuard ctxt)
- = ptext (sLit "a pattern guard for") $$ pprMatchContext ctxt
-pprStmtContext GhciStmt = ptext (sLit "an interactive GHCi command")
-pprStmtContext DoExpr = ptext (sLit "a 'do' expression")
-pprStmtContext (MDoExpr _) = ptext (sLit "an 'mdo' expression")
-pprStmtContext ListComp = ptext (sLit "a list comprehension")
-pprStmtContext PArrComp = ptext (sLit "an array comprehension")
-
-{-
-pprMatchRhsContext (FunRhs fun) = ptext (sLit "a right-hand side of function") <+> quotes (ppr fun)
-pprMatchRhsContext CaseAlt = ptext (sLit "the body of a case alternative")
-pprMatchRhsContext PatBindRhs = ptext (sLit "the right-hand side of a pattern binding")
-pprMatchRhsContext LambdaExpr = ptext (sLit "the body of a lambda")
-pprMatchRhsContext ProcExpr = ptext (sLit "the body of a proc")
-pprMatchRhsContext other = panic "pprMatchRhsContext" -- RecUpd, StmtCtxt
-
--- Used for the result statement of comprehension
--- e.g. the 'e' in [ e | ... ]
--- or the 'r' in f x = r
-pprStmtResultContext (PatGuard ctxt) = pprMatchRhsContext ctxt
-pprStmtResultContext other = ptext (sLit "the result of") <+> pprStmtContext other
--}
+ | opt_PprStyle_Debug = sep [ptext (sLit "parallel branch of"), pprAStmtContext c]
+ | otherwise = pprStmtContext c
+pprStmtContext (TransStmtCtxt c)
+ | opt_PprStyle_Debug = sep [ptext (sLit "transformed branch of"), pprAStmtContext c]
+ | otherwise = pprStmtContext c
+
-- Used to generate the string for a *runtime* error message
matchContextErrString :: Outputable id => HsMatchContext id -> SDoc
matchContextErrString LambdaExpr = ptext (sLit "lambda")
matchContextErrString ProcExpr = ptext (sLit "proc")
matchContextErrString ThPatQuote = panic "matchContextErrString" -- Not used at runtime
-matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c)
-matchContextErrString (StmtCtxt (TransformStmtCtxt c)) = matchContextErrString (StmtCtxt c)
-matchContextErrString (StmtCtxt (PatGuard _)) = ptext (sLit "pattern guard")
-matchContextErrString (StmtCtxt GhciStmt) = ptext (sLit "interactive GHCi command")
-matchContextErrString (StmtCtxt DoExpr) = ptext (sLit "'do' expression")
-matchContextErrString (StmtCtxt (MDoExpr _)) = ptext (sLit "'mdo' expression")
-matchContextErrString (StmtCtxt ListComp) = ptext (sLit "list comprehension")
-matchContextErrString (StmtCtxt PArrComp) = ptext (sLit "array comprehension")
+matchContextErrString (StmtCtxt (ParStmtCtxt c)) = matchContextErrString (StmtCtxt c)
+matchContextErrString (StmtCtxt (TransStmtCtxt c)) = matchContextErrString (StmtCtxt c)
+matchContextErrString (StmtCtxt (PatGuard _)) = ptext (sLit "pattern guard")
+matchContextErrString (StmtCtxt GhciStmt) = ptext (sLit "interactive GHCi command")
+matchContextErrString (StmtCtxt DoExpr) = ptext (sLit "'do' block")
+matchContextErrString (StmtCtxt ArrowExpr) = ptext (sLit "'do' block")
+matchContextErrString (StmtCtxt MDoExpr) = ptext (sLit "'mdo' block")
+matchContextErrString (StmtCtxt ListComp) = ptext (sLit "list comprehension")
+matchContextErrString (StmtCtxt MonadComp) = ptext (sLit "monad comprehension")
+matchContextErrString (StmtCtxt PArrComp) = ptext (sLit "array comprehension")
\end{code}
\begin{code}
pprStmtInCtxt :: (OutputableBndr idL, OutputableBndr idR)
=> HsStmtContext idL -> StmtLR idL idR -> SDoc
-pprStmtInCtxt ctxt stmt = hang (ptext (sLit "In a stmt of") <+> pprStmtContext ctxt <> colon)
- 4 (ppr_stmt stmt)
+pprStmtInCtxt ctxt (LastStmt e _)
+ | isListCompExpr ctxt -- For [ e | .. ], do not mutter about "stmts"
+ = hang (ptext (sLit "In the expression:")) 2 (ppr e)
+
+pprStmtInCtxt ctxt stmt
+ = hang (ptext (sLit "In a stmt of") <+> pprAStmtContext ctxt <> colon)
+ 2 (ppr_stmt stmt)
where
-- For Group and Transform Stmts, don't print the nested stmts!
- ppr_stmt (GroupStmt _ _ by using) = pprGroupStmt by using
- ppr_stmt (TransformStmt _ _ using by) = pprTransformStmt using by
- ppr_stmt stmt = pprStmt stmt
+ ppr_stmt (TransStmt { trS_by = by, trS_using = using
+ , trS_form = form }) = pprTransStmt by using form
+ ppr_stmt stmt = pprStmt stmt
\end{code}
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