% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\begin{code}
+{-# LANGUAGE DeriveDataTypeable #-}
-- | Abstract Haskell syntax for expressions.
module HsExpr where
import SrcLoc
import Outputable
import FastString
+
+-- libraries:
+import Data.Data hiding (Fixity)
\end{code}
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
| 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
[LStmt id] -- "do":one or more stmts
(LHsExpr id) -- The body; the last expression in the
-- 'do' of [ body | ... ] in a list comp
+ (SyntaxExpr id) -- The 'return' function, see Note
+ -- [Monad Comprehensions]
PostTcType -- Type of the whole expression
| ExplicitList -- syntactic list
| HsWrap HsWrapper -- TRANSLATION
(HsExpr id)
+ deriving (Data, Typeable)
-- HsTupArg is used for tuple sections
-- (,a,) is represented by ExplicitTuple [Mising ty1, Present a, Missing ty3]
data HsTupArg id
= Present (LHsExpr id) -- The argument
| Missing PostTcType -- The argument is missing, but this is its type
+ deriving (Data, Typeable)
tupArgPresent :: HsTupArg id -> Bool
tupArgPresent (Present {}) = True
-- 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
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 body _ _) = pprDo do_or_list_comp stmts body
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
type LHsCmd id = LHsExpr id
data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp
+ deriving (Data, Typeable)
\end{code}
The legal constructors for commands are:
[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
PostTcType -- return type of the command
(SyntaxTable id) -- after type checking:
-- names used in the command's desugaring
+ deriving (Data, Typeable)
\end{code}
%************************************************************************
PostTcType -- The type is the type of the entire group
-- t1 -> ... -> tn -> tr
-- where there are n patterns
+ deriving (Data, Typeable)
type LMatch id = Located (Match id)
(Maybe (LHsType id)) -- A type signature for the result of the match
-- Nothing after typechecking
(GRHSs id)
+ deriving (Data, Typeable)
isEmptyMatchGroup :: MatchGroup id -> Bool
isEmptyMatchGroup (MatchGroup ms _) = null ms
= GRHSs {
grhssGRHSs :: [LGRHS id], -- ^ Guarded RHSs
grhssLocalBinds :: (HsLocalBinds id) -- ^ The where clause
- }
+ } deriving (Data, Typeable)
type LGRHS id = Located (GRHS id)
-- | Guarded Right Hand Side.
data GRHS id = GRHS [LStmt id] -- Guards
(LHsExpr id) -- Right hand side
+ deriving (Data, Typeable)
\end{code}
We know the list must have at least one @Match@ in it.
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)
(LHsExpr idR)
| ExprStmt (LHsExpr idR) -- See Note [ExprStmt]
(SyntaxExpr idR) -- The (>>) operator
+ (SyntaxExpr idR) -- The `guard` operator
+ -- 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])]
+ (SyntaxExpr idR) -- polymorphic `mzip` for monad comprehensions
+ (SyntaxExpr idR) -- The `>>=` operator
+ (SyntaxExpr idR) -- polymorphic `return` operator
+ -- See notes [Monad Comprehensions]
+
-- 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
+ -- "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'
(Maybe (LHsExpr idR)) -- "by e" (optional)
+ (SyntaxExpr idR) -- The 'return' function for inner monad
+ -- comprehensions
+ (SyntaxExpr idR) -- The '(>>=)' operator.
+ -- See Note [Monad Comprehensions]
+
| GroupStmt
[LStmt idL] -- Stmts to the *left* of the 'group'
-- which generates the tuples to be grouped
(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)
+
+ (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]
-- Recursive statement (see Note [How RecStmt works] below)
| RecStmt
-- because the Id may be *polymorphic*, but
-- 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
}
+ deriving (Data, Typeable)
\end{code}
Note [GroupStmt binder map]
E :: Bool
Translation: if E then fail else ...
+ A monad comprehension of type (m res_ty)
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ * ExprStmt E Bool: [ .. | .... E ]
+ E :: Bool
+ Translation: guard E >> ...
+
Array comprehensions are handled like list comprehensions -=chak
Note [How RecStmt works]
where v1..vn are the later_ids
r1..rm are the rec_ids
+Note [Monad Comprehensions]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Monad comprehensions require seperate functions like 'return' and '>>=' for
+desugaring. These functions are stored in the 'HsDo' expression and the
+statements used in monad comprehensions. For example, the 'return' of the
+'HsDo' 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 ]
+
+Normal expressions 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
pprStmt :: (OutputableBndr idL, OutputableBndr idR) => (StmtLR idL idR) -> SDoc
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 (TransformStmt stmts bndrs using by _ _)
+ = sep (ppr_lc_stmts stmts ++ [pprTransformStmt bndrs using by])
-pprStmt (GroupStmt stmts _ by using)
+pprStmt (GroupStmt stmts _ by using _ _ _)
= sep (ppr_lc_stmts stmts ++ [pprGroupStmt by using])
pprStmt (RecStmt { recS_stmts = segment, recS_rec_ids = rec_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)
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 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 MonadComp stmts body = brackets $ pprComp stmts body
pprDo _ _ _ = panic "pprDo" -- PatGuard, ParStmtCxt
ppr_do_stmts :: OutputableBndr id => [LStmt id] -> LHsExpr id -> SDoc
data HsSplice id = HsSplice -- $z or $(f 4)
id -- The id is just a unique name to
(LHsExpr id) -- identify this splice point
+ deriving (Data, Typeable)
instance OutputableBndr id => Outputable (HsSplice id) where
ppr = pprSplice
pprSplice :: OutputableBndr id => HsSplice id -> SDoc
pprSplice (HsSplice n e)
- = char '$' <> ifPprDebug (brackets (ppr n)) <> pprParendExpr e
-
+ = char '$' <> ifPprDebug (brackets (ppr n)) <> eDoc
+ where
+ -- We use pprLExpr to match pprParendExpr:
+ -- Using pprLExpr makes sure that we go 'deeper'
+ -- I think that is usually (always?) right
+ pp_as_was = pprLExpr e
+ eDoc = case unLoc e of
+ HsPar _ -> pp_as_was
+ HsVar _ -> pp_as_was
+ _ -> parens pp_as_was
data HsBracket id = ExpBr (LHsExpr id) -- [| expr |]
| PatBr (LPat id) -- [p| pat |]
| DecBrG (HsGroup id) -- [d| decls |]; result of renamer
| TypBr (LHsType id) -- [t| type |]
| VarBr id -- 'x, ''T
+ deriving (Data, Typeable)
instance OutputableBndr id => Outputable (HsBracket id) where
ppr = pprHsBracket
| FromThenTo (LHsExpr id)
(LHsExpr id)
(LHsExpr id)
+ deriving (Data, Typeable)
\end{code}
\begin{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 ()
+ 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)
+ | MDoExpr -- Recursive do-expression
+ | MonadComp
| PArrComp -- Parallel array comprehension
| 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
+ deriving (Data, Typeable)
\end{code}
\begin{code}
isDoExpr :: HsStmtContext id -> Bool
-isDoExpr DoExpr = True
-isDoExpr (MDoExpr _) = True
-isDoExpr _ = False
+isDoExpr DoExpr = True
+isDoExpr MDoExpr = True
+isDoExpr _ = False
isListCompExpr :: HsStmtContext id -> Bool
-isListCompExpr ListComp = True
-isListCompExpr PArrComp = True
-isListCompExpr _ = False
+isListCompExpr ListComp = True
+isListCompExpr PArrComp = True
+isListCompExpr MonadComp = True
+isListCompExpr _ = False
+
+isMonadCompExpr :: HsStmtContext id -> Bool
+isMonadCompExpr MonadComp = True
+isMonadCompExpr (ParStmtCtxt ctxt) = isMonadCompExpr ctxt
+isMonadCompExpr (TransformStmtCtxt 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")
- $$ pprStmtContext ctxt
+pprMatchContext ctxt
+ | want_an ctxt = ptext (sLit "an") <+> pprMatchContextNoun ctxt
+ | otherwise = ptext (sLit "a") <+> pprMatchContextNoun ctxt
+ where
+ want_an (FunRhs {}) = True -- Use "an" in front
+ want_an ProcExpr = True
+ want_an _ = False
+
+pprMatchContextNoun :: Outputable id => HsMatchContext id -> SDoc
+pprMatchContextNoun (FunRhs fun _) = ptext (sLit "equation for")
+ <+> quotes (ppr fun)
+pprMatchContextNoun CaseAlt = ptext (sLit "case alternative")
+pprMatchContextNoun RecUpd = ptext (sLit "record-update construct")
+pprMatchContextNoun ThPatQuote = ptext (sLit "Template Haskell pattern quotation")
+pprMatchContextNoun PatBindRhs = ptext (sLit "pattern binding")
+pprMatchContextNoun LambdaExpr = ptext (sLit "lambda abstraction")
+pprMatchContextNoun ProcExpr = ptext (sLit "arrow abstraction")
+pprMatchContextNoun (StmtCtxt ctxt) = ptext (sLit "pattern binding in")
+ $$ pprStmtContext ctxt
pprStmtContext :: Outputable id => HsStmtContext id -> SDoc
pprStmtContext (ParStmtCtxt c)
= 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 MDoExpr = ptext (sLit "an 'mdo' expression")
pprStmtContext ListComp = ptext (sLit "a list comprehension")
+pprStmtContext MonadComp = ptext (sLit "a monad comprehension")
pprStmtContext PArrComp = ptext (sLit "an array comprehension")
{-
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 MDoExpr) = ptext (sLit "'mdo' expression")
matchContextErrString (StmtCtxt ListComp) = ptext (sLit "list comprehension")
+matchContextErrString (StmtCtxt MonadComp) = ptext (sLit "monad comprehension")
matchContextErrString (StmtCtxt PArrComp) = ptext (sLit "array comprehension")
\end{code}
4 (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 (GroupStmt _ _ by using _ _ _) = pprGroupStmt by using
+ ppr_stmt (TransformStmt _ bndrs using by _ _) = pprTransformStmt bndrs using by
+ ppr_stmt stmt = pprStmt stmt
\end{code}
projects / ghc-hetmet.git / blobdiff