hsSyn/HsBinds.lhs

% % (c) The University of Glasgow 2006 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % \section[HsBinds]{Abstract syntax: top-level bindings and signatures} Datatype for: @BindGroup@, @Bind@, @Sig@, @Bind@. \begin{code}

    {-# LANGUAGE DeriveDataTypeable #-}

    module HsBinds where

    import {-# SOURCE #-} HsExpr ( pprExpr, LHsExpr,
                                   MatchGroup, pprFunBind,
                                   GRHSs, pprPatBind )
    import {-# SOURCE #-} HsPat  ( LPat )

    import HsLit
    import HsTypes
    import PprCore ()
    import CoreSyn
    import TcEvidence
    import Type
    import Name
    import NameSet
    import BasicTypes
    import Outputable
    import SrcLoc
    import Var
    import Bag
    import FastString
    import BooleanFormula (BooleanFormula)

    import Data.Data hiding ( Fixity )
    import Data.List
    import Data.Ord
    import Data.Foldable ( Foldable(..) )
    import Data.Traversable ( Traversable(..) )
    import Data.Monoid ( mappend )
    import Control.Applicative ( (<$>), (<*>) )

\end{code} %************************************************************************ %* * \subsection{Bindings: @BindGroup@} %* * %************************************************************************ Global bindings (where clauses) \begin{code}

    -- During renaming, we need bindings where the left-hand sides
    -- have been renamed but the the right-hand sides have not.
    -- the ...LR datatypes are parametrized by two id types,
    -- one for the left and one for the right.
    -- Other than during renaming, these will be the same.

    type HsLocalBinds id = HsLocalBindsLR id id

    -- | Bindings in a 'let' expression
    -- or a 'where' clause
    data HsLocalBindsLR idL idR
      = HsValBinds (HsValBindsLR idL idR)
      | HsIPBinds  (HsIPBinds idR)
      | EmptyLocalBinds
      deriving (Data, Typeable)

    type HsValBinds id = HsValBindsLR id id

    -- | Value bindings (not implicit parameters)
    data HsValBindsLR idL idR
      = -- | Before renaming RHS; idR is always RdrName
        -- Not dependency analysed
        -- Recursive by default
        ValBindsIn
            (LHsBindsLR idL idR) [LSig idR]

        -- | After renaming RHS; idR can be Name or Id
        --  Dependency analysed,
        -- later bindings in the list may depend on earlier
        -- ones.
      | ValBindsOut
            [(RecFlag, LHsBinds idL)]
            [LSig Name]
      deriving (Data, Typeable)

    type LHsBind  id = LHsBindLR  id id
    type LHsBinds id = LHsBindsLR id id
    type HsBind   id = HsBindLR   id id

    type LHsBindsLR idL idR = Bag (LHsBindLR idL idR)
    type LHsBindLR  idL idR = Located (HsBindLR idL idR)

    data HsBindLR idL idR
      = -- | FunBind is used for both functions   @f x = e@
        -- and variables                          @f = \x -> e@
        --
        -- Reason 1: Special case for type inference: see 'TcBinds.tcMonoBinds'.
        --
        -- Reason 2: Instance decls can only have FunBinds, which is convenient.
        --           If you change this, you'll need to change e.g. rnMethodBinds
        --
        -- But note that the form                 @f :: a->a = ...@
        -- parses as a pattern binding, just like
        --                                        @(f :: a -> a) = ... @
        FunBind {

            fun_id :: Located idL,

            fun_infix :: Bool,      -- ^ True => infix declaration

            fun_matches :: MatchGroup idR (LHsExpr idR),  -- ^ The payload

            fun_co_fn :: HsWrapper, -- ^ Coercion from the type of the MatchGroup to the type of
                                    -- the Id.  Example:
                                    -- @
                                    --      f :: Int -> forall a. a -> a
                                    --      f x y = y
                                    -- @
                                    -- Then the MatchGroup will have type (Int -> a' -> a')
                                    -- (with a free type variable a').  The coercion will take
                                    -- a CoreExpr of this type and convert it to a CoreExpr of
                                    -- type         Int -> forall a'. a' -> a'
                                    -- Notice that the coercion captures the free a'.

            bind_fvs :: NameSet,    -- ^ After the renamer, this contains the locally-bound
                                    -- free variables of this defn.
                                    -- See Note [Bind free vars]

            fun_tick :: Maybe (Tickish Id)  -- ^ Tick to put on the rhs, if any
        }

      -- | The pattern is never a simple variable;
      -- That case is done by FunBind
      | PatBind {
            pat_lhs    :: LPat idL,
            pat_rhs    :: GRHSs idR (LHsExpr idR),
            pat_rhs_ty :: PostTcType,       -- ^ Type of the GRHSs
            bind_fvs   :: NameSet,          -- ^ See Note [Bind free vars]
            pat_ticks  :: (Maybe (Tickish Id), [Maybe (Tickish Id)])
                   -- ^ Tick to put on the rhs, if any, and ticks to put on
                   -- the bound variables.
        }

      -- | Dictionary binding and suchlike.
      -- All VarBinds are introduced by the type checker
      | VarBind {
            var_id     :: idL,
            var_rhs    :: LHsExpr idR,   -- ^ Located only for consistency
            var_inline :: Bool           -- ^ True <=> inline this binding regardless
                                         -- (used for implication constraints only)
        }

      | AbsBinds {                      -- Binds abstraction; TRANSLATION
            abs_tvs     :: [TyVar],
            abs_ev_vars :: [EvVar],  -- ^ Includes equality constraints

           -- | AbsBinds only gets used when idL = idR after renaming,
           -- but these need to be idL's for the collect... code in HsUtil
           -- to have the right type
            abs_exports :: [ABExport idL],

            abs_ev_binds :: TcEvBinds,     -- ^ Evidence bindings
            abs_binds    :: LHsBinds idL   -- ^ Typechecked user bindings
        }

      | PatSynBind {
            patsyn_id   :: Located idL,                   -- ^ Name of the pattern synonym
            bind_fvs    :: NameSet,                       -- ^ See Note [Bind free vars]
            patsyn_args :: HsPatSynDetails (Located idR), -- ^ Formal parameter names
            patsyn_def  :: LPat idR,                      -- ^ Right-hand side
            patsyn_dir  :: HsPatSynDir idR                -- ^ Directionality
        }

      deriving (Data, Typeable)
            -- Consider (AbsBinds tvs ds [(ftvs, poly_f, mono_f) binds]
            --
            -- Creates bindings for (polymorphic, overloaded) poly_f
            -- in terms of monomorphic, non-overloaded mono_f
            --
            -- Invariants:
            --      1. 'binds' binds mono_f
            --      2. ftvs is a subset of tvs
            --      3. ftvs includes all tyvars free in ds
            --
            -- See Note [AbsBinds]

    data ABExport id
      = ABE { abe_poly  :: id           -- ^ Any INLINE pragmas is attached to this Id
            , abe_mono  :: id
            , abe_wrap  :: HsWrapper    -- ^ See Note [AbsBinds wrappers]
                 -- Shape: (forall abs_tvs. abs_ev_vars => abe_mono) ~ abe_poly
            , abe_prags :: TcSpecPrags  -- ^ SPECIALISE pragmas
      } deriving (Data, Typeable)

    -- | Used for the NameSet in FunBind and PatBind prior to the renamer
    placeHolderNames :: NameSet
    placeHolderNames = panic "placeHolderNames"

\end{code} Note [AbsBinds] ~~~~~~~~~~~~~~~ The AbsBinds constructor is used in the output of the type checker, to record *typechecked* and *generalised* bindings. Consider a module M, with this top-level binding M.reverse [] = [] M.reverse (x:xs) = M.reverse xs ++ [x] In Hindley-Milner, a recursive binding is typechecked with the *recursive* uses being *monomorphic*. So after typechecking *and* desugaring we will get something like this M.reverse :: forall a. [a] -> [a] = /\a. letrec reverse :: [a] -> [a] = \xs -> case xs of [] -> [] (x:xs) -> reverse xs ++ [x] in reverse Notice that 'M.reverse' is polymorphic as expected, but there is a local definition for plain 'reverse' which is *monomorphic*. The type variable 'a' scopes over the entire letrec. That's after desugaring. What about after type checking but before desugaring? That's where AbsBinds comes in. It looks like this: AbsBinds { abs_tvs = [a] , abs_exports = [ABE { abe_poly = M.reverse :: forall a. [a] -> [a], , abe_mono = reverse :: a -> a}] , abs_binds = { reverse :: [a] -> [a] = \xs -> case xs of [] -> [] (x:xs) -> reverse xs ++ [x] } } Here, * abs_tvs says what type variables are abstracted over the binding group, just 'a' in this case. * abs_binds is the *monomorphic* bindings of the group * abs_exports describes how to get the polymorphic Id 'M.reverse' from the monomorphic one 'reverse' Notice that the *original* function (the polymorphic one you thought you were defining) appears in the abe_poly field of the abs_exports. The bindings in abs_binds are for fresh, local, Ids with a *monomorphic* Id. If there is a group of mutually recursive functions without type signatures, we get one AbsBinds with the monomorphic versions of the bindings in abs_binds, and one element of abe_exports for each variable bound in the mutually recursive group. This is true even for pattern bindings. Example: (f,g) = (\x -> x, f) After type checking we get AbsBinds { abs_tvs = [a] , abs_exports = [ ABE { abe_poly = M.f :: forall a. a -> a , abe_mono = f :: a -> a } , ABE { abe_poly = M.g :: forall a. a -> a , abe_mono = g :: a -> a }] , abs_binds = { (f,g) = (\x -> x, f) } Note [AbsBinds wrappers] ~~~~~~~~~~~~~~~~~~~~~~~~ Consider (f,g) = (\x.x, \y.y) This ultimately desugars to something like this: tup :: forall a b. (a->a, b->b) tup = /\a b. (\x:a.x, \y:b.y) f :: forall a. a -> a f = /\a. case tup a Any of (fm::a->a,gm:Any->Any) -> fm ...similarly for g... The abe_wrap field deals with impedence-matching between (/\a b. case tup a b of { (f,g) -> f }) and the thing we really want, which may have fewer type variables. The action happens in TcBinds.mkExport. Note [Bind free vars] ~~~~~~~~~~~~~~~~~~~~~ The bind_fvs field of FunBind and PatBind records the free variables of the definition. It is used for two purposes a) Dependency analysis prior to type checking (see TcBinds.tc_group) b) Deciding whether we can do generalisation of the binding (see TcBinds.decideGeneralisationPlan) Specifically, * bind_fvs includes all free vars that are defined in this module (including top-level things and lexically scoped type variables) * bind_fvs excludes imported vars; this is just to keep the set smaller * Before renaming, and after typechecking, the field is unused; it's just an error thunk \begin{code}

    instance (OutputableBndr idL, OutputableBndr idR) => Outputable (HsLocalBindsLR idL idR) where
      ppr (HsValBinds bs) = ppr bs
      ppr (HsIPBinds bs)  = ppr bs
      ppr EmptyLocalBinds = empty

    instance (OutputableBndr idL, OutputableBndr idR) => Outputable (HsValBindsLR idL idR) where
      ppr (ValBindsIn binds sigs)
       = pprDeclList (pprLHsBindsForUser binds sigs)

      ppr (ValBindsOut sccs sigs)
        = getPprStyle $ \ sty ->
          if debugStyle sty then    -- Print with sccs showing
            vcat (map ppr sigs) $$ vcat (map ppr_scc sccs)
         else
            pprDeclList (pprLHsBindsForUser (unionManyBags (map snd sccs)) sigs)
       where
         ppr_scc (rec_flag, binds) = pp_rec rec_flag <+> pprLHsBinds binds
         pp_rec Recursive    = ptext (sLit "rec")
         pp_rec NonRecursive = ptext (sLit "nonrec")

    pprLHsBinds :: (OutputableBndr idL, OutputableBndr idR) => LHsBindsLR idL idR -> SDoc
    pprLHsBinds binds
      | isEmptyLHsBinds binds = empty
      | otherwise = pprDeclList (map ppr (bagToList binds))

    pprLHsBindsForUser :: (OutputableBndr idL, OutputableBndr idR, OutputableBndr id2)
                       => LHsBindsLR idL idR -> [LSig id2] -> [SDoc]
    --  pprLHsBindsForUser is different to pprLHsBinds because
    --  a) No braces: 'let' and 'where' include a list of HsBindGroups
    --     and we don't want several groups of bindings each
    --     with braces around
    --  b) Sort by location before printing
    --  c) Include signatures
    pprLHsBindsForUser binds sigs
      = map snd (sort_by_loc decls)
      where

        decls :: [(SrcSpan, SDoc)]
        decls = [(loc, ppr sig)  | L loc sig <- sigs] ++
                [(loc, ppr bind) | L loc bind <- bagToList binds]

        sort_by_loc decls = sortBy (comparing fst) decls

    pprDeclList :: [SDoc] -> SDoc   -- Braces with a space
    -- Print a bunch of declarations
    -- One could choose  { d1; d2; ... }, using 'sep'
    -- or      d1
    --         d2
    --         ..
    --    using vcat
    -- At the moment we chose the latter
    -- Also we do the 'pprDeeperList' thing.
    pprDeclList ds = pprDeeperList vcat ds

    ------------
    emptyLocalBinds :: HsLocalBindsLR a b
    emptyLocalBinds = EmptyLocalBinds

    isEmptyLocalBinds :: HsLocalBindsLR a b -> Bool
    isEmptyLocalBinds (HsValBinds ds) = isEmptyValBinds ds
    isEmptyLocalBinds (HsIPBinds ds)  = isEmptyIPBinds ds
    isEmptyLocalBinds EmptyLocalBinds = True

    isEmptyValBinds :: HsValBindsLR a b -> Bool
    isEmptyValBinds (ValBindsIn ds sigs)  = isEmptyLHsBinds ds && null sigs
    isEmptyValBinds (ValBindsOut ds sigs) = null ds && null sigs

    emptyValBindsIn, emptyValBindsOut :: HsValBindsLR a b
    emptyValBindsIn  = ValBindsIn emptyBag []
    emptyValBindsOut = ValBindsOut []      []

    emptyLHsBinds :: LHsBindsLR idL idR
    emptyLHsBinds = emptyBag

    isEmptyLHsBinds :: LHsBindsLR idL idR -> Bool
    isEmptyLHsBinds = isEmptyBag

    ------------
    plusHsValBinds :: HsValBinds a -> HsValBinds a -> HsValBinds a
    plusHsValBinds (ValBindsIn ds1 sigs1) (ValBindsIn ds2 sigs2)
      = ValBindsIn (ds1 `unionBags` ds2) (sigs1 ++ sigs2)
    plusHsValBinds (ValBindsOut ds1 sigs1) (ValBindsOut ds2 sigs2)
      = ValBindsOut (ds1 ++ ds2) (sigs1 ++ sigs2)
    plusHsValBinds _ _
      = panic "HsBinds.plusHsValBinds"

    getTypeSigNames :: HsValBinds a -> NameSet
    -- Get the names that have a user type sig
    getTypeSigNames (ValBindsOut _ sigs)
      = mkNameSet [unLoc n | L _ (TypeSig names _) <- sigs, n <- names]
    getTypeSigNames _
      = panic "HsBinds.getTypeSigNames"

\end{code} What AbsBinds means ~~~~~~~~~~~~~~~~~~~ AbsBinds tvs [d1,d2] [(tvs1, f1p, f1m), (tvs2, f2p, f2m)] BIND means f1p = /\ tvs -> \ [d1,d2] -> letrec DBINDS and BIND in fm gp = ...same again, with gm instead of fm This is a pretty bad translation, because it duplicates all the bindings. So the desugarer tries to do a better job: fp = /\ [a,b] -> \ [d1,d2] -> case tp [a,b] [d1,d2] of (fm,gm) -> fm ..ditto for gp.. tp = /\ [a,b] -> \ [d1,d2] -> letrec DBINDS and BIND in (fm,gm) \begin{code}

    instance (OutputableBndr idL, OutputableBndr idR) => Outputable (HsBindLR idL idR) where
        ppr mbind = ppr_monobind mbind

    ppr_monobind :: (OutputableBndr idL, OutputableBndr idR) => HsBindLR idL idR -> SDoc

    ppr_monobind (PatBind { pat_lhs = pat, pat_rhs = grhss })
      = pprPatBind pat grhss
    ppr_monobind (VarBind { var_id = var, var_rhs = rhs })
      = sep [pprBndr CaseBind var, nest 2 $ equals <+> pprExpr (unLoc rhs)]
    ppr_monobind (FunBind { fun_id = fun, fun_infix = inf,
                            fun_co_fn = wrap,
                            fun_matches = matches,
                            fun_tick = tick })
      = pprTicks empty (case tick of
                            Nothing -> empty
                            Just t  -> text "-- tick id = " <> ppr t)
        $$  ifPprDebug (pprBndr LetBind (unLoc fun))
        $$  pprFunBind (unLoc fun) inf matches
        $$  ifPprDebug (ppr wrap)
    ppr_monobind (PatSynBind{ patsyn_id = L _ psyn, patsyn_args = details,
                              patsyn_def = pat, patsyn_dir = dir })
      = ppr_lhs <+> ppr_rhs
          where
            ppr_lhs = ptext (sLit "pattern") <+> ppr_details details
            ppr_simple syntax = syntax <+> ppr pat

            ppr_details (InfixPatSyn v1 v2) = hsep [ppr v1, pprInfixOcc psyn, ppr v2]
            ppr_details (PrefixPatSyn vs)   = hsep (pprPrefixOcc psyn : map ppr vs)

            ppr_rhs = case dir of
                Unidirectional         -> ppr_simple (ptext (sLit "<-"))
                ImplicitBidirectional  -> ppr_simple equals

    ppr_monobind (AbsBinds { abs_tvs = tyvars, abs_ev_vars = dictvars
                           , abs_exports = exports, abs_binds = val_binds
                           , abs_ev_binds = ev_binds })
      = hang (ptext (sLit "AbsBinds") <+> brackets (interpp'SP tyvars)
                                      <+> brackets (interpp'SP dictvars))
           2 $ braces $ vcat
        [ ptext (sLit "Exports:") <+> brackets (sep (punctuate comma (map ppr exports)))
        , ptext (sLit "Exported types:") <+> vcat [pprBndr LetBind (abe_poly ex) | ex <- exports]
        , ptext (sLit "Binds:") <+> pprLHsBinds val_binds
        , ifPprDebug (ptext (sLit "Evidence:") <+> ppr ev_binds) ]

    instance (OutputableBndr id) => Outputable (ABExport id) where
      ppr (ABE { abe_wrap = wrap, abe_poly = gbl, abe_mono = lcl, abe_prags = prags })
        = vcat [ ppr gbl <+> ptext (sLit "<=") <+> ppr lcl
               , nest 2 (pprTcSpecPrags prags)
               , nest 2 (ppr wrap)]

\end{code} \begin{code}

    pprTicks :: SDoc -> SDoc -> SDoc
    -- Print stuff about ticks only when -dppr-debug is on, to avoid
    -- them appearing in error messages (from the desugarer); see Trac # 3263
    -- Also print ticks in dumpStyle, so that -ddump-hpc actually does
    -- something useful.
    pprTicks pp_no_debug pp_when_debug
      = getPprStyle (\ sty -> if debugStyle sty || dumpStyle sty
                                 then pp_when_debug
                                 else pp_no_debug)

\end{code} %************************************************************************ %* * Implicit parameter bindings %* * %************************************************************************ \begin{code}

    data HsIPBinds id
      = IPBinds
            [LIPBind id]
            TcEvBinds       -- Only in typechecker output; binds
                            -- uses of the implicit parameters
      deriving (Data, Typeable)

    isEmptyIPBinds :: HsIPBinds id -> Bool
    isEmptyIPBinds (IPBinds is ds) = null is && isEmptyTcEvBinds ds

    type LIPBind id = Located (IPBind id)

    -- | Implicit parameter bindings.
    {- These bindings start off as (Left "x") in the parser and stay
    that way until after type-checking when they are replaced with
    (Right d), where "d" is the name of the dictionary holding the
    evidene for the implicit parameter. -}
    data IPBind id
      = IPBind (Either HsIPName id) (LHsExpr id)
      deriving (Data, Typeable)

    instance (OutputableBndr id) => Outputable (HsIPBinds id) where
      ppr (IPBinds bs ds) = pprDeeperList vcat (map ppr bs)
                            $$ ifPprDebug (ppr ds)

    instance (OutputableBndr id) => Outputable (IPBind id) where
      ppr (IPBind lr rhs) = name <+> equals <+> pprExpr (unLoc rhs)
        where name = case lr of
                       Left ip  -> pprBndr LetBind ip
                       Right id -> pprBndr LetBind id

\end{code} %************************************************************************ %* * \subsection{@Sig@: type signatures and value-modifying user pragmas} %* * %************************************************************************ It is convenient to lump ``value-modifying'' user-pragmas (e.g., ``specialise this function to these four types...'') in with type signatures. Then all the machinery to move them into place, etc., serves for both. \begin{code}

    type LSig name = Located (Sig name)

    -- | Signatures and pragmas
    data Sig name
      =   -- | An ordinary type signature
          -- @f :: Num a => a -> a@
        TypeSig [Located name] (LHsType name)

          -- | A pattern synonym type signature
          -- @pattern (Eq b) => P a b :: (Num a) => T a
      | PatSynSig (Located name)
                  (HsPatSynDetails (LHsType name))
                  (LHsType name)    -- Type
                  (LHsContext name) -- Provided context
                  (LHsContext name) -- Required contex

            -- | A type signature for a default method inside a class
            --
            -- > default eq :: (Representable0 a, GEq (Rep0 a)) => a -> a -> Bool
            --
      | GenericSig [Located name] (LHsType name)

            -- | A type signature in generated code, notably the code
            -- generated for record selectors.  We simply record
            -- the desired Id itself, replete with its name, type
            -- and IdDetails.  Otherwise it's just like a type
            -- signature: there should be an accompanying binding
      | IdSig Id

            -- | An ordinary fixity declaration
            --
            -- >     infixl *** 8
            --
      | FixSig (FixitySig name)

            -- | An inline pragma
            --
            -- > {#- INLINE f #-}
            --
      | InlineSig   (Located name)  -- Function name
                    InlinePragma    -- Never defaultInlinePragma

            -- | A specialisation pragma
            --
            -- > {-# SPECIALISE f :: Int -> Int #-}
            --
      | SpecSig     (Located name)  -- Specialise a function or datatype  ...
                    (LHsType name)  -- ... to these types
                    InlinePragma    -- The pragma on SPECIALISE_INLINE form.
                                    -- If it's just defaultInlinePragma, then we said
                                    --    SPECIALISE, not SPECIALISE_INLINE

            -- | A specialisation pragma for instance declarations only
            --
            -- > {-# SPECIALISE instance Eq [Int] #-}
            --
            -- (Class tys); should be a specialisation of the
            -- current instance declaration
      | SpecInstSig (LHsType name)

            -- | A minimal complete definition pragma
            --
            -- > {-# MINIMAL a | (b, c | (d | e)) #-}
      | MinimalSig (BooleanFormula (Located name))

      deriving (Data, Typeable)

    type LFixitySig name = Located (FixitySig name)
    data FixitySig name = FixitySig (Located name) Fixity
      deriving (Data, Typeable)

    -- | TsSpecPrags conveys pragmas from the type checker to the desugarer
    data TcSpecPrags
      = IsDefaultMethod     -- ^ Super-specialised: a default method should
                            -- be macro-expanded at every call site
      | SpecPrags [LTcSpecPrag]
      deriving (Data, Typeable)

    type LTcSpecPrag = Located TcSpecPrag

    data TcSpecPrag
      = SpecPrag
            Id
            HsWrapper
            InlinePragma
      -- ^ The Id to be specialised, an wrapper that specialises the
      -- polymorphic function, and inlining spec for the specialised function
      deriving (Data, Typeable)

    noSpecPrags :: TcSpecPrags
    noSpecPrags = SpecPrags []

    hasSpecPrags :: TcSpecPrags -> Bool
    hasSpecPrags (SpecPrags ps) = not (null ps)
    hasSpecPrags IsDefaultMethod = False

    isDefaultMethod :: TcSpecPrags -> Bool
    isDefaultMethod IsDefaultMethod = True
    isDefaultMethod (SpecPrags {})  = False

    isFixityLSig :: LSig name -> Bool
    isFixityLSig (L _ (FixSig {})) = True
    isFixityLSig _                 = False

    isVanillaLSig :: LSig name -> Bool       -- User type signatures
    -- A badly-named function, but it's part of the GHCi (used
    -- by Haddock) so I don't want to change it gratuitously.
    isVanillaLSig (L _(TypeSig {})) = True
    isVanillaLSig _                 = False

    isTypeLSig :: LSig name -> Bool  -- Type signatures
    isTypeLSig (L _(TypeSig {}))    = True
    isTypeLSig (L _(GenericSig {})) = True
    isTypeLSig (L _(IdSig {}))      = True
    isTypeLSig _                    = False

    isSpecLSig :: LSig name -> Bool
    isSpecLSig (L _(SpecSig {})) = True
    isSpecLSig _                 = False

    isSpecInstLSig :: LSig name -> Bool
    isSpecInstLSig (L _ (SpecInstSig {})) = True
    isSpecInstLSig _                      = False

    isPragLSig :: LSig name -> Bool
    -- Identifies pragmas
    isPragLSig (L _ (SpecSig {}))   = True
    isPragLSig (L _ (InlineSig {})) = True
    isPragLSig _                    = False

    isInlineLSig :: LSig name -> Bool
    -- Identifies inline pragmas
    isInlineLSig (L _ (InlineSig {})) = True
    isInlineLSig _                    = False

    isMinimalLSig :: LSig name -> Bool
    isMinimalLSig (L _ (MinimalSig {})) = True
    isMinimalLSig _                    = False

    hsSigDoc :: Sig name -> SDoc
    hsSigDoc (TypeSig {})           = ptext (sLit "type signature")
    hsSigDoc (PatSynSig {})         = ptext (sLit "pattern synonym signature")
    hsSigDoc (GenericSig {})        = ptext (sLit "default type signature")
    hsSigDoc (IdSig {})             = ptext (sLit "id signature")
    hsSigDoc (SpecSig {})           = ptext (sLit "SPECIALISE pragma")
    hsSigDoc (InlineSig _ prag)     = ppr (inlinePragmaSpec prag) <+> ptext (sLit "pragma")
    hsSigDoc (SpecInstSig {})       = ptext (sLit "SPECIALISE instance pragma")
    hsSigDoc (FixSig {})            = ptext (sLit "fixity declaration")
    hsSigDoc (MinimalSig {})        = ptext (sLit "MINIMAL pragma")

\end{code} Check if signatures overlap; this is used when checking for duplicate signatures. Since some of the signatures contain a list of names, testing for equality is not enough -- we have to check if they overlap. \begin{code}

    instance (OutputableBndr name) => Outputable (Sig name) where
        ppr sig = ppr_sig sig

    ppr_sig :: OutputableBndr name => Sig name -> SDoc
    ppr_sig (TypeSig vars ty)         = pprVarSig (map unLoc vars) (ppr ty)
    ppr_sig (GenericSig vars ty)      = ptext (sLit "default") <+> pprVarSig (map unLoc vars) (ppr ty)
    ppr_sig (IdSig id)                = pprVarSig [id] (ppr (varType id))
    ppr_sig (FixSig fix_sig)          = ppr fix_sig
    ppr_sig (SpecSig var ty inl)      = pragBrackets (pprSpec (unLoc var) (ppr ty) inl)
    ppr_sig (InlineSig var inl)       = pragBrackets (ppr inl <+> pprPrefixOcc (unLoc var))
    ppr_sig (SpecInstSig ty)          = pragBrackets (ptext (sLit "SPECIALIZE instance") <+> ppr ty)
    ppr_sig (MinimalSig bf)           = pragBrackets (pprMinimalSig bf)
    ppr_sig (PatSynSig name arg_tys ty prov req)
      = pprPatSynSig (unLoc name) False args (ppr ty) (pprCtx prov) (pprCtx req)
      where
        args = fmap ppr arg_tys

        pprCtx lctx = case unLoc lctx of
            [] -> Nothing
            ctx -> Just (pprHsContextNoArrow ctx)

    pprPatSynSig :: (OutputableBndr a)
                 => a -> Bool -> HsPatSynDetails SDoc -> SDoc -> Maybe SDoc -> Maybe SDoc -> SDoc
    pprPatSynSig ident is_bidir args rhs_ty prov_theta req_theta
      = sep [ ptext (sLit "pattern")
            , thetaOpt prov_theta, name_and_args
            , colon
            , thetaOpt req_theta, rhs_ty
            ]
      where
        name_and_args = case args of
            PrefixPatSyn arg_tys ->
                pprPrefixOcc ident <+> sep arg_tys
            InfixPatSyn left_ty right_ty ->
                left_ty <+> pprInfixOcc ident <+> right_ty

        -- TODO: support explicit foralls
        thetaOpt = maybe empty (<+> darrow)

        colon = if is_bidir then dcolon else dcolon -- TODO

    instance OutputableBndr name => Outputable (FixitySig name) where
      ppr (FixitySig name fixity) = sep [ppr fixity, pprInfixOcc (unLoc name)]

    pragBrackets :: SDoc -> SDoc
    pragBrackets doc = ptext (sLit "{-#") <+> doc <+> ptext (sLit "#-}")

    pprVarSig :: (OutputableBndr id) => [id] -> SDoc -> SDoc
    pprVarSig vars pp_ty = sep [pprvars <+> dcolon, nest 2 pp_ty]
      where
        pprvars = hsep $ punctuate comma (map pprPrefixOcc vars)

    pprSpec :: (OutputableBndr id) => id -> SDoc -> InlinePragma -> SDoc
    pprSpec var pp_ty inl = ptext (sLit "SPECIALIZE") <+> pp_inl <+> pprVarSig [var] pp_ty
      where
        pp_inl | isDefaultInlinePragma inl = empty
               | otherwise = ppr inl

    pprTcSpecPrags :: TcSpecPrags -> SDoc
    pprTcSpecPrags IsDefaultMethod = ptext (sLit "<default method>")
    pprTcSpecPrags (SpecPrags ps)  = vcat (map (ppr . unLoc) ps)

    instance Outputable TcSpecPrag where
      ppr (SpecPrag var _ inl) = pprSpec var (ptext (sLit "<type>")) inl

    pprMinimalSig :: OutputableBndr name => BooleanFormula (Located name) -> SDoc
    pprMinimalSig bf = ptext (sLit "MINIMAL") <+> ppr (fmap unLoc bf)

\end{code} %************************************************************************ %* * \subsection[PatSynBind]{A pattern synonym definition} %* * %************************************************************************ \begin{code}

    data HsPatSynDetails a
      = InfixPatSyn a a
      | PrefixPatSyn [a]
      deriving (Data, Typeable)

    instance Functor HsPatSynDetails where
        fmap f (InfixPatSyn left right) = InfixPatSyn (f left) (f right)
        fmap f (PrefixPatSyn args) = PrefixPatSyn (fmap f args)

    instance Foldable HsPatSynDetails where
        foldMap f (InfixPatSyn left right) = f left `mappend` f right
        foldMap f (PrefixPatSyn args) = foldMap f args

    instance Traversable HsPatSynDetails where
        traverse f (InfixPatSyn left right) = InfixPatSyn <$> f left <*> f right
        traverse f (PrefixPatSyn args) = PrefixPatSyn <$> traverse f args

    data HsPatSynDirLR idL idR
      = Unidirectional
      | ImplicitBidirectional
      deriving (Data, Typeable)

    type HsPatSynDir id = HsPatSynDirLR id id

\end{code}