path: root/compiler/GHC/Hs/Binds.hs

{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE UndecidableInstances #-} -- Wrinkle in Note [Trees That Grow]
                                      -- in module Language.Haskell.Syntax.Extension
{-# LANGUAGE ViewPatterns #-}

{-# OPTIONS_GHC -Wno-orphans #-} -- Outputable

{-
(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@.
-}

module GHC.Hs.Binds
  ( module Language.Haskell.Syntax.Binds
  , module GHC.Hs.Binds
  ) where

import GHC.Prelude

import Language.Haskell.Syntax.Binds

import {-# SOURCE #-} GHC.Hs.Expr ( pprExpr, pprFunBind, pprPatBind )

import Language.Haskell.Syntax.Extension
import GHC.Hs.Extension
import GHC.Hs.Type
import GHC.Tc.Types.Evidence
import GHC.Core.Type
import GHC.Types.Name.Set
import GHC.Types.Basic
import GHC.Types.SourceText
import GHC.Types.SrcLoc as SrcLoc
import GHC.Data.Bag
import GHC.Data.FastString
import GHC.Data.BooleanFormula (LBooleanFormula)

import GHC.Utils.Outputable
import GHC.Utils.Panic

import Data.List hiding ( foldr )
import Data.Function

{-
************************************************************************
*                                                                      *
\subsection{Bindings: @BindGroup@}
*                                                                      *
************************************************************************

Global bindings (where clauses)
-}

-- the ...LR datatypes are parametrized by two id types,
-- one for the left and one for the right.

type instance XHsValBinds      (GhcPass pL) (GhcPass pR) = NoExtField
type instance XHsIPBinds       (GhcPass pL) (GhcPass pR) = NoExtField
type instance XEmptyLocalBinds (GhcPass pL) (GhcPass pR) = NoExtField
type instance XXHsLocalBindsLR (GhcPass pL) (GhcPass pR) = NoExtCon

-- ---------------------------------------------------------------------
-- Deal with ValBindsOut

-- TODO: make this the only type for ValBinds
data NHsValBindsLR idL
  = NValBinds
      [(RecFlag, LHsBinds idL)]
      [LSig GhcRn]

type instance XValBinds    (GhcPass pL) (GhcPass pR) = NoExtField
type instance XXValBindsLR (GhcPass pL) (GhcPass pR)
            = NHsValBindsLR (GhcPass pL)

-- ---------------------------------------------------------------------

type instance XFunBind    (GhcPass pL) GhcPs = NoExtField
type instance XFunBind    (GhcPass pL) GhcRn = NameSet    -- Free variables
type instance XFunBind    (GhcPass pL) GhcTc = HsWrapper  -- See comments on FunBind.fun_ext

type instance XPatBind    GhcPs (GhcPass pR) = NoExtField
type instance XPatBind    GhcRn (GhcPass pR) = NameSet -- Free variables
type instance XPatBind    GhcTc (GhcPass pR) = Type    -- Type of the GRHSs

type instance XVarBind    (GhcPass pL) (GhcPass pR) = NoExtField
type instance XAbsBinds   (GhcPass pL) (GhcPass pR) = NoExtField
type instance XPatSynBind (GhcPass pL) (GhcPass pR) = NoExtField
type instance XXHsBindsLR (GhcPass pL) (GhcPass pR) = NoExtCon

type instance XABE       (GhcPass p) = NoExtField
type instance XXABExport (GhcPass p) = NoExtCon

type instance XPSB         (GhcPass idL) GhcPs = NoExtField
type instance XPSB         (GhcPass idL) GhcRn = NameSet
type instance XPSB         (GhcPass idL) GhcTc = NameSet

type instance XXPatSynBind (GhcPass idL) (GhcPass idR) = NoExtCon

{-
Note [AbsBinds]
~~~~~~~~~~~~~~~
The AbsBinds constructor is used in the output of the type checker, to
record *typechecked* and *generalised* bindings.  Specifically

         AbsBinds { abs_tvs      = tvs
                  , abs_ev_vars  = [d1,d2]
                  , abs_exports  = [ABE { abe_poly = fp, abe_mono = fm
                                        , abe_wrap = fwrap }
                                    ABE { slly for g } ]
                  , abs_ev_binds = DBINDS
                  , abs_binds    = BIND[fm,gm] }

where 'BIND' binds the monomorphic Ids 'fm' and 'gm', means

        fp = fwrap [/\ tvs. \d1 d2. letrec { DBINDS        ]
                   [                       ; BIND[fm,gm] } ]
                   [                 in fm                 ]

        gp = ...same again, with gm instead of fm

The 'fwrap' is an impedance-matcher that typically does nothing; see
Note [ABExport wrapper].

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; BIND }
                                      in (fm,gm)

In general:

  * abs_tvs are the type variables over which the binding group is
    generalised
  * abs_ev_var are the evidence variables (usually dictionaries)
    over which the binding group is generalised
  * abs_binds are the monomorphic bindings
  * abs_ex_binds are the evidence bindings that wrap the abs_binds
  * abs_exports connects the monomorphic Ids bound by abs_binds
    with the polymorphic Ids bound by the AbsBinds itself.

For example, consider a module M, with this top-level binding, where
there is no type signature for M.reverse,
    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_ev_vars = []
            , abs_exports = [ABE { abe_poly = M.reverse :: forall a. [a] -> [a],
                                 , abe_mono = reverse :: [a] -> [a]}]
            , abs_ev_binds = {}
            , 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 (see Note [Polymorphic
recursion]) 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 [Polymorphic recursion]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
   Rec { f x = ...(g ef)...

       ; g :: forall a. [a] -> [a]
       ; g y = ...(f eg)...  }

These bindings /are/ mutually recursive (f calls g, and g calls f).
But we can use the type signature for g to break the recursion,
like this:

  1. Add g :: forall a. [a] -> [a] to the type environment

  2. Typecheck the definition of f, all by itself,
     including generalising it to find its most general
     type, say f :: forall b. b -> b -> [b]

  3. Extend the type environment with that type for f

  4. Typecheck the definition of g, all by itself,
     checking that it has the type claimed by its signature

Steps 2 and 4 each generate a separate AbsBinds, so we end
up with
   Rec { AbsBinds { ...for f ... }
       ; AbsBinds { ...for g ... } }

This approach allows both f and to call each other
polymorphically, even though only g has a signature.

We get an AbsBinds that encompasses multiple source-program
bindings only when
 * Each binding in the group has at least one binder that
   lacks a user type signature
 * The group forms a strongly connected component


Note [The abs_sig field of AbsBinds]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The abs_sig field supports a couple of special cases for bindings.
Consider

  x :: Num a => (# a, a #)
  x = (# 3, 4 #)

The general desugaring for AbsBinds would give

  x = /\a. \ ($dNum :: Num a) ->
      letrec xm = (# fromInteger $dNum 3, fromInteger $dNum 4 #) in
      xm

But that has an illegal let-binding for an unboxed tuple.  In this
case we'd prefer to generate the (more direct)

  x = /\ a. \ ($dNum :: Num a) ->
     (# fromInteger $dNum 3, fromInteger $dNum 4 #)

A similar thing happens with representation-polymorphic defns
(#11405):

  undef :: forall (r :: RuntimeRep) (a :: TYPE r). HasCallStack => a
  undef = error "undef"

Again, the vanilla desugaring gives a local let-binding for a
representation-polymorphic (undefm :: a), which is illegal.  But
again we can desugar without a let:

  undef = /\ a. \ (d:HasCallStack) -> error a d "undef"

The abs_sig field supports this direct desugaring, with no local
let-binding.  When abs_sig = True

 * the abs_binds is single FunBind

 * the abs_exports is a singleton

 * we have a complete type sig for binder
   and hence the abs_binds is non-recursive
   (it binds the mono_id but refers to the poly_id

These properties are exploited in GHC.HsToCore.Binds.dsAbsBinds to
generate code without a let-binding.

Note [ABExport wrapper]
~~~~~~~~~~~~~~~~~~~~~~~
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 impedance-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 GHC.Tc.Gen.Bind.mkExport.

Note [Bind free vars]
~~~~~~~~~~~~~~~~~~~~~
The bind_fvs field of FunBind and PatBind records the free variables
of the definition.  It is used for the following purposes

a) Dependency analysis prior to type checking
    (see GHC.Tc.Gen.Bind.tc_group)

b) Deciding whether we can do generalisation of the binding
    (see GHC.Tc.Gen.Bind.decideGeneralisationPlan)

c) Deciding whether the binding can be used in static forms
    (see GHC.Tc.Gen.Expr.checkClosedInStaticForm for the HsStatic case and
     GHC.Tc.Gen.Bind.isClosedBndrGroup).

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
-}

instance (OutputableBndrId pl, OutputableBndrId pr)
        => Outputable (HsLocalBindsLR (GhcPass pl) (GhcPass pr)) where
  ppr (HsValBinds _ bs)   = ppr bs
  ppr (HsIPBinds _ bs)    = ppr bs
  ppr (EmptyLocalBinds _) = empty

instance (OutputableBndrId pl, OutputableBndrId pr)
        => Outputable (HsValBindsLR (GhcPass pl) (GhcPass pr)) where
  ppr (ValBinds _ binds sigs)
   = pprDeclList (pprLHsBindsForUser binds sigs)

  ppr (XValBindsLR (NValBinds sccs sigs))
    = getPprDebug $ \case
        -- Print with sccs showing
        True  -> vcat (map ppr sigs) $$ vcat (map ppr_scc sccs)
        False -> pprDeclList (pprLHsBindsForUser (unionManyBags (map snd sccs)) sigs)
   where
     ppr_scc (rec_flag, binds) = pp_rec rec_flag <+> pprLHsBinds binds
     pp_rec Recursive    = text "rec"
     pp_rec NonRecursive = text "nonrec"

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

pprLHsBindsForUser :: (OutputableBndrId idL,
                       OutputableBndrId idR,
                       OutputableBndrId id2)
     => LHsBindsLR (GhcPass idL) (GhcPass idR) -> [LSig (GhcPass 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 (SrcLoc.leftmost_smallest `on` 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 (GhcPass a) (GhcPass b)
emptyLocalBinds = EmptyLocalBinds noExtField

eqEmptyLocalBinds :: HsLocalBindsLR a b -> Bool
eqEmptyLocalBinds (EmptyLocalBinds _) = True
eqEmptyLocalBinds _                   = False

isEmptyValBinds :: HsValBindsLR (GhcPass a) (GhcPass b) -> Bool
isEmptyValBinds (ValBinds _ ds sigs)  = isEmptyLHsBinds ds && null sigs
isEmptyValBinds (XValBindsLR (NValBinds ds sigs)) = null ds && null sigs

emptyValBindsIn, emptyValBindsOut :: HsValBindsLR (GhcPass a) (GhcPass b)
emptyValBindsIn  = ValBinds noExtField emptyBag []
emptyValBindsOut = XValBindsLR (NValBinds [] [])

emptyLHsBinds :: LHsBindsLR (GhcPass idL) idR
emptyLHsBinds = emptyBag

isEmptyLHsBinds :: LHsBindsLR (GhcPass idL) idR -> Bool
isEmptyLHsBinds = isEmptyBag

------------
plusHsValBinds :: HsValBinds (GhcPass a) -> HsValBinds (GhcPass a)
               -> HsValBinds(GhcPass a)
plusHsValBinds (ValBinds _ ds1 sigs1) (ValBinds _ ds2 sigs2)
  = ValBinds noExtField (ds1 `unionBags` ds2) (sigs1 ++ sigs2)
plusHsValBinds (XValBindsLR (NValBinds ds1 sigs1))
               (XValBindsLR (NValBinds ds2 sigs2))
  = XValBindsLR (NValBinds (ds1 ++ ds2) (sigs1 ++ sigs2))
plusHsValBinds _ _
  = panic "HsBinds.plusHsValBinds"

instance (OutputableBndrId pl, OutputableBndrId pr)
         => Outputable (HsBindLR (GhcPass pl) (GhcPass pr)) where
    ppr mbind = ppr_monobind mbind

ppr_monobind :: forall idL idR.
                (OutputableBndrId idL, OutputableBndrId idR)
             => HsBindLR (GhcPass idL) (GhcPass 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 CasePatBind var, nest 2 $ equals <+> pprExpr (unLoc rhs)]
ppr_monobind (FunBind { fun_id = fun,
                        fun_matches = matches,
                        fun_tick = ticks,
                        fun_ext = wrap })
  = pprTicks empty (if null ticks then empty
                    else text "-- ticks = " <> ppr ticks)
    $$  whenPprDebug (pprBndr LetBind (unLoc fun))
    $$  pprFunBind  matches
    $$  whenPprDebug (pprIfTc @idR $ ppr wrap)

ppr_monobind (PatSynBind _ psb) = ppr psb
ppr_monobind (AbsBinds { abs_tvs = tyvars, abs_ev_vars = dictvars
                       , abs_exports = exports, abs_binds = val_binds
                       , abs_ev_binds = ev_binds })
  = sdocOption sdocPrintTypecheckerElaboration $ \case
      False -> pprLHsBinds val_binds
      True  -> -- Show extra information (bug number: #10662)
               hang (text "AbsBinds"
                     <+> sep [ brackets (interpp'SP tyvars)
                             , brackets (interpp'SP dictvars) ])
                  2 $ braces $ vcat
               [ text "Exports:" <+>
                   brackets (sep (punctuate comma (map ppr exports)))
               , text "Exported types:" <+>
                   vcat [pprBndr LetBind (abe_poly ex) | ex <- exports]
               , text "Binds:" <+> pprLHsBinds val_binds
               , pprIfTc @idR (text "Evidence:" <+> ppr ev_binds)
               ]

instance OutputableBndrId p => Outputable (ABExport (GhcPass p)) where
  ppr (ABE { abe_wrap = wrap, abe_poly = gbl, abe_mono = lcl, abe_prags = prags })
    = vcat [ sep [ ppr gbl, nest 2 (text "<=" <+> ppr lcl) ]
           , nest 2 (pprTcSpecPrags prags)
           , pprIfTc @p $ nest 2 (text "wrap:" <+> ppr wrap) ]

instance (OutputableBndrId l, OutputableBndrId r,
         Outputable (XXPatSynBind (GhcPass l) (GhcPass r)))
          => Outputable (PatSynBind (GhcPass l) (GhcPass r)) where
  ppr (PSB{ psb_id = (L _ psyn), psb_args = details, psb_def = pat,
            psb_dir = dir })
      = ppr_lhs <+> ppr_rhs
    where
      ppr_lhs = text "pattern" <+> ppr_details
      ppr_simple syntax = syntax <+> ppr pat

      ppr_details = case details of
          InfixCon v1 v2 -> hsep [ppr v1, pprInfixOcc psyn, ppr v2]
          PrefixCon _ vs -> hsep (pprPrefixOcc psyn : map ppr vs)
          RecCon vs      -> pprPrefixOcc psyn
                            <> braces (sep (punctuate comma (map ppr vs)))

      ppr_rhs = case dir of
          Unidirectional           -> ppr_simple (text "<-")
          ImplicitBidirectional    -> ppr_simple equals
          ExplicitBidirectional mg -> ppr_simple (text "<-") <+> ptext (sLit "where") $$
                                      (nest 2 $ pprFunBind mg)

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 # 3263
-- Also print ticks in dumpStyle, so that -ddump-hpc actually does
-- something useful.
pprTicks pp_no_debug pp_when_debug
  = getPprStyle $ \sty ->
    getPprDebug $ \debug ->
      if debug || dumpStyle sty
         then pp_when_debug
         else pp_no_debug

{-
************************************************************************
*                                                                      *
                Implicit parameter bindings
*                                                                      *
************************************************************************
-}

type instance XIPBinds       GhcPs = NoExtField
type instance XIPBinds       GhcRn = NoExtField
type instance XIPBinds       GhcTc = TcEvBinds -- binds uses of the
                                               -- implicit parameters


type instance XXHsIPBinds    (GhcPass p) = NoExtCon

isEmptyIPBindsPR :: HsIPBinds (GhcPass p) -> Bool
isEmptyIPBindsPR (IPBinds _ is) = null is

isEmptyIPBindsTc :: HsIPBinds GhcTc -> Bool
isEmptyIPBindsTc (IPBinds ds is) = null is && isEmptyTcEvBinds ds

type instance XCIPBind    (GhcPass p) = NoExtField
type instance XXIPBind    (GhcPass p) = NoExtCon

instance OutputableBndrId p
       => Outputable (HsIPBinds (GhcPass p)) where
  ppr (IPBinds ds bs) = pprDeeperList vcat (map ppr bs)
                        $$ whenPprDebug (pprIfTc @p $ ppr ds)

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

{-
************************************************************************
*                                                                      *
\subsection{@Sig@: type signatures and value-modifying user pragmas}
*                                                                      *
************************************************************************
-}

type instance XTypeSig          (GhcPass p) = NoExtField
type instance XPatSynSig        (GhcPass p) = NoExtField
type instance XClassOpSig       (GhcPass p) = NoExtField
type instance XIdSig            (GhcPass p) = NoExtField
type instance XFixSig           (GhcPass p) = NoExtField
type instance XInlineSig        (GhcPass p) = NoExtField
type instance XSpecSig          (GhcPass p) = NoExtField
type instance XSpecInstSig      (GhcPass p) = NoExtField
type instance XMinimalSig       (GhcPass p) = NoExtField
type instance XSCCFunSig        (GhcPass p) = NoExtField
type instance XCompleteMatchSig (GhcPass p) = NoExtField
type instance XXSig             (GhcPass p) = NoExtCon

type instance XFixitySig  (GhcPass p) = NoExtField
type instance XXFixitySig (GhcPass p) = NoExtCon

instance OutputableBndrId p => Outputable (Sig (GhcPass p)) where
    ppr sig = ppr_sig sig

ppr_sig :: (OutputableBndrId p) => Sig (GhcPass p) -> SDoc
ppr_sig (TypeSig _ vars ty)  = pprVarSig (map unLoc vars) (ppr ty)
ppr_sig (ClassOpSig _ is_deflt vars ty)
  | is_deflt                 = text "default" <+> pprVarSig (map unLoc vars) (ppr ty)
  | otherwise                = 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@(InlinePragma { inl_inline = spec }))
  = pragSrcBrackets (inl_src inl) pragmaSrc (pprSpec (unLoc var)
                                             (interpp'SP ty) inl)
    where
      pragmaSrc = case spec of
        NoUserInlinePrag -> "{-# SPECIALISE"
        _                -> "{-# SPECIALISE_INLINE"
ppr_sig (InlineSig _ var inl)
  = pragSrcBrackets (inl_src inl) "{-# INLINE"  (pprInline inl
                                   <+> pprPrefixOcc (unLoc var))
ppr_sig (SpecInstSig _ src ty)
  = pragSrcBrackets src "{-# pragma" (text "instance" <+> ppr ty)
ppr_sig (MinimalSig _ src bf)
  = pragSrcBrackets src "{-# MINIMAL" (pprMinimalSig bf)
ppr_sig (PatSynSig _ names sig_ty)
  = text "pattern" <+> pprVarSig (map unLoc names) (ppr sig_ty)
ppr_sig (SCCFunSig _ src fn mlabel)
  = pragSrcBrackets src "{-# SCC" (ppr fn <+> maybe empty ppr mlabel )
ppr_sig (CompleteMatchSig _ src cs mty)
  = pragSrcBrackets src "{-# COMPLETE"
      ((hsep (punctuate comma (map ppr (unLoc cs))))
        <+> opt_sig)
  where
    opt_sig = maybe empty ((\t -> dcolon <+> ppr t) . unLoc) mty

instance OutputableBndrId p
       => Outputable (FixitySig (GhcPass p)) where
  ppr (FixitySig _ names fixity) = sep [ppr fixity, pprops]
    where
      pprops = hsep $ punctuate comma (map (pprInfixOcc . unLoc) names)

pragBrackets :: SDoc -> SDoc
pragBrackets doc = text "{-#" <+> doc <+> text "#-}"

-- | Using SourceText in case the pragma was spelled differently or used mixed
-- case
pragSrcBrackets :: SourceText -> String -> SDoc -> SDoc
pragSrcBrackets (SourceText src) _   doc = text src <+> doc <+> text "#-}"
pragSrcBrackets NoSourceText     alt doc = text alt <+> doc <+> text "#-}"

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 = pp_inl <+> pprVarSig [var] pp_ty
  where
    pp_inl | isDefaultInlinePragma inl = empty
           | otherwise = pprInline inl

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

instance Outputable TcSpecPrag where
  ppr (SpecPrag var _ inl)
    = text "SPECIALIZE" <+> pprSpec var (text "<type>") inl

pprMinimalSig :: (OutputableBndr name)
              => LBooleanFormula (Located name) -> SDoc
pprMinimalSig (L _ bf) = ppr (fmap unLoc bf)