{-
(c) The University of Glasgow 2006
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998
-}

{-# LANGUAGE CPP, DeriveDataTypeable, ScopedTypeVariables #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE UndecidableInstances #-} -- Note [Pass sensitive types]
                                      -- in module PlaceHolder
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE DeriveFunctor #-}

-- | Abstract Haskell syntax for expressions.
module Language.Haskell.Syntax.HsExpr
             (SrcLoc,
              LHsExpr,
              LGRHS,
              LMatch,
              LStmt,
              LHsCmd,
              LHsTupArg,
              LHsCmdTop,
              LStmtLR,
              CmdLStmt,
              ParStmtBlock(..),
              HsArrAppType(..),
              HsCmdTop(..),
              HsExpr(..),
              GRHS(..),
              GRHSs(..),
              HsTupArg(..),
              HsSplice(..),
              MatchGroup(..),
              Match(..),
              HsCmd(..),
              HsStmtContext (..),
              ExprLStmt,
              StmtLR(..),
              TransForm(..),
              ArithSeqInfo(..),
              HsMatchContext (..),
              FunctionFixity(..),
              HsBracket(..),
              CmdStmt(..),
              Stmt(..),
              HsRecordBinds(..),
              ExprStmt(..)) where

-- friends:
import Language.Haskell.Syntax.HsDecls
import Language.Haskell.Syntax.HsPat
import Language.Haskell.Syntax.HsLit
import Language.Haskell.Syntax.HsTypes
import Language.Haskell.Syntax.HsBinds

import Language.Haskell.Syntax.BasicTypes
import Language.Haskell.Utility.FastString
import Language.Haskell.Syntax.SrcLoc

-- libraries:
import Data.Data hiding (Fixity(..))

{-
************************************************************************
*                                                                      *
\subsection{Expressions proper}
*                                                                      *
************************************************************************
-}

-- * Expressions proper

type LHsExpr id = Located (HsExpr id)

-- | A Haskell expression.
data HsExpr id
  = HsVar     (Located id)   -- ^ Variable

                             -- See Note [Located RdrNames]

  | HsRecFld (AmbiguousFieldOcc id) -- ^ Variable pointing to record selector

  | HsOverLabel FastString   -- ^ Overloaded label (See Note [Overloaded labels]
                             --   in GHC.OverloadedLabels)
  | HsIPVar   HsIPName       -- ^ Implicit parameter
  | HsOverLit (HsOverLit id) -- ^ Overloaded literals

  | HsLit     HsLit          -- ^ Simple (non-overloaded) literals

  | HsLam     (MatchGroup id (LHsExpr id)) -- ^ Lambda abstraction. Currently always a single match
       --
       -- - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnLam',
       --       'ApiAnnotation.AnnRarrow',

       -- For details on above see note [Api annotations] in ApiAnnotation

  | HsLamCase (MatchGroup id (LHsExpr id)) -- ^ Lambda-case
       --
       -- - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnLam',
       --           'ApiAnnotation.AnnCase','ApiAnnotation.AnnOpen',
       --           'ApiAnnotation.AnnClose'

       -- For details on above see note [Api annotations] in ApiAnnotation

  | HsApp     (LHsExpr id) (LHsExpr id) -- ^ Application

  | HsAppType (LHsExpr id) (LHsWcType id) -- ^ Visible type application
       --
       -- Explicit type argument; e.g  f @Int x y
       -- NB: Has wildcards, but no implicit quantification
       --
       -- - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnAt',



  -- | Operator applications:
  -- NB Bracketed ops such as (+) come out as Vars.

  -- NB We need an expr for the operator in an OpApp/Section since
  -- the typechecker may need to apply the operator to a few types.

  | OpApp       (LHsExpr id)    -- left operand
                (LHsExpr id)    -- operator
                (LHsExpr id)    -- right operand

  -- | Negation operator. Contains the negated expression and the name
  -- of 'negate'
  --
  --  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnMinus'

  -- For details on above see note [Api annotations] in ApiAnnotation
  | NegApp      (LHsExpr id)

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'('@,
  --             'ApiAnnotation.AnnClose' @')'@

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsPar       (LHsExpr id)    -- ^ Parenthesised expr; see Note [Parens in HsSyn]

  | SectionL    (LHsExpr id)    -- operand; see Note [Sections in HsSyn]
                (LHsExpr id)    -- operator
  | SectionR    (LHsExpr id)    -- operator; see Note [Sections in HsSyn]
                (LHsExpr id)    -- operand

  -- | Used for explicit tuples and sections thereof
  --
  --  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen',
  --         'ApiAnnotation.AnnClose'

  -- For details on above see note [Api annotations] in ApiAnnotation
  | ExplicitTuple
        [LHsTupArg id]
        Boxity

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnCase',
  --       'ApiAnnotation.AnnOf','ApiAnnotation.AnnOpen' @'{'@,
  --       'ApiAnnotation.AnnClose' @'}'@

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsCase      (LHsExpr id)
                (MatchGroup id (LHsExpr id))

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnIf',
  --       'ApiAnnotation.AnnSemi',
  --       'ApiAnnotation.AnnThen','ApiAnnotation.AnnSemi',
  --       'ApiAnnotation.AnnElse',

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsIf        (LHsExpr id)    --  predicate
                (LHsExpr id)    --  then part
                (LHsExpr id)    --  else part

  -- | Multi-way if
  --
  -- - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnIf'
  --       'ApiAnnotation.AnnOpen','ApiAnnotation.AnnClose',

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsMultiIf [LGRHS id (LHsExpr id)]

  -- | let(rec)
  --
  -- - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnLet',
  --       'ApiAnnotation.AnnOpen' @'{'@,
  --       'ApiAnnotation.AnnClose' @'}'@,'ApiAnnotation.AnnIn'

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsLet       (Located (HsLocalBinds id))
                (LHsExpr  id)

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnDo',
  --             'ApiAnnotation.AnnOpen', 'ApiAnnotation.AnnSemi',
  --             'ApiAnnotation.AnnVbar',
  --             'ApiAnnotation.AnnClose'

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsDo        (HsStmtContext id)     -- The parameterisation is unimportant
                                         -- because in this context we never use
                                         -- the PatGuard or ParStmt variant
                (Located [ExprLStmt id]) -- "do":one or more stmts

  -- | Syntactic list: [a,b,c,...]
  --
  --  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'['@,
  --              'ApiAnnotation.AnnClose' @']'@

  -- For details on above see note [Api annotations] in ApiAnnotation
  | ExplicitList [LHsExpr id]

  -- | Syntactic parallel array: [:e1, ..., en:]
  --
  --  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'[:'@,
  --              'ApiAnnotation.AnnDotdot','ApiAnnotation.AnnComma',
  --              'ApiAnnotation.AnnVbar'
  --              'ApiAnnotation.AnnClose' @':]'@

  -- For details on above see note [Api annotations] in ApiAnnotation
  | ExplicitPArr [LHsExpr id]

  -- | Record construction
  --
  --  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'{'@,
  --         'ApiAnnotation.AnnDotdot','ApiAnnotation.AnnClose' @'}'@

  -- For details on above see note [Api annotations] in ApiAnnotation
  | RecordCon
      { rcon_con_name :: Located id         -- The constructor name;
                                            --  not used after type checking
      , rcon_flds     :: HsRecordBinds id } -- The fields

  -- | Record update
  --
  --  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'{'@,
  --         'ApiAnnotation.AnnDotdot','ApiAnnotation.AnnClose' @'}'@

  -- For details on above see note [Api annotations] in ApiAnnotation
  | RecordUpd
      { rupd_expr :: LHsExpr id
      , rupd_flds :: [LHsRecUpdField id]
      }
  -- For a type family, the arg types are of the *instance* tycon,
  -- not the family tycon

  -- | Expression with an explicit type signature. @e :: type@
  --
  --  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnDcolon'

  -- For details on above see note [Api annotations] in ApiAnnotation
  | ExprWithTySig
                (LHsExpr id)
                (LHsSigWcType id)


  -- | Arithmetic sequence
  --
  --  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'['@,
  --              'ApiAnnotation.AnnComma','ApiAnnotation.AnnDotdot',
  --              'ApiAnnotation.AnnClose' @']'@

  -- For details on above see note [Api annotations] in ApiAnnotation
  | ArithSeq (ArithSeqInfo id)

  -- | Arithmetic sequence for parallel array
  --
  -- > [:e1..e2:] or [:e1, e2..e3:]
  --
  --  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'[:'@,
  --              'ApiAnnotation.AnnComma','ApiAnnotation.AnnDotdot',
  --              'ApiAnnotation.AnnVbar',
  --              'ApiAnnotation.AnnClose' @':]'@

  -- For details on above see note [Api annotations] in ApiAnnotation
  | PArrSeq (ArithSeqInfo id)

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'{-\# SCC'@,
  --             'ApiAnnotation.AnnVal' or 'ApiAnnotation.AnnValStr',
  --              'ApiAnnotation.AnnClose' @'\#-}'@

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsSCC       SourceText            -- Note [Pragma source text] in BasicTypes
                StringLiteral         -- "set cost centre" SCC pragma
                (LHsExpr id)          -- expr whose cost is to be measured

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'{-\# CORE'@,
  --             'ApiAnnotation.AnnVal', 'ApiAnnotation.AnnClose' @'\#-}'@

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsCoreAnn   SourceText            -- Note [Pragma source text] in BasicTypes
                StringLiteral         -- hdaume: core annotation
                (LHsExpr id)

  -----------------------------------------------------------
  -- MetaHaskell Extensions

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen',
  --         'ApiAnnotation.AnnOpen','ApiAnnotation.AnnClose',
  --         'ApiAnnotation.AnnClose'

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsBracket    (HsBracket id)

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen',
  --         'ApiAnnotation.AnnClose'

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsSpliceE  (HsSplice id)

  -----------------------------------------------------------
  -- Arrow notation extension

  -- | @proc@ notation for Arrows
  --
  --  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnProc',
  --          'ApiAnnotation.AnnRarrow'

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsProc      (LPat id)               -- arrow abstraction, proc
                (LHsCmdTop id)          -- body of the abstraction
                                        -- always has an empty stack

  ---------------------------------------
  -- static pointers extension
  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnStatic',

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsStatic (LHsExpr id)        -- Body

  ---------------------------------------
  -- The following are commands, not expressions proper
  -- They are only used in the parsing stage and are removed
  --    immediately in parser.RdrHsSyn.checkCommand

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.Annlarrowtail',
  --          'ApiAnnotation.Annrarrowtail','ApiAnnotation.AnnLarrowtail',
  --          'ApiAnnotation.AnnRarrowtail'

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsArrApp             -- Arrow tail, or arrow application (f -< arg)
        (LHsExpr id)     -- arrow expression, f
        (LHsExpr id)     -- input expression, arg
        HsArrAppType     -- higher-order (-<<) or first-order (-<)
        Bool             -- True => right-to-left (f -< arg)
                         -- False => left-to-right (arg >- f)

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'(|'@,
  --         'ApiAnnotation.AnnClose' @'|)'@

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsArrForm            -- Command formation,  (| e cmd1 .. cmdn |)
        (LHsExpr id)     -- the operator
                         -- after type-checking, a type abstraction to be
                         -- applied to the type of the local environment tuple
        (Maybe Fixity)   -- fixity (filled in by the renamer), for forms that
                         -- were converted from OpApp's by the renamer
        [LHsCmdTop id]   -- argument commands

  ---------------------------------------
  -- Haskell program coverage (Hpc) Support

  | HsBinTick
     Int                                -- module-local tick number for True
     Int                                -- module-local tick number for False
     (LHsExpr id)                       -- sub-expression

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen',
  --       'ApiAnnotation.AnnOpen' @'{-\# GENERATED'@,
  --       'ApiAnnotation.AnnVal','ApiAnnotation.AnnVal',
  --       'ApiAnnotation.AnnColon','ApiAnnotation.AnnVal',
  --       'ApiAnnotation.AnnMinus',
  --       'ApiAnnotation.AnnVal','ApiAnnotation.AnnColon',
  --       'ApiAnnotation.AnnVal',
  --       'ApiAnnotation.AnnClose' @'\#-}'@

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsTickPragma                      -- A pragma introduced tick
     SourceText                       -- Note [Pragma source text] in BasicTypes
     (StringLiteral,(Int,Int),(Int,Int))
                                      -- external span for this tick
     ((SourceText,SourceText),(SourceText,SourceText))
        -- Source text for the four integers used in the span.
        -- See note [Pragma source text] in BasicTypes
     (LHsExpr id)

  ---------------------------------------
  -- These constructors only appear temporarily in the parser.
  -- The renamer translates them into the Right Thing.

  | EWildPat                 -- wildcard

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnAt'

  -- For details on above see note [Api annotations] in ApiAnnotation
  | EAsPat      (Located id) -- as pattern
                (LHsExpr id)

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnRarrow'

  -- For details on above see note [Api annotations] in ApiAnnotation
  | EViewPat    (LHsExpr id) -- view pattern
                (LHsExpr id)

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnTilde'

  -- For details on above see note [Api annotations] in ApiAnnotation
  | ELazyPat    (LHsExpr id) -- ~ pattern

deriving instance (Data id) => Data (HsExpr id)

-- | HsTupArg is used for tuple sections
--  (,a,) is represented by  ExplicitTuple [Missing ty1, Present a, Missing ty3]
--  Which in turn stands for (\x:ty1 \y:ty2. (x,a,y))
type LHsTupArg id = Located (HsTupArg id)
-- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnComma'

-- For details on above see note [Api annotations] in ApiAnnotation
data HsTupArg id
  = Present (LHsExpr id)     -- ^ The argument
  | Missing
deriving instance (Data id) => Data (HsTupArg id)

{-
************************************************************************
*                                                                      *
\subsection{Commands (in arrow abstractions)}
*                                                                      *
************************************************************************

We re-use HsExpr to represent these.
-}

type LHsCmd id = Located (HsCmd id)

data HsCmd id
  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.Annlarrowtail',
  --          'ApiAnnotation.Annrarrowtail','ApiAnnotation.AnnLarrowtail',
  --          'ApiAnnotation.AnnRarrowtail'

  -- For details on above see note [Api annotations] in ApiAnnotation
  = HsCmdArrApp          -- Arrow tail, or arrow application (f -< arg)
        (LHsExpr id)     -- arrow expression, f
        (LHsExpr id)     -- input expression, arg
        HsArrAppType     -- higher-order (-<<) or first-order (-<)
        Bool             -- True => right-to-left (f -< arg)
                         -- False => left-to-right (arg >- f)

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'(|'@,
  --         'ApiAnnotation.AnnClose' @'|)'@

  -- For details on above see note [Api annotations] in ApiAnnotation
  | HsCmdArrForm         -- Command formation,  (| e cmd1 .. cmdn |)
        (LHsExpr id)     -- the operator
                         -- after type-checking, a type abstraction to be
                         -- applied to the type of the local environment tuple
        (Maybe Fixity)   -- fixity (filled in by the renamer), for forms that
                         -- were converted from OpApp's by the renamer
        [LHsCmdTop id]   -- argument commands

  | HsCmdApp    (LHsCmd id)
                (LHsExpr id)

  | HsCmdLam    (MatchGroup id (LHsCmd id))     -- kappa
       -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnLam',
       --       'ApiAnnotation.AnnRarrow',

       -- For details on above see note [Api annotations] in ApiAnnotation

  | HsCmdPar    (LHsCmd id)                     -- parenthesised command
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnOpen' @'('@,
    --             'ApiAnnotation.AnnClose' @')'@

    -- For details on above see note [Api annotations] in ApiAnnotation

  | HsCmdCase   (LHsExpr id)
                (MatchGroup id (LHsCmd id))     -- bodies are HsCmd's
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnCase',
    --       'ApiAnnotation.AnnOf','ApiAnnotation.AnnOpen' @'{'@,
    --       'ApiAnnotation.AnnClose' @'}'@

    -- For details on above see note [Api annotations] in ApiAnnotation

  | HsCmdIf     (LHsExpr id)                    -- predicate
                (LHsCmd id)                     -- then part
                (LHsCmd id)                     -- else part
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnIf',
    --       'ApiAnnotation.AnnSemi',
    --       'ApiAnnotation.AnnThen','ApiAnnotation.AnnSemi',
    --       'ApiAnnotation.AnnElse',

    -- For details on above see note [Api annotations] in ApiAnnotation

  | HsCmdLet    (Located (HsLocalBinds id))      -- let(rec)
                (LHsCmd  id)
    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnLet',
    --       'ApiAnnotation.AnnOpen' @'{'@,
    --       'ApiAnnotation.AnnClose' @'}'@,'ApiAnnotation.AnnIn'

    -- For details on above see note [Api annotations] in ApiAnnotation

  | HsCmdDo     (Located [CmdLStmt id])

    -- ^ - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnDo',
    --             'ApiAnnotation.AnnOpen', 'ApiAnnotation.AnnSemi',
    --             'ApiAnnotation.AnnVbar',
    --             'ApiAnnotation.AnnClose'

    -- For details on above see note [Api annotations] in ApiAnnotation

deriving instance (Data id) => Data (HsCmd id)

data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp
  deriving Data


{- | Top-level command, introducing a new arrow.
This may occur inside a proc (where the stack is empty) or as an
argument of a command-forming operator.
-}

type LHsCmdTop id = Located (HsCmdTop id)

data HsCmdTop id
  = HsCmdTop (LHsCmd id)
deriving instance (Data id) => Data (HsCmdTop id)

{-
************************************************************************
*                                                                      *
\subsection{Record binds}
*                                                                      *
************************************************************************
-}

type HsRecordBinds id = HsRecFields id (LHsExpr id)

{-
************************************************************************
*                                                                      *
\subsection{@Match@, @GRHSs@, and @GRHS@ datatypes}
*                                                                      *
************************************************************************

@Match@es are sets of pattern bindings and right hand sides for
functions, patterns or case branches. For example, if a function @g@
is defined as:
\begin{verbatim}
g (x,y) = y
g ((x:ys),y) = y+1,
\end{verbatim}
then \tr{g} has two @Match@es: @(x,y) = y@ and @((x:ys),y) = y+1@.

It is always the case that each element of an @[Match]@ list has the
same number of @pats@s inside it.  This corresponds to saying that
a function defined by pattern matching must have the same number of
patterns in each equation.
-}

data MatchGroup id body
  = MG { mg_alts    :: Located [LMatch id body]  -- The alternatives
       , mg_origin  :: Origin }
     -- The type is the type of the entire group
     --      t1 -> ... -> tn -> tr
     -- where there are n patterns
deriving instance (Data body,Data id) => Data (MatchGroup id body)

type LMatch id body = Located (Match id body)
-- ^ May have 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnSemi' when in a
--   list

-- For details on above see note [Api annotations] in ApiAnnotation
data Match id body
  = Match {
        m_ctxt :: HsMatchContext ( id),
          -- See note [m_ctxt in Match]
        m_pats :: [LPat id], -- The patterns
        m_type :: (Maybe (LHsType id)),
                                 -- A type signature for the result of the match
                                 -- Nothing after typechecking
                                 -- NB: No longer supported
        m_grhss :: (GRHSs id body)
  }
deriving instance (Data body,Data id) => Data (Match id body)

-- For details on above see note [Api annotations] in ApiAnnotation
data GRHSs id body
  = GRHSs {
      grhssGRHSs :: [LGRHS id body],       -- ^ Guarded RHSs
      grhssLocalBinds :: Located (HsLocalBinds id) -- ^ The where clause
    }
deriving instance (Data body,Data id) => Data (GRHSs id body)

type LGRHS id body = Located (GRHS id body)

-- | Guarded Right Hand Side.
data GRHS id body = GRHS [GuardLStmt id] -- Guards
                         body            -- Right hand side
deriving instance (Data body,Data id) => Data (GRHS id body)

{-
************************************************************************
*                                                                      *
\subsection{Do stmts and list comprehensions}
*                                                                      *
************************************************************************
-}

type LStmt id body = Located (StmtLR id id body)
type LStmtLR idL idR body = Located (StmtLR idL idR body)

type Stmt id body = StmtLR id id body

type CmdLStmt   id = LStmt id (LHsCmd  id)
type CmdStmt    id = Stmt  id (LHsCmd  id)
type ExprLStmt  id = LStmt id (LHsExpr id)
type ExprStmt   id = Stmt  id (LHsExpr id)

type GuardLStmt id = LStmt id (LHsExpr id)

-- The SyntaxExprs in here are used *only* for do-notation and monad
-- comprehensions, which have rebindable syntax. Otherwise they are unused.
-- | API Annotations when in qualifier lists or guards
--  - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnVbar',
--         'ApiAnnotation.AnnComma','ApiAnnotation.AnnThen',
--         'ApiAnnotation.AnnBy','ApiAnnotation.AnnBy',
--         'ApiAnnotation.AnnGroup','ApiAnnotation.AnnUsing'

-- For details on above see note [Api annotations] in ApiAnnotation
data StmtLR idL idR body -- body should always be (LHs**** idR)
  = LastStmt  -- Always the last Stmt in ListComp, MonadComp, PArrComp,
              -- and (after the renamer) DoExpr, MDoExpr
              -- Not used for GhciStmtCtxt, PatGuard, which scope over other stuff
          body
          Bool               -- True <=> return was stripped by ApplicativeDo

  -- For details on above see note [Api annotations] in ApiAnnotation
  | BindStmt (LPat idL)
             body

  | BodyStmt body              -- See Note [BodyStmt]

  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnLet'
  --          'ApiAnnotation.AnnOpen' @'{'@,'ApiAnnotation.AnnClose' @'}'@,

  -- For details on above see note [Api annotations] in ApiAnnotation
  | LetStmt  (Located (HsLocalBindsLR idL idR))

  -- ParStmts only occur in a list/monad comprehension
  | ParStmt  [ParStmtBlock idL idR]

  | TransStmt {
      trS_form  :: TransForm,
      trS_stmts :: [ExprLStmt idL],   -- Stmts to the *left* of the 'group'
                                      -- which generates the tuples to be grouped

      trS_bndrs :: [(idR, idR)],      -- See Note [TransStmt binder map]

      trS_using :: LHsExpr idR,
      trS_by :: Maybe (LHsExpr idR)  -- "by e" (optional)
        -- Invariant: if trS_form = GroupBy, then grp_by = Just e

    }                                 -- See Note [Monad Comprehensions]

  -- Recursive statement (see Note [How RecStmt works] below)
  -- | - 'ApiAnnotation.AnnKeywordId' : 'ApiAnnotation.AnnRec'

  -- For details on above see note [Api annotations] in ApiAnnotation
  | RecStmt
     { recS_stmts :: [LStmtLR idL idR body]

        -- The next two fields are only valid after renaming
     , recS_later_ids :: [idR] -- The ids are a subset of the variables bound by the
                               -- stmts that are used in stmts that follow the RecStmt

     , recS_rec_ids :: [idR]   -- Ditto, but these variables are the "recursive" ones,
                               -- that are used before they are bound in the stmts of
                               -- the RecStmt.
        -- An Id can be in both groups
        -- Both sets of Ids are (now) treated monomorphically
        -- See Note [How RecStmt works] for why they are separate
      }
deriving instance (Data body, Data idL, Data idR)
  => Data (StmtLR idL idR body)

data TransForm   -- The 'f' below is the 'using' function, 'e' is the by function
  = ThenForm     -- then f               or    then f by e             (depending on trS_by)
  | GroupForm    -- then group using f   or    then group by e using f (depending on trS_by)
  deriving Data

data ParStmtBlock idL idR
  = ParStmtBlock
        [ExprLStmt idL]
        [idR]              -- The variables to be returned
deriving instance (Data idL, Data idR) => Data (ParStmtBlock idL idR)

data ApplicativeArg idL idR
  = ApplicativeArgOne            -- pat <- expr (pat must be irrefutable)
      (LPat idL)
      (LHsExpr idL)
  | ApplicativeArgMany           -- do { stmts; return vars }
      [ExprLStmt idL]            -- stmts
      (HsExpr idL)               -- return (v1,..,vn), or just (v1,..,vn)
      (LPat idL)                 -- (v1,...,vn)
deriving instance (Data idL, Data idR) => Data (ApplicativeArg idL idR)

{-
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 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'
       and used either in the 'by' clause,
                or     in the stmts following the 'group'
    Each item is a pair of identical variables.

  * After typechecking:
          [ (x27:Int, x27:[Int]), ..., (z35:Bool, z35:[Bool]) ]
    Each pair has the same unique, but different *types*.

Note [BodyStmt]
~~~~~~~~~~~~~~~
BodyStmts are a bit tricky, because what they mean
depends on the context.  Consider the following contexts:

        A do expression of type (m res_ty)
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        * BodyStmt E any_ty:   do { ....; E; ... }
                E :: m any_ty
          Translation: E >> ...

        A list comprehensions of type [elt_ty]
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        * BodyStmt E Bool:   [ .. | .... E ]
                        [ .. | ..., E, ... ]
                        [ .. | .... | ..., E | ... ]
                E :: Bool
          Translation: if E then fail else ...

        A guard list, guarding a RHS of type rhs_ty
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        * BodyStmt E BooParStmtBlockl:   f x | ..., E, ... = ...rhs...
                E :: Bool
          Translation: if E then fail else ...

        A monad comprehension of type (m res_ty)
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        * BodyStmt E Bool:   [ .. | .... E ]
                E :: Bool
          Translation: guard E >> ...

Array comprehensions are handled like list comprehensions.

Note [How RecStmt works]
~~~~~~~~~~~~~~~~~~~~~~~~
Example:
   HsDo [ BindStmt x ex

        , RecStmt { recS_rec_ids   = [a, c]
                  , recS_stmts     = [ BindStmt b (return (a,c))
                                     , LetStmt a = ...b...
                                     , BindStmt c ec ]
                  , recS_later_ids = [a, b]

        , return (a b) ]

Here, the RecStmt binds a,b,c; but
  - Only a,b are used in the stmts *following* the RecStmt,
  - Only a,c are used in the stmts *inside* the RecStmt
        *before* their bindings

Why do we need *both* rec_ids and later_ids?  For monads they could be
combined into a single set of variables, but not for arrows.  That
follows from the types of the respective feedback operators:

        mfix :: MonadFix m => (a -> m a) -> m a
        loop :: ArrowLoop a => a (b,d) (c,d) -> a b c

* For mfix, the 'a' covers the union of the later_ids and the rec_ids
* For 'loop', 'c' is the later_ids and 'd' is the rec_ids

Note [Typing a RecStmt]
~~~~~~~~~~~~~~~~~~~~~~~
A (RecStmt stmts) types as if you had written

  (v1,..,vn, _, ..., _) <- mfix (\~(_, ..., _, r1, ..., rm) ->
                                 do { stmts
                                    ; return (v1,..vn, r1, ..., rm) })

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 ]

BodyStmts require the 'Control.Monad.guard' function for boolean
expressions:

  [ body | exp, stmts ]
   =>
  guard exp >> [ body | stmts ]

Parallel statements require the 'Control.Monad.Zip.mzip' function:

  [ 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.
-}

{-
************************************************************************
*                                                                      *
                Template Haskell quotation brackets
*                                                                      *
************************************************************************
-}

data HsSplice id
   = HsNativSplice       --  $n(f 4)
        id               -- A unique name to identify this splice point
        (LHsExpr id)     -- See Note [Pending Splices]

   | HsTypedSplice       --  $$z  or $$(f 4)
        id               -- A unique name to identify this splice point
        (LHsExpr id)     -- See Note [Pending Splices]

   | HsUntypedSplice     --  $z  or $(f 4)
        id               -- A unique name to identify this splice point
        (LHsExpr id)     -- See Note [Pending Splices]

   | HsQuasiQuote        -- See Note [Quasi-quote overview] in TcSplice
        id               -- Splice point
        id               -- Quoter
        SrcSpan          -- The span of the enclosed string
        FastString       -- The enclosed string

deriving instance (Data id) => Data (HsSplice id)

data UntypedSpliceFlavour
  = UntypedExpSplice
  | UntypedPatSplice
  | UntypedTypeSplice
  | UntypedDeclSplice
  deriving Data

{-
Note [Pending Splices]
~~~~~~~~~~~~~~~~~~~~~~
When we rename an untyped bracket, we name and lift out all the nested
splices, so that when the typechecker hits the bracket, it can
typecheck those nested splices without having to walk over the untyped
bracket code.  So for example
    [| f $(g x) |]
looks like

    HsBracket (HsApp (HsVar "f") (HsSpliceE _ (g x)))

which the renamer rewrites to

    HsRnBracketOut (HsApp (HsVar f) (HsSpliceE sn (g x)))
                   [PendingRnSplice UntypedExpSplice sn (g x)]

* The 'sn' is the Name of the splice point, the SplicePointName

* The PendingRnExpSplice gives the splice that splice-point name maps to;
  and the typechecker can now conveniently find these sub-expressions

* The other copy of the splice, in the second argument of HsSpliceE
                                in the renamed first arg of HsRnBracketOut
  is used only for pretty printing

There are four varieties of pending splices generated by the renamer,
distinguished by their UntypedSpliceFlavour

 * Pending expression splices (UntypedExpSplice), e.g.,
       [|$(f x) + 2|]

   UntypedExpSplice is also used for
     * quasi-quotes, where the pending expression expands to
          $(quoter "...blah...")
       (see RnSplice.makePending, HsQuasiQuote case)

     * cross-stage lifting, where the pending expression expands to
          $(lift x)
       (see RnSplice.checkCrossStageLifting)

 * Pending pattern splices (UntypedPatSplice), e.g.,
       [| \$(f x) -> x |]

 * Pending type splices (UntypedTypeSplice), e.g.,
       [| f :: $(g x) |]

 * Pending declaration (UntypedDeclSplice), e.g.,
       [| let $(f x) in ... |]

There is a fifth variety of pending splice, which is generated by the type
checker:

  * Pending *typed* expression splices, (PendingTcSplice), e.g.,
        [||1 + $$(f 2)||]

It would be possible to eliminate HsRnBracketOut and use HsBracketOut for the
output of the renamer. However, when pretty printing the output of the renamer,
e.g., in a type error message, we *do not* want to print out the pending
splices. In contrast, when pretty printing the output of the type checker, we
*do* want to print the pending splices. So splitting them up seems to make
sense, although I hate to add another constructor to HsExpr.
-}


data HsBracket id = ExpBr (LHsExpr id)   -- [|  expr  |]
                  | PatBr (LPat id)      -- [p| pat   |]
                  | DecBrL [LHsDecl id]  -- [d| decls |]; result of parser
                  | DecBrG (HsGroup id)  -- [d| decls |]; result of renamer
                  | TypBr (LHsType id)   -- [t| type  |]
                  | VarBr Bool id        -- True: 'x, False: ''T
                                         -- (The Bool flag is used only in pprHsBracket)
                  | TExpBr (LHsExpr id)  -- [||  expr  ||]
                  | NativBr (LHsExpr id)  -- [n|  expr  |]
deriving instance (Data id) => Data (HsBracket id)

{-
************************************************************************
*                                                                      *
\subsection{Enumerations and list comprehensions}
*                                                                      *
************************************************************************
-}

data ArithSeqInfo id
  = From            (LHsExpr id)
  | FromThen        (LHsExpr id)
                    (LHsExpr id)
  | FromTo          (LHsExpr id)
                    (LHsExpr id)
  | FromThenTo      (LHsExpr id)
                    (LHsExpr id)
                    (LHsExpr id)
deriving instance (Data id) => Data (ArithSeqInfo id)

{-
************************************************************************
*                                                                      *
\subsection{HsMatchCtxt}
*                                                                      *
************************************************************************
-}

data FunctionFixity = Prefix | Infix deriving (Typeable,Data,Eq)

-- | Context of a Match
data HsMatchContext id
  = FunRhs (Located id) FunctionFixity -- ^Function binding for f, fixity
  | LambdaExpr                  -- ^Patterns of a lambda
  | CaseAlt                     -- ^Patterns and guards on a case alternative
  | IfAlt                       -- ^Guards of a multi-way if alternative
  | ProcExpr                    -- ^Patterns of a proc
  | 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, list comprehension,
                                -- pattern guard, etc

  | ThPatSplice            -- ^A Template Haskell pattern splice
  | ThPatQuote             -- ^A Template Haskell pattern quotation [p| (a,b) |]
  | PatSyn                 -- ^A pattern synonym declaration
  deriving Functor
deriving instance (Data id) => Data (HsMatchContext id)

data HsStmtContext id
  = ListComp
  | MonadComp
  | PArrComp                         -- ^Parallel array comprehension

  | DoExpr                           -- ^do { ... }
  | MDoExpr                          -- ^mdo { ... }  ie recursive do-expression
  | ArrowExpr                        -- ^do-notation in an arrow-command context

  | GhciStmtCtxt                     -- ^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
  | TransStmtCtxt (HsStmtContext id) -- ^A branch of a transform stmt
  deriving Functor
deriving instance (Data id) => Data (HsStmtContext id)
