    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Language.Haskell.Exts.Build
    -- Copyright   :  (c) The GHC Team, 1997-2000,
    --                (c) Niklas Broberg 2004
    -- License     :  BSD-style (see the file LICENSE.txt)
    --
    -- Maintainer  :  Niklas Broberg, d00nibro@chalmers.se
    -- Stability   :  experimental
    -- Portability :  portable
    --
    -- This module contains combinators to use when building
    -- Haskell source trees programmatically, as opposed to
    -- parsing them from a string. The contents here are quite
    -- experimental and will likely receive a lot of attention
    -- when the rest has stabilised.
    --
    -----------------------------------------------------------------------------

    module Language.Haskell.Exts.Build (

        -- * Syntax building functions
        name,       -- :: String -> Name
        sym,        -- :: String -> Name
        var,        -- :: Name -> Exp
        op,         -- :: Name -> QOp
        qvar,       -- :: Module -> Name -> Exp
        pvar,       -- :: Name -> Pat
        app,        -- :: Exp -> Exp -> Exp
        infixApp,   -- :: Exp -> QOp -> Exp -> Exp
        appFun,     -- :: Exp -> [Exp] -> Exp
        pApp,       -- :: Name -> [Pat] -> Pat
        tuple,      -- :: [Exp] -> Exp
        pTuple,     -- :: [Pat] -> Pat
        varTuple,   -- :: [Name] -> Exp
        pvarTuple,  -- :: [Name] -> Pat
        function,   -- :: String -> Exp
        strE,       -- :: String -> Exp
        charE,      -- :: Char -> Exp
        intE,       -- :: Integer -> Exp
        strP,       -- :: String -> Pat
        charP,      -- :: Char -> Pat
        intP,       -- :: Integer -> Pat
        doE,        -- :: [Stmt] -> Exp
        lamE,       -- :: SrcLoc -> [Pat] -> Exp -> Exp
        letE,       -- :: [Decl] -> Exp -> Exp
        caseE,      -- :: Exp -> [Alt] -> Exp
        alt,        -- :: SrcLoc -> Pat -> Exp -> Alt
        altGW,      -- :: SrcLoc -> Pat -> [Stmt] -> Exp -> Binds -> Alt
        listE,      -- :: [Exp] -> Exp
        eList,      -- :: Exp
        peList,     -- :: Pat
        paren,      -- :: Exp -> Exp
        pParen,     -- :: Pat -> Pat
        qualStmt,   -- :: Exp -> Stmt
        genStmt,    -- :: SrcLoc -> Pat -> Exp -> Stmt
        letStmt,    -- :: [Decl] -> Stmt
        binds,      -- :: [Decl] -> Binds
        noBinds,    -- :: Binds
        wildcard,   -- :: Pat
        genNames,   -- :: String -> Int -> [Name]

        -- * More advanced building
        sfun,           -- :: SrcLoc -> Name -> [Name] -> Rhs -> Binds -> Decl
        simpleFun,      -- :: SrcLoc -> Name -> Name -> Exp -> Decl
        patBind,        -- :: SrcLoc -> Pat -> Exp -> Decl
        patBindWhere,   -- :: SrcLoc -> Pat -> Exp -> [Decl] -> Decl
        nameBind,       -- :: SrcLoc -> Name -> Exp -> Decl
        metaFunction,   -- :: String -> [Exp] -> Exp
        metaConPat      -- :: String -> [Pat] -> Pat
      ) where

    import Language.Haskell.Exts.Syntax

    -----------------------------------------------------------------------------
    -- Help functions for Abstract syntax

    -- | An identifier with the given string as its name.
    --   The string should be a valid Haskell identifier.
    name :: String -> Name
    name = Ident

    -- | A symbol identifier. The string should be a valid
    --   Haskell symbol identifier.
    sym :: String -> Name
    sym = Symbol

    -- | A local variable as expression.
    var :: Name -> Exp
    var = Var . UnQual

    -- | Use the given identifier as an operator.
    op :: Name -> QOp
    op = QVarOp . UnQual

    -- | A qualified variable as expression.
    qvar :: ModuleName -> Name -> Exp
    qvar m n = Var $ Qual m n

    -- | A pattern variable.
    pvar :: Name -> Pat
    pvar = PVar

    -- | Application of expressions by juxtaposition.
    app :: Exp -> Exp -> Exp
    app = App

    -- | Apply an operator infix.
    infixApp :: Exp -> QOp -> Exp -> Exp
    infixApp = InfixApp

    -- | Apply a function to a list of arguments.
    appFun :: Exp -> [Exp] -> Exp
    appFun f [] = f
    appFun f (a:as) = appFun (app f a) as

    -- | A constructor pattern, with argument patterns.
    pApp :: Name -> [Pat] -> Pat
    pApp n ps = PApp (UnQual n) ps

    -- | A tuple expression.
    tuple :: [Exp] -> Exp
    tuple = Tuple

    -- | A tuple pattern.
    pTuple :: [Pat] -> Pat
    pTuple = PTuple

    -- | A tuple expression consisting of variables only.
    varTuple :: [Name] -> Exp
    varTuple ns = tuple $ map var ns

    -- | A tuple pattern consisting of variables only.
    pvarTuple :: [Name] -> Pat
    pvarTuple ns = pTuple $ map pvar ns

    -- | A function with a given name.
    function :: String -> Exp
    function = var . Ident

    -- | A literal string expression.
    strE :: String -> Exp
    strE = Lit . String

    -- | A literal character expression.
    charE :: Char -> Exp
    charE = Lit . Char

    -- | A literal integer expression.
    intE :: Integer -> Exp
    intE = Lit . Int

    -- | A literal string pattern.
    strP :: String -> Pat
    strP = PLit . String

    -- | A literal character pattern.
    charP :: Char -> Pat
    charP = PLit . Char

    -- | A literal integer pattern.
    intP :: Integer -> Pat
    intP = PLit . Int

    -- | A do block formed by the given statements.
    --   The last statement in the list should be
    --   a 'Qualifier' expression.
    doE :: [Stmt] -> Exp
    doE = Do

    -- | Lambda abstraction, given a list of argument
    --   patterns and an expression body.
    lamE :: SrcLoc -> [Pat] -> Exp -> Exp
    lamE = Lambda

    -- | A @let@ ... @in@ block.
    letE :: [Decl] -> Exp -> Exp
    letE ds e = Let (binds ds) e

    -- | A @case@ expression.
    caseE :: Exp -> [Alt] -> Exp
    caseE = Case

    -- | An unguarded alternative in a @case@ expression.
    alt :: SrcLoc -> Pat -> Exp -> Alt
    alt s p e = Alt s p (unGAlt e) noBinds

    -- | An alternative with a single guard in a @case@ expression.
    altGW :: SrcLoc -> Pat -> [Stmt] -> Exp -> Binds -> Alt
    altGW s p gs e w = Alt s p (gAlt s gs e) w

    -- | An unguarded righthand side of a @case@ alternative.
    unGAlt :: Exp -> GuardedAlts
    unGAlt = UnGuardedAlt

    -- | An list of guarded righthand sides for a @case@ alternative.
    gAlts :: SrcLoc -> [([Stmt],Exp)] -> GuardedAlts
    gAlts s as = GuardedAlts $ map (\(gs,e) -> GuardedAlt s gs e) as

    -- | A single guarded righthand side for a @case@ alternative.
    gAlt :: SrcLoc -> [Stmt] -> Exp -> GuardedAlts
    gAlt s gs e = gAlts s [(gs,e)]

    -- | A list expression.
    listE :: [Exp] -> Exp
    listE = List

    -- | The empty list expression.
    eList :: Exp
    eList = List []

    -- | The empty list pattern.
    peList :: Pat
    peList = PList []

    -- | Put parentheses around an expression.
    paren :: Exp -> Exp
    paren = Paren

    -- | Put parentheses around a pattern.
    pParen :: Pat -> Pat
    pParen = PParen

    -- | A qualifier expression statement.
    qualStmt :: Exp -> Stmt
    qualStmt = Qualifier

    -- | A generator statement: /pat/ @<-@ /exp/
    genStmt :: SrcLoc -> Pat -> Exp -> Stmt
    genStmt = Generator

    -- | A @let@ binding group as a statement.
    letStmt :: [Decl] -> Stmt
    letStmt ds = LetStmt $ binds ds

    -- | Hoist a set of declarations to a binding group.
    binds :: [Decl] -> Binds
    binds = BDecls

    -- | An empty binding group.
    noBinds :: Binds
    noBinds = binds []

    -- | The wildcard pattern: @_@
    wildcard :: Pat
    wildcard = PWildCard

    -- | Generate k names by appending numbers 1 through k to a given string.
    genNames :: String -> Int -> [Name]
    genNames s k = [ Ident $ s ++ show i | i <- [1..k] ]

    -------------------------------------------------------------------------------
    -- Some more specialised help functions

    -- | A function with a single clause
    sfun :: SrcLoc -> Name -> [Name] -> Rhs -> Binds -> Decl
    sfun s f pvs rhs bs = FunBind [Match s f (map pvar pvs) Nothing rhs bs]

    -- | A function with a single clause, a single argument, no guards
    -- and no where declarations
    simpleFun :: SrcLoc -> Name -> Name -> Exp -> Decl
    simpleFun s f a e = let rhs = UnGuardedRhs e
                 in sfun s f [a] rhs noBinds

    -- | A pattern bind where the pattern is a variable, and where
    -- there are no guards and no 'where' clause.
    patBind :: SrcLoc -> Pat -> Exp -> Decl
    patBind s p e = let rhs = UnGuardedRhs e
             in PatBind s p Nothing rhs noBinds

    -- | A pattern bind where the pattern is a variable, and where
    -- there are no guards, but with a 'where' clause.
    patBindWhere :: SrcLoc -> Pat -> Exp -> [Decl] -> Decl
    patBindWhere s p e ds = let rhs = UnGuardedRhs e
                 in PatBind s p Nothing rhs (binds ds)

    -- | Bind an identifier to an expression.
    nameBind :: SrcLoc -> Name -> Exp -> Decl
    nameBind s n e = patBind s (pvar n) e

    -- | Apply function of a given name to a list of arguments.
    metaFunction :: String -> [Exp] -> Exp
    metaFunction s es = mf s (reverse es)
      where mf s []     = var $ name s
            mf s (e:es) = app (mf s es) e

    -- | Apply a constructor of a given name to a list of pattern
    --   arguments, forming a constructor pattern.
    metaConPat :: String -> [Pat] -> Pat
    metaConPat s ps = pApp (name s) ps