Language/Haskell/TH/Ppr.hs

-- TH.Ppr contains a prettyprinter for the
-- Template Haskell datatypes

module Language.Haskell.TH.Ppr where
 -- All of the exports from this module should
 -- be "public" functions. The main module TH
 -- re-exports them all.

import Text.PrettyPrint.HughesPJ (render)
import Language.Haskell.TH.PprLib
import Language.Haskell.TH.Syntax
import Data.Char ( toLower )

nestDepth :: Int
nestDepth = 4

type Precedence = Int
appPrec, opPrec, noPrec :: Precedence
appPrec = 2 -- Argument of a function application
opPrec = 1 -- Argument of an infix operator
noPrec = 0 -- Others

parensIf :: Bool -> Doc -> Doc
parensIf True d = parens d
parensIf False d = d

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

pprint :: Ppr a => a -> String
pprint x = render $ to_HPJ_Doc $ ppr x

class Ppr a where
 ppr :: a -> Doc
 ppr_list :: [a] -> Doc
 ppr_list = vcat . map ppr

instance Ppr a => Ppr [a] where
 ppr x = ppr_list x

------------------------------
instance Ppr Name where
 ppr v = pprName v

------------------------------
instance Ppr Info where
 ppr (ClassI d) = ppr d
 ppr (TyConI d) = ppr d
 ppr (PrimTyConI name arity is_unlifted) 
 = text "Primitive"
	<+> (if is_unlifted then text "unlifted" else empty)
	<+> text "type construtor" <+> quotes (ppr name)
	<+> parens (text "arity" <+> int arity)
 ppr (ClassOpI v ty cls fix) 
 = text "Class op from" <+> ppr cls <> colon <+>
 vcat [ppr_sig v ty, pprFixity v fix]
 ppr (DataConI v ty tc fix) 
 = text "Constructor from" <+> ppr tc <> colon <+>
 vcat [ppr_sig v ty, pprFixity v fix]
 ppr (TyVarI v ty)
 = text "Type variable" <+> ppr v <+> equals <+> ppr ty
 ppr (VarI v ty mb_d fix) 
 = vcat [ppr_sig v ty, pprFixity v fix, 
 case mb_d of { Nothing -> empty; Just d -> ppr d }]

ppr_sig :: Name -> Type -> Doc
ppr_sig v ty = ppr v <+> text "::" <+> ppr ty

pprFixity :: Name -> Fixity -> Doc
pprFixity _ f | f == defaultFixity = empty
pprFixity v (Fixity i d) = ppr_fix d <+> int i <+> ppr v
 where ppr_fix InfixR = text "infixr"
 ppr_fix InfixL = text "infixl"
 ppr_fix InfixN = text "infix"


------------------------------
instance Ppr Exp where
 ppr = pprExp noPrec

pprInfixExp :: Exp -> Doc
pprInfixExp (VarE v) = pprName' Infix v
pprInfixExp (ConE v) = pprName' Infix v
pprInfixExp _ = error "Attempt to pretty-print non-variable or constructor in infix context!"

pprExp :: Precedence -> Exp -> Doc
pprExp _ (VarE v) = pprName' Applied v
pprExp _ (ConE c) = pprName' Applied c
pprExp i (LitE l) = pprLit i l
pprExp i (AppE e1 e2) = parensIf (i >= appPrec) $ pprExp opPrec e1
 <+> pprExp appPrec e2
pprExp i (InfixE (Just e1) op (Just e2))
 = parensIf (i >= opPrec) $ pprExp opPrec e1
 <+> pprInfixExp op
 <+> pprExp opPrec e2
pprExp _ (InfixE me1 op me2) = parens $ pprMaybeExp noPrec me1
 <+> pprInfixExp op
 <+> pprMaybeExp noPrec me2
pprExp i (LamE ps e) = parensIf (i > noPrec) $ char '\\' <> hsep (map (pprPat appPrec) ps)
 <+> text "->" <+> ppr e
pprExp _ (TupE es) = parens $ sep $ punctuate comma $ map ppr es
-- Nesting in Cond is to avoid potential problems in do statments
pprExp i (CondE guard true false)
 = parensIf (i > noPrec) $ sep [text "if" <+> ppr guard,
 nest 1 $ text "then" <+> ppr true,
 nest 1 $ text "else" <+> ppr false]
pprExp i (LetE ds e) = parensIf (i > noPrec) $ text "let" <+> ppr ds
 $$ text " in" <+> ppr e
pprExp i (CaseE e ms)
 = parensIf (i > noPrec) $ text "case" <+> ppr e <+> text "of"
 $$ nest nestDepth (ppr ms)
pprExp i (DoE ss) = parensIf (i > noPrec) $ text "do" <+> ppr ss
pprExp _ (CompE []) = error "Can't happen: pprExp (CompExp [])"
-- This will probably break with fixity declarations - would need a ';'
pprExp _ (CompE ss) = text "[" <> ppr s
 <+> text "|"
 <+> (sep $ punctuate comma $ map ppr ss')
 <> text "]"
 where s = last ss
 ss' = init ss
pprExp _ (ArithSeqE d) = ppr d
pprExp _ (ListE es) = brackets $ sep $ punctuate comma $ map ppr es
pprExp i (SigE e t) = parensIf (i > noPrec) $ ppr e <+> text "::" <+> ppr t
pprExp _ (RecConE nm fs) = ppr nm <> braces (pprFields fs)
pprExp _ (RecUpdE e fs) = pprExp appPrec e <> braces (pprFields fs)

pprFields :: [(Name,Exp)] -> Doc
pprFields = sep . punctuate comma . map (\(s,e) -> ppr s <+> equals <+> ppr e)

pprMaybeExp :: Precedence -> Maybe Exp -> Doc
pprMaybeExp _ Nothing = empty
pprMaybeExp i (Just e) = pprExp i e

------------------------------
instance Ppr Stmt where
 ppr (BindS p e) = ppr p <+> text "<-" <+> ppr e
 ppr (LetS ds) = text "let" <+> ppr ds
 ppr (NoBindS e) = ppr e
 ppr (ParS sss) = sep $ punctuate (text "|")
 $ map (sep . punctuate comma . map ppr) sss

------------------------------
instance Ppr Match where
 ppr (Match p rhs ds) = ppr p <+> pprBody False rhs
 $$ where_clause ds

------------------------------
pprBody :: Bool -> Body -> Doc
pprBody eq (GuardedB xs) = nest nestDepth $ vcat $ map do_guard xs
 where eqd = if eq then text "=" else text "->"
 do_guard (NormalG g, e) = text "|" <+> ppr g <+> eqd <+> ppr e
 do_guard (PatG ss, e) = text "|" <+> vcat (map ppr ss)
 $$ nest nestDepth (eqd <+> ppr e)
pprBody eq (NormalB e) = (if eq then text "=" else text "->") <+> ppr e

------------------------------
pprLit :: Precedence -> Lit -> Doc
pprLit i (IntPrimL x) = parensIf (i > noPrec && x < 0)
 (integer x <> char '#')
pprLit _ (WordPrimL x) = integer x <> text "##"
pprLit i (FloatPrimL x) = parensIf (i > noPrec && x < 0)
 (float (fromRational x) <> char '#')
pprLit i (DoublePrimL x) = parensIf (i > noPrec && x < 0)
 (double (fromRational x) <> text "##")
pprLit i (IntegerL x) = parensIf (i > noPrec && x < 0) (integer x)
pprLit _ (CharL c) = text (show c)
pprLit _ (StringL s) = text (show s)
pprLit i (RationalL rat) = parensIf (i > noPrec) $ rational rat

------------------------------
instance Ppr Pat where
 ppr = pprPat noPrec

pprPat :: Precedence -> Pat -> Doc
pprPat i (LitP l) = pprLit i l
pprPat _ (VarP v) = pprName' Applied v
pprPat _ (TupP ps) = parens $ sep $ punctuate comma $ map ppr ps
pprPat i (ConP s ps) = parensIf (i > noPrec) $ pprName' Applied s
 <+> sep (map (pprPat appPrec) ps)
pprPat i (InfixP p1 n p2)
 = parensIf (i > noPrec) (pprPat opPrec p1 <+>
 pprName' Infix n <+>
 pprPat opPrec p2)
pprPat i (TildeP p) = parensIf (i > noPrec) $ char '~' <> pprPat appPrec p
pprPat i (BangP p) = parensIf (i > noPrec) $ char '!' <> pprPat appPrec p
pprPat i (AsP v p) = parensIf (i > noPrec) $ ppr v <> text "@"
 <> pprPat appPrec p
pprPat _ WildP = text "_"
pprPat _ (RecP nm fs)
 = parens $ ppr nm
 <+> braces (sep $ punctuate comma $
 map (\(s,p) -> ppr s <+> equals <+> ppr p) fs)
pprPat _ (ListP ps) = brackets $ sep $ punctuate comma $ map ppr ps
pprPat i (SigP p t) = parensIf (i > noPrec) $ ppr p <+> text "::" <+> ppr t

------------------------------
instance Ppr Dec where
 ppr = ppr_dec True

ppr_dec :: Bool -- declaration on the toplevel?
 -> Dec 
 -> Doc
ppr_dec _ (FunD f cs) = vcat $ map (\c -> ppr f <+> ppr c) cs
ppr_dec _ (ValD p r ds) = ppr p <+> pprBody True r
 $$ where_clause ds
ppr_dec _ (TySynD t xs rhs) 
 = ppr_tySyn empty t (hsep (map ppr xs)) rhs
ppr_dec _ (DataD ctxt t xs cs decs) 
 = ppr_data empty ctxt t (hsep (map ppr xs)) cs decs
ppr_dec _ (NewtypeD ctxt t xs c decs)
 = ppr_newtype empty ctxt t (sep (map ppr xs)) c decs
ppr_dec _ (ClassD ctxt c xs fds ds) 
 = text "class" <+> pprCxt ctxt <+> ppr c <+> hsep (map ppr xs) <+> ppr fds
 $$ where_clause ds
ppr_dec _ (InstanceD ctxt i ds) = text "instance" <+> pprCxt ctxt <+> ppr i
 $$ where_clause ds
ppr_dec _ (SigD f t) = ppr f <+> text "::" <+> ppr t
ppr_dec _ (ForeignD f) = ppr f
ppr_dec _ (PragmaD p) = ppr p
ppr_dec isTop (FamilyD flav tc tvs k) 
 = ppr flav <+> maybeFamily <+> ppr tc <+> hsep (map ppr tvs) <+> maybeKind
 where
 maybeFamily | isTop = text "family"
 | otherwise = empty

 maybeKind | (Just k') <- k = text "::" <+> ppr k'
 | otherwise = empty
ppr_dec isTop (DataInstD ctxt tc tys cs decs) 
 = ppr_data maybeInst ctxt tc (sep (map pprParendType tys)) cs decs
 where
 maybeInst | isTop = text "instance"
 | otherwise = empty
ppr_dec isTop (NewtypeInstD ctxt tc tys c decs) 
 = ppr_newtype maybeInst ctxt tc (sep (map pprParendType tys)) c decs
 where
 maybeInst | isTop = text "instance"
 | otherwise = empty
ppr_dec isTop (TySynInstD tc tys rhs) 
 = ppr_tySyn maybeInst tc (sep (map pprParendType tys)) rhs
 where
 maybeInst | isTop = text "instance"
 | otherwise = empty

ppr_data :: Doc -> Cxt -> Name -> Doc -> [Con] -> [Name] -> Doc
ppr_data maybeInst ctxt t argsDoc cs decs
 = text "data" <+> maybeInst
 <+> pprCxt ctxt
 <+> ppr t <+> argsDoc
 <+> sep (pref $ map ppr cs)
 $$ if null decs
 then empty
 else nest nestDepth
 $ text "deriving"
 <+> parens (hsep $ punctuate comma $ map ppr decs)
 where 
 pref :: [Doc] -> [Doc]
 pref [] = [] -- No constructors; can't happen in H98
 pref (d:ds) = (char '=' <+> d):map (char '|' <+>) ds

ppr_newtype :: Doc -> Cxt -> Name -> Doc -> Con -> [Name] -> Doc
ppr_newtype maybeInst ctxt t argsDoc c decs
 = text "newtype" <+> maybeInst
 <+> pprCxt ctxt
 <+> ppr t <+> argsDoc
 <+> char '=' <+> ppr c
 $$ if null decs
 then empty
 else nest nestDepth
 $ text "deriving"
 <+> parens (hsep $ punctuate comma $ map ppr decs)

ppr_tySyn :: Doc -> Name -> Doc -> Type -> Doc
ppr_tySyn maybeInst t argsDoc rhs
 = text "type" <+> maybeInst <+> ppr t <+> argsDoc <+> text "=" <+> ppr rhs

------------------------------
instance Ppr FunDep where
 ppr (FunDep xs ys) = hsep (map ppr xs) <+> text "->" <+> hsep (map ppr ys)
 ppr_list [] = empty
 ppr_list xs = char '|' <+> sep (punctuate (text ", ") (map ppr xs))

------------------------------
instance Ppr FamFlavour where
 ppr DataFam = text "data"
 ppr TypeFam = text "type"

------------------------------
instance Ppr Foreign where
 ppr (ImportF callconv safety impent as typ)
 = text "foreign import"
 <+> showtextl callconv
 <+> showtextl safety
 <+> text (show impent)
 <+> ppr as
 <+> text "::" <+> ppr typ
 ppr (ExportF callconv expent as typ)
 = text "foreign export"
 <+> showtextl callconv
 <+> text (show expent)
 <+> ppr as
 <+> text "::" <+> ppr typ

------------------------------
instance Ppr Pragma where
 ppr (InlineP n (InlineSpec inline conlike activation))
 = text "{-#"
 <+> (if inline then text "INLINE" else text "NOINLINE")
 <+> (if conlike then text "CONLIKE" else empty)
 <+> ppr_activation activation 
 <+> ppr n
 <+> text "#-}"
 ppr (SpecialiseP n ty Nothing)
 = sep [ text "{-# SPECIALISE" 
 , ppr n <+> text "::"
 , ppr ty
 , text "#-}"
 ]
 ppr (SpecialiseP n ty (Just (InlineSpec inline _conlike activation)))
 = sep [ text "{-# SPECIALISE" <+> 
 (if inline then text "INLINE" else text "NOINLINE") <+>
 ppr_activation activation
 , ppr n <+> text "::"
 , ppr ty
 , text "#-}"
 ]
 where

ppr_activation :: Maybe (Bool, Int) -> Doc
ppr_activation (Just (beforeFrom, i))
 = brackets $ (if beforeFrom then empty else char '~') <+> int i
ppr_activation Nothing = empty

------------------------------
instance Ppr Clause where
 ppr (Clause ps rhs ds) = hsep (map (pprPat appPrec) ps) <+> pprBody True rhs
 $$ where_clause ds

------------------------------
instance Ppr Con where
 ppr (NormalC c sts) = ppr c <+> sep (map pprStrictType sts)
 ppr (RecC c vsts)
 = ppr c <+> braces (sep (punctuate comma $ map pprVarStrictType vsts))
 ppr (InfixC st1 c st2) = pprStrictType st1
 <+> pprName' Infix c
 <+> pprStrictType st2
 ppr (ForallC ns ctxt con) = text "forall" <+> hsep (map ppr ns)
 <+> char '.' <+> pprCxt ctxt <+> ppr con

------------------------------
pprVarStrictType :: (Name, Strict, Type) -> Doc
-- Slight infelicity: with print non-atomic type with parens
pprVarStrictType (v, str, t) = ppr v <+> text "::" <+> pprStrictType (str, t)

------------------------------
pprStrictType :: (Strict, Type) -> Doc
-- Prints with parens if not already atomic
pprStrictType (IsStrict, t) = char '!' <> pprParendType t
pprStrictType (NotStrict, t) = pprParendType t

------------------------------
pprParendType :: Type -> Doc
pprParendType (VarT v) = ppr v
pprParendType (ConT c) = ppr c
pprParendType (TupleT 0) = text "()"
pprParendType (TupleT n) = parens (hcat (replicate (n-1) comma))
pprParendType ArrowT = parens (text "->")
pprParendType ListT = text "[]"
pprParendType other = parens (ppr other)

instance Ppr Type where
 ppr (ForallT tvars ctxt ty)
 = text "forall" <+> hsep (map ppr tvars) <+> text "."
 <+> pprCxt ctxt <+> ppr ty
 ppr (SigT ty k) = ppr ty <+> text "::" <+> ppr k
 ppr ty = pprTyApp (split ty)

pprTyApp :: (Type, [Type]) -> Doc
pprTyApp (ArrowT, [arg1,arg2]) = sep [pprFunArgType arg1 <+> text "->", ppr arg2]
pprTyApp (ListT, [arg]) = brackets (ppr arg)
pprTyApp (TupleT n, args)
 | length args == n = parens (sep (punctuate comma (map ppr args)))
pprTyApp (fun, args) = pprParendType fun <+> sep (map pprParendType args)

pprFunArgType :: Type -> Doc	-- Should really use a precedence argument
-- Everything except forall and (->) binds more tightly than (->)
pprFunArgType ty@(ForallT {}) = parens (ppr ty)
pprFunArgType ty@((ArrowT `AppT` _) `AppT` _) = parens (ppr ty)
pprFunArgType ty@(SigT _ _) = parens (ppr ty)
pprFunArgType ty = ppr ty

split :: Type -> (Type, [Type]) -- Split into function and args
split t = go t []
 where go (AppT t1 t2) args = go t1 (t2:args)
 go ty args = (ty, args)

------------------------------
instance Ppr TyVarBndr where
 ppr (PlainTV nm) = ppr nm
 ppr (KindedTV nm k) = parens (ppr nm <+> text "::" <+> ppr k)

instance Ppr Kind where
 ppr StarK = char '*'
 ppr (ArrowK k1 k2) = pprArrowArgKind k1 <+> text "->" <+> ppr k2

pprArrowArgKind :: Kind -> Doc
pprArrowArgKind k@(ArrowK _ _) = parens (ppr k)
pprArrowArgKind k = ppr k

------------------------------
pprCxt :: Cxt -> Doc
pprCxt [] = empty
pprCxt [t] = ppr t <+> text "=>"
pprCxt ts = parens (hsep $ punctuate comma $ map ppr ts) <+> text "=>"

------------------------------
instance Ppr Pred where
 ppr (ClassP cla tys) = ppr cla <+> sep (map pprParendType tys)
 ppr (EqualP ty1 ty2) = pprFunArgType ty1 <+> char '~' <+> pprFunArgType ty2

------------------------------
instance Ppr Range where
 ppr = brackets . pprRange
 where pprRange :: Range -> Doc
 pprRange (FromR e) = ppr e <> text ".."
 pprRange (FromThenR e1 e2) = ppr e1 <> text ","
 <> ppr e2 <> text ".."
 pprRange (FromToR e1 e2) = ppr e1 <> text ".." <> ppr e2
 pprRange (FromThenToR e1 e2 e3) = ppr e1 <> text ","
 <> ppr e2 <> text ".."
 <> ppr e3

------------------------------
where_clause :: [Dec] -> Doc
where_clause [] = empty
where_clause ds = nest nestDepth $ text "where" <+> vcat (map (ppr_dec False) ds)

showtextl :: Show a => a -> Doc
showtextl = text . map toLower . show