module Ident where

import Operations
-- import Monad

data Ident = 
   IC String            -- raw identifier after parsing, resolved in Rename
 | IW                   -- wildcard

-- below this line: internal representation never returned by the parser
 | IV (Int,String)      -- variable
 | IA (String,Int)      -- argument of cat at position
 | IAV (String,Int,Int) -- argument of cat with bindings at position

  deriving (Eq, Ord, Show, Read)

prIdent :: Ident -> String
prIdent i = case i of
  IC s -> s
  IV (n,s) -> s ++ "_" ++ show n
  IA (s,j) -> s ++ "_" ++ show j
  IAV (s,b,j) -> s ++ "_" ++ show b ++ "_" ++ show j
  IW -> "_"

(identC, identV, identA, identAV, identW) = 
    (IC,     IV,     IA,     IAV,     IW)

-- normal identifier
-- ident s = IC s

-- to mark argument variables
argIdent 0 (IC c) i = identA  (c,i)
argIdent b (IC c) i = identAV (c,b,i)

-- used in lin defaults
strVar = identA ("str",0)

-- wild card
wildIdent = identW

isWildIdent :: Ident -> Bool
isWildIdent = (== wildIdent)

newIdent = identC "#h"

mkIdent :: String -> Int -> Ident
mkIdent s i = identV (i,s)

varIndex :: Ident -> Int
varIndex (IV (n,_)) = n
varIndex _ = -1 --- other than IV should not count

-- refreshing identifiers

type IdState = ([(Ident,Ident)],Int) 

initIdStateN :: Int -> IdState
initIdStateN i = ([],i)

initIdState :: IdState
initIdState = initIdStateN 0

lookVar :: Ident -> STM IdState Ident
lookVar a@(IA _) = return a
lookVar x = do
  (sys,_) <- readSTM
  stm (\s -> maybe (Bad ("cannot find" +++ show x +++ prParenth (show sys))) 
                   return $ 
             lookup x sys >>= (\y -> return (y,s)))

refVar :: Ident -> STM IdState Ident
----refVar IW = return IW --- no update of wildcard
refVar x = do
  (_,m) <- readSTM
  let x' = IV (m, prIdent x)
  updateSTM (\ (sys,mx) -> ((x, x'):sys, mx + 1))
  return x'

refVarPlus :: Ident -> STM IdState Ident
----refVarPlus IW = refVar (identC "h")
refVarPlus x = refVar x


{-
------------------------------
-- to test

refreshExp :: Exp -> Err Exp
refreshExp e = err Bad (return . fst) (appSTM (refresh e) initState)

refresh :: Exp -> STM State Exp
refresh e = case e of
  Atom x  -> lookVar x >>= return . Atom
  App f a -> liftM2 App (refresh f) (refresh a)
  Abs x b -> liftM2 Abs (refVar x)  (refresh b)
  Fun xs a b -> do
    a'  <- refresh a
    xs' <- mapM refVar xs
    b'  <- refresh b
    return $ Fun xs' a' b'

data Exp =
   Atom Ident
 | App Exp Exp
 | Abs Ident Exp
 | Fun [Ident] Exp Exp
  deriving Show

exp1 = Abs (IC "y") (Atom (IC "y"))
exp2 = Abs (IC "y") (App (Atom (IC "y")) (Atom (IC "y")))
exp3 = Abs (IC "y") (Abs (IC "z") (App (Atom (IC "y")) (Atom (IC "z"))))
exp4 = Abs (IC "y") (Abs (IC "y") (App (Atom (IC "y")) (Atom (IC "z"))))
exp5 = Abs (IC "y") (Abs (IC "y") (App (Atom (IC "y")) (Atom (IC "y"))))
exp6 = Abs (IC "y") (Fun [IC "x", IC "y"] (Atom (IC "y")) (Atom (IC "y")))
exp7 = Abs (IL "8") (Atom (IC "y"))

-}