module E.Eval(eval, strong) where

-- Simple lambda Calculus interpreter
-- does not handle recursive Let or Case statements, but those don't appear in types anyway.

import Control.Monad.Writer
import qualified Data.Map as Map

import Doc.PPrint
import E.E
import E.FreeVars
import {-# SOURCE #-} E.Show
import E.Subst



eval :: E -> E
eval term = eval' term []  where
    -- final terms
    eval' t@EVar {} [] = t
    eval' (ELam v body) [] = check_eta $ ELam v (eval body)
    eval' (EPi v body) [] = check_eta $ EPi v (eval body)
    eval' e@Unknown [] = e
    eval' e@ESort {} [] = e
    eval' (ELit lc@LitCons { litArgs = es }) [] = ELit lc { litArgs = map eval es }
    eval' e@ELit {} [] = e

    -- argument applications
    eval' (ELit lc@LitCons { litArgs = es, litType = EPi tb tt }) (t:rest) = eval' (ELit lc { litArgs = es ++ [t], litType = subst tb t tt }) rest
    eval' (ELit LitCons { litArgs = es, litAliasFor = Just af }) (t:rest) = eval' af (es ++ t:rest)

    eval' (ELam v body) (t:rest) = eval' (subst v t body) rest
    eval' (EPi v body) (t:rest) = eval' (subst v t body) rest   -- fudge
    eval' (EAp t1 t2) stack = eval' t1 (t2:stack)
    eval' t@EVar {} stack = unwind t stack
    eval' ELetRec { eDefs = ds, eBody = e } stack = eval' (f (decomposeDs ds) e) stack where
        f [] e = e
        f (Left (x,y):ds) e =  subst x y (f ds e)
        f (Right _:_) _ = error $ "cannot eval recursive let"
    eval' e@(ELit LitCons {}) stack = unwind e stack
    eval' e _ = error $ "Cannot eval: " ++ show e

    unwind t [] = t
    unwind t (t1:rest) = unwind (EAp t $ eval t1) rest

    -- currently we do not do eta check. etas should only appear for good reason.
    check_eta x = x



{- Lemmih 08.11.26:
'dsMap' is the current scope with known bindings.
Inline all lets and perform beta reduction.
Invariants:
  All variables must be unique. No shadowing is allowed.
  All variables must be named.
-}
strong :: Monad m => [(TVr,E)] -> E -> m E
strong dsMap' term = eval' dsMap term [] where
    dsMap = Map.fromList dsMap'
    --eval' ds t@EVar {} [] = t
    etvr ds tvr = do
        t' <- (eval' ds (tvrType tvr) [])
        return $ tvr { tvrType = t' }
    eval' :: Monad m => Map.Map TVr E -> E -> [E] -> m E

    eval' ds (ELam v body) [] = do
        let ds' = Map.delete v ds
        v' <- etvr ds' v
        body' <- (eval' ds' body [])
        check_eta $ ELam v' body'
    eval' ds (EPi v body) [] = do
        let ds' = Map.delete v ds
        body' <- (eval' ds' body [])
        v' <- etvr ds' v
        check_eta $ EPi v' body'
    eval' ds e@Unknown [] = return e
    eval' ds e@ESort {} [] = return e
    eval' ds (ELit lc@LitCons { litArgs = es, litType = t }) [] = do
        es' <- mapM (\e -> eval' ds e []) es
        t' <-  (eval' ds t [])
        return $ ELit $ lc { litArgs = es', litType = t' }
    eval' ds e@ELit {} [] = return e
    eval' ds (ELit lc@LitCons { litArgs = es, litType = EPi tb tt }) (t:rest) = eval' ds (ELit lc { litArgs = es ++ [t], litType = subst tb t tt }) rest
    eval' ds (ELit LitCons { litArgs = es, litAliasFor = Just af }) (t:rest) = eval' ds af (es ++ t:rest)
    eval' ds (ELam v body) (t:rest) = eval' ds (subst v t body) rest
    eval' ds (EPi v body) (t:rest) = eval' ds (subst v t body) rest   -- fudge
    eval' ds (EAp t1 t2) stack = eval' ds t1 (t2:stack)
    eval' _ds (EVar TVr { tvrIdent = 0 }) _stack = fail "empty ident in term"
    eval' ds t@(EVar v) stack
        | Just x <- Map.lookup v ds = eval' ds x stack
        | otherwise = do
            tvr <- etvr ds v
            unwind ds (EVar tvr) stack
    eval' ds ELetRec { eDefs = ds', eBody = e } stack = eval' (Map.fromList ds'  `mappend` ds) e  stack
    eval' ds e@(ELit LitCons {}) stack = unwind ds e stack
    eval' ds (EError s ty) (t:rest) = do
        nt <- eval' ds (EAp ty t) rest
        return (EError s nt)
    eval' ds e@EError {} [] = do return e

    eval' ds e stack= fail $ "Cannot strong: \n" ++ render (pprint (e,stack))

    unwind ds t [] = return t
    unwind ds t (t1:rest) = do
        e <-  eval' ds t1 []
        unwind ds (EAp t $ e) rest

    -- currently we do not do eta check. etas should only appear for good reason.
    check_eta x = return x