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@Lysxia Lysxia/E.hs
Last active Sep 18, 2019

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type Lets = Exp -> Exp
-- "Stack of lets", functions of this form:
-- (Let b1 . Let b2 . ... . Let bn)
snoc :: Lets -> (Var, Exp) -> Lets
snoc k b = k . Let b
type M = State (T.Text, Int, Lets)
push :: (Var, Exp) -> M Exp
push b = modify' (\(s, c, k) -> (s, c, k `snoc` b))
wrapWithLet :: Exp -> M Exp
wrapWithLet exp = do
(s, c, k) <- get
let var = makeVar s c
put (s, c+1, k `snoc` (var, exp))
return $ Id var
flatten :: Exp -> M Exp
flatten (Sum e1 e2) = do
exp1 <- flatten e1
exp2 <- flatten e2
wrapWithLet $ Sum exp1 exp2
flatten (Neg e) = do
exp <- flatten e
wrapWithLet $ Neg exp
flatten (Let (v, b) body) = do
eBind <- flatten b
push (v, eBind)
flatten body
flatten e = return e
run :: Text -> M Exp -> Exp
run s r = let (i, (_, _, k)) = runState r (s, 0, id) in k i
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