module HW4Part1 where

data Reg = A | B | R

data Expr
    = Lit Int
    | Reg Reg
    | Plus Expr Expr
    | Leq Expr Expr
    | Not Expr

type Prog = [Stmt]

data Stmt
    = Store Reg Expr
    | If Expr Prog Prog
    | Loop Prog
    | Break

program :: Prog
program =
    [ Store A $ Lit 7
    , Store B $ Lit 9
    , Store R $ Lit 0
    , Loop $
        [ If (Reg A `Leq` Lit 0)
            [ Break ]
            [ Store R $ Reg R `Plus` Reg B
            , Store A $ Reg A `Plus` Lit (-1)
            ]
        ]
    ]

while :: Expr -> Prog -> Stmt
while cond body = Loop [ If cond body [ Break ] ]

sumFromTo :: Int -> Int -> Prog
sumFromTo f t =
    [ Store A $ Lit f
    , Store B $ Lit t
    , Store R $ Lit 0
    , while (Leq (Reg A) (Reg B))
        [ Store R $ Reg R `Plus` Reg A
        , Store A $ Reg A `Plus` (Lit 1)
        ]
    ]