mirror of
https://github.com/idris-lang/Idris2.git
synced 2024-09-11 13:36:08 +03:00
37 lines
1.1 KiB
Idris
37 lines
1.1 KiB
Idris
module InterpE
|
|
|
|
data Expr = Var String -- variables
|
|
| Val Int -- values
|
|
| Add Expr Expr -- addition
|
|
|
|
data Eval : Type -> Type where
|
|
MkEval : (List (String, Int) -> Maybe a) -> Eval a
|
|
|
|
fetch : String -> Eval Int
|
|
fetch x = MkEval (\e => fetchVal e) where
|
|
fetchVal : List (String, Int) -> Maybe Int
|
|
fetchVal [] = Nothing
|
|
fetchVal ((v, val) :: xs) = if (x == v)
|
|
then (Just val)
|
|
else (fetchVal xs)
|
|
|
|
Functor Eval where
|
|
map f (MkEval g) = MkEval (\e => map f (g e))
|
|
|
|
Applicative Eval where
|
|
pure x = MkEval (\e => Just x)
|
|
|
|
(<*>) (MkEval f) (MkEval g) = MkEval (\x => app (f x) (g x)) where
|
|
app : Maybe (a -> b) -> Maybe a -> Maybe b
|
|
app (Just fx) (Just gx) = Just (fx gx)
|
|
app _ _ = Nothing
|
|
|
|
eval : Expr -> Eval Int
|
|
eval (Var x) = fetch x
|
|
eval (Val x) = [| x |]
|
|
eval (Add x y) = [| eval x + eval y |]
|
|
|
|
runEval : List (String, Int) -> Expr -> Maybe Int
|
|
runEval env e = case eval e of
|
|
MkEval envFn => envFn env
|