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DadgadCafe/lambda-viewer.hs

Created June 3, 2017 12:36
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lambda-viewer.hs
-- lambda
data Term = Lam Var Term
| Var Var
| App Term Term -- func application
data Var = V String
instance Show Var where
show (V s) = s
instance Show Term where
show (Var v) = show v
show (Lam v t) = "λ" ++ show v ++ "." ++ show t
show (App t1 t2) = "(" ++ show t1 ++ " " ++ show t2 ++ ")"
-- exercises
-- a b c d e f
(App (App (App (App (App (Var (V "a"))
(Var (V "b")))
(Var (V "c")))
(Var (V "d")))
(Var (V "e")))
(Var (V "f")))
-- (g h) (i j)
(App (App (Var (V "g"))
(Var (V "h")))
(App (Var (V "i"))
(Var (V "j"))))
-- λx.f (λy.f y)
(Lam (V "x")
(App (f)
(Lam (y)
(App (f)
(Var (y)))))
where f = Var (V "f")
y = V "y"
-- (λf.f x y) (λx.λy.x)
(App (Lam (f)
(App (App (Val f)
(Val (V "x")))
(Val (V "y"))))
(Lam (x)
(Lam (V "y")
(Val x))))
where f = V "f"
x = V "x"
-- f g λx.y z
(App (App (App (Val (V "f"))
(Val (V "g")))
(Lam (V "x")
(Val (V "y"))))
(Val (V "z")))
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