44 lines
1.3 KiB
Text
44 lines
1.3 KiB
Text
data Exp where
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EVar : Char -> Exp
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EAbs : Char -> Exp -> Exp
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EApp : Exp -> Exp -> Exp
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EInt : Int -> Exp
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EAdd : Exp -> Exp -> Exp
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data Val where
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VInt : Int -> Val
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VClosure : List (Pair Char Val) -> Char -> Exp -> Val
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lookup : Char -> List (Pair Char Val) -> Val
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lookup x cxt = case cxt of
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Cons p ps => case p of
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Pair y v => case (asciiCode x) == (asciiCode y) of
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True => v
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False => lookup x ps
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insert : Char -> Val -> List (Pair Char Val) -> List (Pair Char Val)
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insert x v cxt = Cons (Pair x v) cxt
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eval : List (Pair Char Val) -> Exp -> Val
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eval cxt exp = case exp of
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EVar x => case lookup x cxt of
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VInt i => VInt i
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VClosure delta x e => eval delta e
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EAbs x e => VClosure cxt x e
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EApp e1 e2 => case eval cxt e1 of
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VClosure delta x f =>
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let v = VClosure cxt x e2 in
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eval (insert x v delta) f
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EInt i => VInt i
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EAdd e1 e2 =>
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let i1 = case eval cxt e1 of { VInt i => i } in
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let i2 = case eval cxt e2 of { VInt i => i } in
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VInt (i1 + i2)
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exp = EApp (EAbs 'x' (EVar 'x')) (EApp (EAbs 'x' (EAdd (EVar 'x') (EInt 100))) (EInt 200))
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-- (λ x . x) (λ x . x + 100) 200
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main : Int
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main = case eval Nil exp of
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VInt i => i
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