文字列を利用した演算（評価過程）
expval (Let ([Decl "n" (Num "10")]) (If (Rexpr LessEq (Var "n") (Num "0"))(Num "1", Bexpr Minus (Var "n") (Num "2")))) none
= expval (If (Rexpr LessEq (Var "n") (Num "0"))(Num "1", Bexpr Minus (Var "n") (Num "2"))) (recdecl ([Decl "n" (Num "10")]) none)
| v = expval (Num "1") (recdecl ([Decl "n" (Num "10")]) none)
| otherwise = expval (Bexpr Minus (Var "n") (Num "2")) (recdecl ([Decl "n" (Num "10")]) none)
where
V_Bool v = expval (Rexpr LessEq (Var "n") (Num "0")) (recdecl ([Decl "n" (Num "10")]) none)
= V_Bool (relopr LessEq v v') =
where
V_Int v = expval (Var "n") (recdecl ([Decl "n" (Num "10")]) none)
= lookup1 (recdecl ([Decl "n" (Num "10")]) none) "n"
= (recdecl ([Decl "n" (Num "10")]) none) "n"
= (foldl declenv' "n" ([Decl "n" (Num "10")]))
declenv' "n" ([Decl "n" (Num "10")]) = declenv ([Decl "n" (Num "10")]) "n" "n"
= update "n" "n" (expval (Num "10")) "n"
= update "n" "n" (V_Int 10)
= V_Int 10
= foldl (V_Int 10)
=V_Int 10
V_Int v' = expval (Num "0") (recdecl ([Decl "n" (Num "10")]) none)
= V_Int (Numval "0")
= V_Int 0
= V_Bool (relopr LessEq 10 0)
= 10(<=)0 = V_Bool False
=expval (Bexpr Minus (Var "n") (Num "2")) (recdecl ([Decl "n" (Num "10")]) none)
=V_Int (binopr Minus v v')
where
V_Int v = expval (Var "n") (recdecl ([Decl "n" (Num "10")]) none)
= lookup1 (recdecl ([Decl "n" (Num "10")]) none) "n"
= (recdecl ([Decl "n" (Num "10")]) none) "n"
=(foldl declenv' "n" ([Decl "n" (Num "10")]))
declenv' "n" ([Decl "n" (Num "10")]) = declenv ([Decl "n" (Num "10")]) "n" "n"
= update "n" "n" (expval (Num "10")) "n"
= update "n" "n" (V_Int 10)
= V_Int 10
= foldl (V_Int 10)
=V_Int 10
V_Int v' = expval (Num "2") (recdecl ([Decl "n" (Num "10")]) none)
= V_Int (numval "2")
= V_Int 2
=V_Int (binopr Minus (10) (2))
=V_Int ((10)(-)(2))
=V_Int 8
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