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40 lines
1.1 KiB
Python
40 lines
1.1 KiB
Python
LitExpr = Class {.i = Int}, Impl := Show
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LitExpr.
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new i = Self::__new__ {.i;}
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show &self = "{self.i}"
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AddExpr = Class {.lhs = Expr, .rhs = Expr}, Impl := Show
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AddExpr.
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new lhs, rhs = Self::__new__ {.lhs; .rhs}
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show &self = "{self.lhs} + {self.rhs}"
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SubExpr = Class {.lhs = Expr, .rhs = Expr}, Impl := Show
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SubExpr.
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new lhs, rhs = Self::__new__ {.lhs; .rhs}
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show &self = "{self.lhs} - {self.rhs}"
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PosExpr = Class {.expr = Expr}, Impl := Show
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PosExpr.
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new expr = Self::__new__ {.expr;}
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show &self = "+{self.expr}"
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NegExpr = Class {.expr = Expr}, Impl := Show
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NegExpr.
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new expr = Self::__new__ {.expr;}
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show &self = "-{self.expr}"
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Expr = Enum:
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LitExpr
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AddExpr
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SubExpr
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NegExpr
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Expr.
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lit = Self.cons(LitExpr)
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add = Self.cons(AddExpr)
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eval self =
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match self:
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l: Expr.LitExpr -> l.i
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a: Expr.AddExpr -> a.lhs + a.rhs
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s: Expr.SubExpr -> s.lhs - s.rhs
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p: Expr.PosExpr -> p.expr
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n: Expr.NegExpr -> -n.expr
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expr = Expr.add Expr.lit(1), Expr.lit(2)
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print! expr # 1 + 2
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assert expr.eval() == 3
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