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41 lines
940 B
Go
41 lines
940 B
Go
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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package eval
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// An Expr is an arithmetic expression.
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type Expr interface {
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// Eval returns the value of this Expr in the environment env.
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Eval(env Env) float64
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// Check reports errors in this Expr and adds its Vars to the set.
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Check(vars map[Var]bool) error
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}
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//!+ast
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// A Var identifies a variable, e.g., x.
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type Var string
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// A literal is a numeric constant, e.g., 3.141.
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type literal float64
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// A unary represents a unary operator expression, e.g., -x.
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type unary struct {
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op rune // one of '+', '-'
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x Expr
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}
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// A binary represents a binary operator expression, e.g., x+y.
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type binary struct {
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op rune // one of '+', '-', '*', '/'
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x, y Expr
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}
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// A call represents a function call expression, e.g., sin(x).
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type call struct {
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fn string // one of "pow", "sin", "sqrt"
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args []Expr
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}
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//!-ast
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