gopl-zh.github.com/vendor/gopl.io/ch7/eval/ast.go

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