eval

package
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Published: Jun 28, 2018 License: MIT Imports: 6 Imported by: 0

README

Exercise 7.13 (P205)

Add a String method to Expr to pretty-print the syntax tree. Check that the results, when parsed again, yield an equivalent tree.

Documentation

Overview

Package eval provides an expression evaluator.

Index

Constants

This section is empty.

Variables

This section is empty.

Functions

func Format

func Format(e Expr) string

Format formats an expression as a string. It does not attempt to remove unnecessary parens.

Types

type Env

type Env map[Var]float64

type Expr

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
	// String returns a human readable string of the Expr
	String() string
}

An Expr is an arithmetic expression.

func Parse

func Parse(input string) (_ Expr, err error)

Parse parses the input string as an arithmetic expression.

expr = num                         a literal number, e.g., 3.14159
     | id                          a variable name, e.g., x
     | id '(' expr ',' ... ')'     a function call
     | '-' expr                    a unary operator (+-)
     | expr '+' expr               a binary operator (+-*/)

type Var

type Var string

A Var identifies a variable, e.g., x.

func (Var) Check

func (v Var) Check(vars map[Var]bool) error

func (Var) Eval

func (v Var) Eval(env Env) float64

func (Var) String

func (v Var) String() string

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