eval

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v0.0.0-...-94c99f4 Latest Latest Go to latest Published: Dec 23, 2019 License: Apache-2.0 Imports: 6 Imported by: 0

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github.com/bbc/eng-golang-workshop

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Documentation ¶

Overview ¶

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

Package eval provides an expression evaluator.

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

Index ¶

func Format(e Expr) string
type Env
type Expr
- func Parse(input string) (_ Expr, err error)
type Var

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
	// Pretty-print the syntax tree
	String() string
	// Brace() reports if this Expr has an enclosing brace
	Brace() bool
}

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) Brace ¶

func (v Var) Brace() bool

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

Source Files ¶

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