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operator.go
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operator.go
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// Copyright ©2016-2022 by Richard A. Wilkes. All rights reserved.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, version 2.0. If a copy of the MPL was not distributed with
// this file, You can obtain one at http://mozilla.org/MPL/2.0/.
//
// This Source Code Form is "Incompatible With Secondary Licenses", as
// defined by the Mozilla Public License, version 2.0.
package eval
import (
"unicode"
"unicode/utf8"
)
// OpFunc provides a signature for an Operator's Evaluate function.
type OpFunc func(left, right any) (any, error)
// UnaryOpFunc provides a signature for an Operator's EvaluateUnary function.
type UnaryOpFunc func(arg any) (any, error)
// Operator provides an operator implementation for the Evaluator.
type Operator struct {
Symbol string
Precedence int
Evaluate OpFunc
EvaluateUnary UnaryOpFunc
}
func (o *Operator) match(expression string, start, max int) bool {
if max-start < len(o.Symbol) {
return false
}
matches := o.Symbol == expression[start:start+len(o.Symbol)]
// Hack to allow negative exponents on floating point numbers (i.e. 1.2e-2)
if matches && len(o.Symbol) == 1 && o.Symbol == "-" && start > 1 && expression[start-1:start] == "e" {
ch, _ := utf8.DecodeRuneInString(expression[start-2 : start-1])
if unicode.IsDigit(ch) {
return false
}
}
return matches
}
// OpenParen (
func OpenParen() *Operator {
return &Operator{Symbol: "("}
}
// CloseParen )
func CloseParen() *Operator {
return &Operator{Symbol: ")"}
}
// Not !
func Not(f UnaryOpFunc) *Operator {
return &Operator{
Symbol: "!",
EvaluateUnary: f,
}
}
// LogicalOr ||
func LogicalOr(f OpFunc) *Operator {
return &Operator{
Symbol: "||",
Precedence: 10,
Evaluate: f,
}
}
// LogicalAnd &&
func LogicalAnd(f OpFunc) *Operator {
return &Operator{
Symbol: "&&",
Precedence: 20,
Evaluate: f,
}
}
// Equal ==
func Equal(f OpFunc) *Operator {
return &Operator{
Symbol: "==",
Precedence: 30,
Evaluate: f,
}
}
// NotEqual !=
func NotEqual(f OpFunc) *Operator {
return &Operator{
Symbol: "!=",
Precedence: 30,
Evaluate: f,
}
}
// GreaterThan >
func GreaterThan(f OpFunc) *Operator {
return &Operator{
Symbol: ">",
Precedence: 40,
Evaluate: f,
}
}
// GreaterThanOrEqual >=
func GreaterThanOrEqual(f OpFunc) *Operator {
return &Operator{
Symbol: ">=",
Precedence: 40,
Evaluate: f,
}
}
// LessThan <
func LessThan(f OpFunc) *Operator {
return &Operator{
Symbol: "<",
Precedence: 40,
Evaluate: f,
}
}
// LessThanOrEqual <=
func LessThanOrEqual(f OpFunc) *Operator {
return &Operator{
Symbol: "<=",
Precedence: 40,
Evaluate: f,
}
}
// Add +
func Add(f OpFunc, unary UnaryOpFunc) *Operator {
return &Operator{
Symbol: "+",
Precedence: 50,
Evaluate: f,
EvaluateUnary: unary,
}
}
// Subtract -
func Subtract(f OpFunc, unary UnaryOpFunc) *Operator {
return &Operator{
Symbol: "-",
Precedence: 50,
Evaluate: f,
EvaluateUnary: unary,
}
}
// Multiply *
func Multiply(f OpFunc) *Operator {
return &Operator{
Symbol: "*",
Precedence: 60,
Evaluate: f,
}
}
// Divide /
func Divide(f OpFunc) *Operator {
return &Operator{
Symbol: "/",
Precedence: 60,
Evaluate: f,
}
}
// Modulo %
func Modulo(f OpFunc) *Operator {
return &Operator{
Symbol: "%",
Precedence: 60,
Evaluate: f,
}
}
// Power ^
func Power(f OpFunc) *Operator {
return &Operator{
Symbol: "^",
Precedence: 70,
Evaluate: f,
}
}