A Simple Math Expression Evaluator

A simple math expression evaluator written in Go using Shunting Yard and Reverse Polish.

To install:

go get github.com/darenliang/gomatheval

Examples:

Evaluating expressions

package main

import (
	"fmt"
	"github.com/darenliang/gomatheval"
	"math"
)

func main() {
	fmt.Println(gomatheval.EvalExpression(fmt.Sprintf("-(3+(sin(%v/2))^2)/4", math.Pi)))
	// outputs 1
}

Command-Line Application

package main

import (
	"flag"
	"fmt"
	"github.com/darenliang/gomatheval"
)

func main() {
	optionPtr := flag.String("op", "e", "Select processing option.\n" +
		"e: Evaluate expression\n" +
		"p: Process to Reverse Polish Notation\n" +
		"t: Tokenize expression\n")
	expressionPtr := flag.String("exp", "", "Expression string to be processed")
	flag.Parse()
	switch *optionPtr {
	case "t":
		fmt.Println(gomatheval.SanitizeExpression(*expressionPtr))
	case "p":
		fmt.Println(gomatheval.ParseRPN(gomatheval.SanitizeExpression(*expressionPtr)))
	default:
		fmt.Println(gomatheval.EvalExpression(*expressionPtr))
	}
}

What it supports:

Basic operators such as + (addition), - (subtraction), * (multiplication), / (division), % (modulo), ^ (power).
64-bit floating point operations.
Basic functions such as sin (sine), cos (cosine), tan (tangent), ln (natural logarithm), lg (base 2 logarithm), log (logarithm with variable base). More operators coming soon...
Unary operators for positive and negative numbers. Includes proper handling of unary precedence operations.

How it works:

Every expression is composed of three kinds of tokens:

Operands
Operators/Functions
Parentheses

By tokenizing an expression, we can get the individual elements that make up the expression:

    -(3+(sin(3.141592653589793/2))^2)/4
=>  - ( 3 + ( sin ( 3.141592653589793 / 2 ) ) ^ 2 ) / 4

The tokenized expression is then sanitized and unary operators are converted to unique operators.

    - ( 3 + ( sin ( 3.141592653589793 / 2 ) ) ^ 2 ) / 4
=>  -u ( 3 + ( sin ( 3.141592653589793 / 2 ) ) ^ 2 ) / 4

By using the Shunting Yard Algorithm we can convert this infix notation into postfix notation (also known as Reverse Polish notation).

    -u ( 3 + ( sin ( 3.141592653589793 / 2 ) ) ^ 2 ) / 4
=>  3 3.141592653589793 2 / sin 2 ^ + -u 4 /

By evaluating the postfix notation tokens, we can obtain a final value.

    3 3.141592653589793 2 / sin 2 ^ + -u 4 /
=>  -1