Evaluate formula in Go

Question

Using Go (golang) I\'d like to take a string with a formula and evaluate it with pre-defined values. Here\'s a way to do it with python\'s parser module:

<

Answer 1

Googling around I found this: https://github.com/sbinet/go-eval

It appears to be an eval loop for Go.

go get github.com/sbinet/go-eval/cmd/go-eval
go install github.com/sbinet/go-eval/cmd/go-eval
go-eval

Answer 2

I have made my own equation evaluator, using Djikstra's Shunting Yard Algorithm. It supports all operators, nested parenthesis, functions and even user defined variables.

It is written in pure go

https://github.com/marcmak/calc

Answer 3

With this code you can evaluate dynamically any formula and return true or false:

package main

import (
    "go/token"
    "go/types"
)

func main() {
    fs := token.NewFileSet()
    tv, err := types.Eval(fs, nil, token.NoPos, "(1 + 4) >= 5")
    if err != nil {
        panic(err)
    }
    println(tv.Value.String())
}

Answer 4

This package will probably work for your needs: https://github.com/Knetic/govaluate

expression, err := govaluate.NewEvaluableExpression("(x + 2) / 10");

parameters := make(map[string]interface{}, 8)
parameters["x"] = 8;

result, err := expression.Evaluate(parameters);

Answer 5

You will probably need to resort to a library that interprets math statements or have to write your own parser. Python being a dynamic language can parse and execute python code at runtime. Standard Go cannot do that.

If you want to write a parser on your own, the go package will be of help. Example (On play):

import (
    "go/ast"
    "go/parser"
    "go/token"
)

func main() {
    fs := token.NewFileSet()
    tr, _ := parser.ParseExpr("(3-1) * 5")
    ast.Print(fs, tr)
}

The resulting AST (Abstract Syntax Tree) can then be traversed and interpreted as you choose (handling '+' tokens as addition for the now stored values, for example).

Answer 6

There's nothing built in that could do that (remember, Go is not a dynamic language).

However, you can always use bufio.Scanner and build your own parser.