Evaluate arithmetic expressions in Go

eval.go

package main

import (
	"errors"
	"go/constant"
	"go/token"
	"go/types"
	"log"
)

func Eval(expr string) (int64, error) {
	fs := token.NewFileSet()
	tv, err := types.Eval(fs, nil, token.NoPos, expr)
	if err != nil {
		return 0, err
	}
	if tv.Value.Kind() != constant.Int {
		return 0, errors.New("expression does not evaluate to an integer")
	}
	x, exact := constant.Int64Val(tv.Value)
	if !exact {
		return 0, errors.New("inexact result")
	}
	return x, nil
}

func main() {
	exprs := []string{
		"1",
		"1<<32",
		"3-2",
		"true",
		"1<<100",
		"sdfsdfsdf<1222asdfsdf",
	}
	for _, expr := range exprs {
		x, err := Eval(expr)
		log.Printf("expr=%q x=%d err=%v", expr, x, err)
	}
}

https://play.golang.org/p/nmsmWCkwaYq