Golang GUI Calculator

package mainimport (    "strconv"    "fyne.io/fyne/v2/app"    "fyne.io/fyne/v2/container"    "fyne.io/fyne/v2/widget"    "github.com/Knetic/govaluate")func main() {    myApp := app.New()    myWindow := myApp.NewWindow("Calculator")    mainResult := widget.NewLabel("")    mainS := ""    mainResult.SetText(mainS)    one := widget.NewButton("1", func() {        mainS += "1"    })    two := widget.NewButton("2", func() {        mainS += "2"    })    three := widget.NewButton("3", func() {        mainS += "3"    })    four := widget.NewButton("4", func() {        mainS += "4"    })    five := widget.NewButton("5", func() {        mainS += "5"    })    six := widget.NewButton("6", func() {        mainS += "6"    })    seven := widget.NewButton("7", func() {        mainS += "7"    })    eigth := widget.NewButton("8", func() {        mainS += "8"    })    nine := widget.NewButton("9", func() {        mainS += "9"    })    zero := widget.NewButton("0", func() {        mainS += "0"    })    clear := widget.NewButton("C", func() {        mainS = ""    })    plus := widget.NewButton("+", func() {        mainS += "+"    })    minus := widget.NewButton("-", func() {        mainS += "-"    })    multiply := widget.NewButton("*", func() {        mainS += "*"    })    divide := widget.NewButton("/", func() {        mainS += "/"    })    #fourth    equal := widget.NewButton("=", func() {        expression, err := govaluate.NewEvaluableExpression(mainS)        if err == nil {            result, err := expression.Evaluate(nil)            if err == nil {                mainS = strconv.FormatFloat(result.(float64), 'f', -1, 64)            } else {                mainS = err.Error()            }        } else {            mainS = err.Error()        }    })    #five updating it each time    go func() {        for {            mainResult.SetText(mainS)        }    }()    #creating layout from the given buttons    myWindow.SetContent(container.NewVBox(        mainResult,        container.NewGridWithColumns(3,            divide,            multiply,            minus,            // plus,        ),        container.NewGridWithColumns(2,            container.NewGridWithRows(3,                container.NewGridWithColumns(3,                    seven,                    eigth,                    nine,                ),                container.NewGridWithColumns(3,                    four,                    five,                    six,                ),                container.NewGridWithColumns(3,                    one,                    two,                    three,                ),            ),            plus,        ),        container.NewGridWithColumns(2,            container.NewGridWithColumns(2,                clear,                zero,            ),            equal,        ),    ),    )    myWindow.ShowAndRun()}