Another method is to use a dictionary storing functions:
--Translate string into mathematical expression
local prefixesFunctions = {
["/"] = function (number1,number2)
return number1/number2
end;
["-"] = function (number1,number2)
return number1 - number2
end;
["*"] = function (number1,number2)
return number1*number2
end;
["+"] = function (number1,number2)
return number1+number2
end;
}
From this other post, with a similar gui calculator project: