Is it possible to read user input in Lua as a math operation?

user_17211857 0
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I'm trying to write something that takes input in the form of a function, such as "f(x) = 2*x + 5", and have it be calculated as a normal equation.

What I currently have is:

print("give any function") --vague as placeholder
x=50
str=string.gsub(io.read(), "x", tostring(x))
print(str*1)

It works fine when you have the x variable in the input, replacing it with the previously set x variable as before. What happens is when you put something in such as "1+1", it doesn't accept it.

Is there a way to get input from something such as "1+1" to be calculable to 2, rather than just the string it is given as?

What I am essentially asking here: Any user input under the format "number operator number" only reads as a string, not a calculable equation. Any workaround?

math lua
1 Answers

You can use some more detailed gsub and then load the function as lua code. As the format of 1 + 1 is not really a "function" format we will need to add some extra handling for the case when the function is just an operation

function evaluateFunction(funcStr, x)
  
  funcStr = "return " .. funcStr
  funcStr, replaced = funcStr:gsub("f%(", "function(")
  funcStr = funcStr:gsub("=", "return")
  
  if replaced ~= 0 then
    funcStr = funcStr .. " end"
  end
  
  print(funcStr)

  local func = load(funcStr)()
  if type(func) == "function" then
    print(func(x))    
  else
    print(func)
  end
end

evaluateFunction("f(x) = 2*x + 5", 50)
evaluateFunction("f() = 2*5")
evaluateFunction("1 + 1")

Output:

return function(x) return 2*x + 5 end

105

return function() return 2*5 end

10

return 1 + 1

2

user_73961480
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