Lua How would I go about writing an Interpreter in Lua?

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Hi, I'm attempting to write an interpreter in Lua, and the first idea was to make it able to run a simple  print function. If anyone is able to answer what's wrong, i would appreciate it.

Here is my main code:

nm = require "numbers"
exec = false

function readAll(file)
    local f = assert(io.open(file, "rb"))
    local content = f:read("*all")
    f:close()
    return content
end

fc = readAll("main.i")

for i=1,#fc,1 do
    if string.find(fc,"prt") and not exec then
        fcs = nm.Trim(fc)
        print(nm.Replace(fcs, 'prt', "_"))
        exec = true
    end
end

Note: numbers Is a module which i created.

Output: prt"hiworld!"

What i was expecting was for the output to be "hiworld", "hi world" or even "_hi world"