Most of the function of this interpreter is derived from the NIST G-code standard. The data returned by the parseFile callback is a list of G-code blocks, where each block is an object with a num property (the G-code line number) and a words property (the list of G-code words in that block) Each G-code word is a list of two items, the word letter (G, M, X,Y,Z, etc.) and the word argument. Word arguments are typically numbers, but the parser supports full expressions, including parameter values, so in the event that an expression or parameter value is provided, an expression-tree-like object is returned that must be evaluated. Currently, this is left as an exercise for the reader.