Exercise 33: Parsers

Imagine you're given a huge list of numbers and you have to enter them into a spreadsheet. At first, this huge list is just a raw stream of digits separated by spaces. Your brain automatically breaks the stream of digits at the spaces and creates numbers. That's your brain acting like a scanner. You then take each number, and enter them into rows and columns that have meaning. Your brain is acting like a parser by taking the flat stream of numbers (tokens), and turning them into a 2-dimensional grid of more meaningful rows and columns. The rules you follow for what numbers go into what rows and what columns is your "grammar," and a parser's job is to enforce the grammar just like you would with a spreadsheet.

Let's look at the example Puny Python code from Exercise 32 one more time and discuss parsers from three different viewing angles: