Each tuple contains a string representing its type as the first element, and then other information in the other elements of the tuple. The lexer and parser take some text like this:Īnd break it into parts, and then assemble it into a tree structure like this:Ĭell is written in Python and uses Python tuples to hold all the structures it represents.
Now we are ready to start understanding and evaluating the parts of that tree structure to produce values and behaviour.īy the end of this article you will have seen all the most important parts of a programming language, and be ready to write your own! In part one we broke up the code into chunks like numbers, strings and symbols (lexing), and in part two we assembled those parts into a tree structure (parsing). This is the third part of our series on writing a programming language.
Andy Balaam continues writing a programming language with the evaluator.
We’ve parsed our tokens: now we need turn them into values.
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