Bottom-up parsing

In computer science, parsing reveals the grammatical structure of linear input text, as a first step in working out its meaning. Bottom-up parsing identifies and processes the text's lowest-level small details first, before its mid-level structures, and leaving the highest-level overall structure to last.

Bottom-up Versus Top-down

The bottom-up name comes from the concept of a parse tree, in which the most detailed parts are at the bushy bottom of the (upside-down) tree, and larger structures composed from them are in successively higher layers, until at the top or "root" of the tree a single unit describes the entire input stream. A bottom-up parse discovers and processes that tree starting from the bottom left end, and incrementally works its way upwards and rightwards.<ref> Compilers: Principles, Techni