Grammars and derivations

Hopcroft 2e §5.1–5.2. Type a grammar and a string; the engine finds a leftmost or rightmost derivation and replays it — sentential form, applied production and parse tree in step, with the yield read off the leaves so the tree-derivation correspondence is watched rather than asserted.

Also here: the ambiguity detector, left recursion elimination and, for Module 4, the simplification pipeline and CNF.