I would argue that sentence diagramming is of dubious use outside of an ESL or primary school class. And even then the English language is such a self-contradicting mongrel tongue that it's effectively rule-less.

It's a living, evolving, consensus language. It can't be nailed down to an algorithm. It's a language in which writers who break the rules become legendary. Would James Joyce or Charles Dodgson or the Bard himself have diagrammed a sentence? Heck no. They played with grammar and spelling the way a child plays with a pile of lego: with enthusiasm and imagination and a gleeful disregard for the instructions.