There's a (somewhat rambling, but interesting) talk on the effort to rewrite the lisp symbolic math system Axiom[a] as a literate program (spanning several books) - precisely in order to make it possible to refactor and maintain the code:

"Literate Programming in the Large": https://m.youtube.com/watch?v=Av0PQDVTP4A

[a] http://axiom-developer.org/