Neat. If you add some automatic memoization, I'll use it for my next project!

Here's the use case:

expr := ...

rule1 := expr foo expr

rule2 := expr bar

When trying to match rule1 and failing, it is great to have the expr part of it already parsed and ready for trying out rule2.

This doesn't have to be done extremely well (see PEG/Packrat parsing for that) but even a little bit, maybe one term or something like that helps a lot.