How and why I designed my own approximated implementations
cos. The approximation error is quite
small, and the functions are fast and vectorizable. For example, my
logapprox function is 7.5x faster in tight loops than
function, while being more precise.
Contrary to top-down (LL) parsers, which do not support left recursion, bottom-up (LR) parsers support both left recursion and right recursion. When defining a list-like construct, a user of an LR parser generator, such as Menhir, faces a choice between these two flavors. Which one should she prefer?
Two considerations guide this choice: expressiveness (which flavor leads to fewer conflicts?) and performance (which flavor leads to a more efficient parser?).
In this post, I am mainly interested in discussing expressiveness. I also comment on performance in the setting of Menhir.
As we will see, the bottom line is that neither formulation seems deeply preferable to the other.