Recursive ascent parser information

In computer science, recursive ascent parsing is a technique for implementing an LR parser which uses mutually-recursive functions rather than tables. Thus, the parser is directly encoded in the host language similar to recursive descent. Direct encoding usually yields a parser which is faster than its table-driven equivalent^[1] for the same reason that compilation is faster than interpretation. It is also (nominally) possible to hand edit a recursive ascent parser, whereas a tabular implementation is nigh unreadable to the average human.

Recursive ascent was first described by Thomas Pennello in his article Pennello, Thomas J. (1986). "Very fast LR parsing". Proceedings of the 1986 SIGPLAN symposium on Compiler construction - SIGPLAN '86. pp. 145–151. doi:10.1145/12276.13326. ISBN 0897911970. S2CID 17214407. in 1986. He was not intending to create a hand-editable implementation of an LR parser, but rather a maintainable and efficient parser implemented in assembly language. The technique was later expounded upon by G.H. Roberts^[2] in 1988 as well as in an article by Leermakers, Augusteijn, Kruseman Aretz^[3] in 1992 in the journal Theoretical Computer Science. An extremely readable description of the technique was written by Morell and Middleton^[4] in 2003. A good exposition can also be found in a TOPLAS article by Sperber and Thiemann.^[5]

Recursive ascent has also been merged with recursive descent, yielding a technique known as recursive ascent/descent. This implementation technique is arguably easier to hand-edit due to the reduction in states and fact that some of these states are more intuitively top-down rather than bottom up. It can also yield some minimal performance improvements over conventional recursive ascent.^[6]