Recursive ascent-descent parsers

Abstract

Non-backtracking recursive descent parsers are easy to create but suffer from the disadvantage that they are limited to the relatively small LL(k) class of grammars. Recursive ascent parsers can be built for the much larger LR(k) class of grammars, but they are likely be too large to be useful and manual insertion of semantic action code into the parsers would require considerable skill. A composite approach, dubbed ‘recursive ascent-descent parsing’ or XLC(l) parsing, and which is related to left-corner parsing, solves all the problems. The parser has two parts - a top-down part and a bottom-up part. Either or both parts may be implemented as a collection of recursive functions or by a table-driven parsing algorithm. When a table-driven implementation of the bottom-up part is used, any syntax error recovery scheme applicable to LR parsers can be employed. Small, fast, implementations of the parsers are possible.