Editing Parsing expression grammar (section)

=== Bottom-up PEG parsing ===

A pika parser<ref name="Hut20">{{cite arXiv
| first= Luke A. D. |last=Hutchison
| title = Pika parsing: parsing in reverse solves the left recursion and error recovery problems
| year = 2020
|class=cs.PL
| eprint = 2005.06444
}}</ref> uses dynamic programming to apply PEG rules bottom-up and right to left, which is the inverse of the normal recursive descent order of top-down, left to right. Parsing in reverse order solves the left recursion problem, allowing left-recursive rules to be used directly in the grammar without being rewritten into non-left-recursive form, and also confers optimal error recovery capabilities upon the parser, which historically proved difficult to achieve for recursive descent parsers.