Editing Parsing expression grammar (section)

=== Computational model ===
In order to attain linear overall complexity, the storage used for memoization must furthermore provide [[amortized analysis|amortized constant time]] access to individual data items memoized. In practice that is no problem — for example a dynamically sized [[hash table]] attains this – but that makes use of [[Pointer (computer programming)|pointer]] arithmetic, so it presumes having a [[random-access machine]]. Theoretical discussions of data structures and algorithms have an unspoken tendency to presume a more restricted model (possibly that of [[lambda calculus]], possibly that of [[Scheme (programming language)|Scheme]]), where a sparse table rather has to be built using trees, and data item access is not constant time. Traditional parsing algorithms such as the [[LL parser]] are not affected by this, but it becomes a penalty for the reputation of packrat parsers: they rely on operations of seemingly ill repute.

Viewed the other way around, this says packrat parsers tap into computational power readily available in real life systems, that older parsing algorithms do not understand to employ.