Parsing Algorithm Comparison Essay

LR parsers IMHO can be the fastest. Basically they use a token as an index into a lookahead set or a transition table to decide what to do next (push a state index, pop a state indexes/call a reduction routine). Converted to machine code this can just a few machine instructions. Pennello discusses this in detail in his paper:

Thomas J. Pennello: Very fast LR parsing. SIGPLAN Symposium on Compiler Construction 1986: 145-151

LL parsers involve recursive calls, which are a bit slower than just plain table lookups, but they can be pretty fast.

GLR parsers are generalizations of LR parsers, and thus have to be slower than LR parsers. A key observation is that most of the time a GLR parser is acting exactly as an LR parser would, and one can make that part run essentially as the same speed as an LR parser, so they can be fairly fast.

Your parser is likely to spend more time breaking the input stream into tokens, than executing the parsing algorithm, so these differences may not matter a lot.

In terms of getting your grammar into a usable form, the following is the order in which the parsing technologies "make it easy":

  • GLR (really easy: if you can write grammmar rules, you can parse)
  • LR(k) (many grammars fit, extremely few parser generators)
  • LR(1) (most commonly available [YACC, Bison, Gold, ...]
  • LL (usually requires significant reengineering of grammar to remove left recursions)
  • Hand-coded recursive descent (easy to code for simple grammars; difficult to handle complex grammars and difficult to maintain if the grammar changes a lot)

In computer science, a chart parser is a type of parser suitable for ambiguous grammars (including grammars of natural languages). It uses the dynamic programming approach—partial hypothesized results are stored in a structure called a chart and can be re-used. This eliminates backtracking and prevents a combinatorial explosion.

Chart parsing is generally credited to Martin Kay.[1]

Types of chart parsers[edit]

A common approach is to use a variant of the Viterbi algorithm. The Earley parser is a type of chart parser mainly used for parsing in computational linguistics, named for its inventor. Another chart parsing algorithm is the Cocke-Younger-Kasami (CYK) algorithm.

Chart parsers can also be used for parsing computer languages. Earley parsers in particular have been used in compiler compilers where their ability to parse using arbitrary Context-free grammars eases the task of writing the grammar for a particular language. However their lower efficiency has led to people avoiding them for most compiler work.

In bidirectional chart parsing, edges of the chart are marked with a direction, either forwards or backwards, and rules are enforced on the direction in which edges must point in order to be combined into further edges.

In incremental chart parsing, the chart is constructed incrementally as the text is edited by the user, with each change to the text resulting in the minimal possible corresponding change to the chart.

Chart parsers are distinguished between top-down and bottom-up, as well as active and passive.

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