Editing Operator-precedence parser (section)

== Relationship to other parsers ==

An operator-precedence parser is a simple [[shift-reduce parser]] that is capable of parsing a subset of [[LR parser|LR(1)]] grammars.  More precisely, the operator-precedence parser can parse all LR(1) grammars where two consecutive [[nonterminal]]s and [[empty string|epsilon]] never appear in the right-hand side of any rule.

Operator-precedence parsers are not used often in practice;  however they do have some properties that make them useful within a larger design.  First, they are simple enough to write by hand, which is not generally the case with more sophisticated right shift-reduce parsers.  Second, they can be written to consult an operator table at [[Run time (program lifecycle phase)|run time]], which makes them suitable for languages that can add to or change their operators while parsing. (An example is [[Haskell (programming language)|Haskell]], which allows user-defined infix operators with custom associativity and precedence; consequently, an operator-precedence parser must be run on the program ''after'' parsing of all referenced modules.)

[[Raku (programming language)|Raku]] sandwiches an operator-precedence parser between two [[recursive descent parser]]s in order to achieve a balance of speed and dynamism. [[GNU Compiler Collection|GCC]]'s C and C++ parsers, which are hand-coded recursive descent parsers, are both sped up by an operator-precedence parser that can quickly examine arithmetic expressions.  Operator-precedence parsers are also embedded within [[compiler-compiler]]-generated parsers to noticeably speed up the recursive descent approach to expression parsing.<ref name="Harwell2008">{{cite web| last=Harwell | first=Sam | date=2008-08-29 | title=Operator precedence parser | url=https://theantlrguy.atlassian.net/wiki/spaces/ANTLR3/pages/2687077/Operator+precedence+parser | publisher=ANTLR3 Wiki | access-date=2017-10-25}}</ref>