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== Advantages ==
=== No compilation required ===
Many parsing algorithms require a preprocessing step where the grammar is first compiled into an opaque executable form, often some sort of automaton. Parsing expressions can be executed directly (even if it is typically still advisable to transform the human-readable PEGs shown in this article into a more native format, such as [[Lisp (programming language)#Symbolic_expressions_(S-expressions)|S-expressions]], before evaluating them).
=== Compared to regular expressions ===
Compared to pure [[regular expressions]] (i.e., describing a language recognisable using a [[finite automaton]]), PEGs are vastly more powerful. In particular they can handle unbounded recursion, and so match parentheses down to an arbitrary nesting depth; regular expressions can at best keep track of nesting down to some fixed depth, because a finite automaton (having a finite set of internal states) can only distinguish finitely many different nesting depths. In more theoretical terms, <math> \{a^n b^n\}_{n \geqslant 0} </math> (the language of all strings of zero or more <math>a</math>'s, followed by an ''equal number'' of <math>b</math>s) is not a regular language, but it is easily seen to be a parsing expression language, matched by the grammar
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