In this article we will be exploring what parser combinators are, what runtime parser generation is - why they’re useful, and then walking through a Zig implementation of them.

• What are parser combinators?
• A note about traditional regex engines
• Our first parser combinator
• Using our OneOf parser combinator
• Runtime parser generation
• Closing thoughts

What are parser combinators?

A parser parses some text to produce a result:

A parser combinator is a higher-order function which takes parsers as input and produces a new parser as output:

Why are parser combinators useful?

Let’s say we want to parse the syntax which describes a regular expression: a[bc].*abc

We can define some parsers to help us parse this syntax (e.g. into tokens or AST nodes):

Suppose that for a[bc].*abc :

• RegexLiteralParser can parse a, b, and c, but not abc (the string.)
• RegexRangeOpenParser can parse [.
• RegexRangeCloseParser can parse ]
• RegexAnyParser can parse the . “any character” syntax.