Combinator parsing is a technique used in computer science to build parsers for formal languages. It involves combining small parsing functions, called combinators, to create more complex parsers that can handle a wide range of input patterns.

In combinator parsing, a parser is essentially a function that takes an input string and produces a parse tree or some other form of structured representation of the input. Combinators are higher-order functions that take parsers as input and return a new parser as output. They allow parsers to be combined and composed in a modular and flexible way.

There are different types of combinators used in combinator parsing, including:

1. Sequence Combinators: These combinators allow parsers to be executed sequentially. For example, a sequence combinator might take two parsers as input and return a new parser that matches the first parser, followed by the second parser.

2. Choice Combinators: Choice combinators allow parsers to match one of several alternatives. For example, a choice combinator might take two parsers as input and return a new parser that matches either the first parser or the second parser.

3. Transformation Combinators: Transformation combinators modify the output of a parser. They can be used to convert the parsed input into a different representation or perform other transformations on the parsed data.

By combining these basic combinators, complex parsers can be built that can handle a variety of input patterns and grammars. Combinator parsing libraries provide a set of predefined combinators along with mechanisms for creating custom combinators.

The advantage of combinator parsing is its simplicity and modularity. Combinator parsers are often easy to understand and maintain because they are built from small, reusable components. Combinator parsing also allows for incremental development, as parsers can be built step by step by combining and refining smaller parsers.

Combinator parsing is widely used in the development of programming language compilers, interpreters, and other systems that require parsing and analyzing input languages. It provides a flexible and expressive approach to parsing that can accommodate a wide range of language grammars and input patterns.
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