An algorithm that performs tokenization and parsing in a single step
In computer science, scannerless parsing (also called lexerless parsing) performs tokenization (breaking a stream of characters into words) and parsing (arranging the words into phrases) in a single step, rather than breaking it up into a pipeline of a lexer followed by a parser, executing concurrently. A language grammar is scannerless if it uses a single formalism to express both the lexical (word level) and phrase level structure of the language.
Dividing processing into a lexer followed by a parser is more modular; scannerless parsing is primarily used when a clear lexer–parser distinction is unneeded or unwanted. Examples of when this is appropriate include TeX, most wiki grammars, makefiles, simple application-specific scripting languages, and Raku.
