Characterswhile

Characterswhile is a conceptual term used in computer science to describe an operation that consumes characters from a string or stream while a given predicate holds for each character. It is not an official keyword in mainstream programming languages, but it is used informally to discuss a common pattern in lexical analysis and text processing.

Formal definition and behavior

Given a string s and a predicate P(character) that returns true or false, characterswhile(s, P) returns the longest prefix of s consisting of characters for which P holds. In practice, it scans characters from the start of s until it encounters a character for which P is false, and then returns the collected prefix. For example, characterswhile("abc123", isLetter) yields "abc", because the letters stop at the first non-letter.

Algorithmic outline

- Initialize a position index at the start of the string.

- While the current character satisfies P, advance the index.

- Return the substring from the start up to (but not including) the first non-satisfying character.

Applications and variants

Characterswhile is commonly used in tokenization, parsing, and validation tasks to extract runs of characters that match a rule (e.g., letters, digits, whitespace). Variants may apply the predicate to the next character, a stream of input, or to a character class. It is closely related to the concept of scanning in regular expressions and lexical analysis.

See also

- while loop

- tokenization

- lexical analysis

- prefix extraction

- string processing