stringswhere

Stringswhere is a conceptual operator in text processing and programming that filters a string by a user-specified predicate. It returns a new string composed of the characters (or, in some designs, substrings) that satisfy the predicate. The name reflects its role as a filtering step applied to sequences of characters, analogous to a where clause in databases.

Definition and variants: The core form takes a string s and a predicate p that can examine a character and optionally its index. The result is the concatenation of all characters c in s for which p(c, i) is true. Some designs also support filtering by substring properties or returning the indices of matching positions, enabling more complex analyses or transformations. Extended variants may allow the predicate to see additional context, such as the preceding or following characters.

Examples: stringswhere("hello world", (c, i) => c != " ") yields "helloworld". In many languages this can be expressed with a filter and join pattern, such as ''.join([c for i, c in enumerate(s) if pred(c, i)]) or s.filter((c, i) => pred(c, i)). The concept aligns with common map/filter idioms for strings while emphasizing shape-preserving decisions.

History and usage: Stringswhere is a theoretical construct discussed in programming language design and text-processing literature but is not a standardized library feature. Implementations appear as language-specific utilities or as part of domain-specific languages for text analysis. Its practical use mirrors other filtering operations, with attention to Unicode correctness and grapheme boundaries in real-world text.

See also: filter, map, comprehension, grapheme, substring, where clause.