stringp

Stringp is a predicate function in Lisp-family languages used to test whether a given object is a string. In Common Lisp, (stringp x) returns true (T or non-nil) if x is an instance of the built-in string type, and nil otherwise. The function does not attempt to coerce or convert the argument; it purely reports whether the argument is already a string. For practical purposes, stringp is often used as a convenient shorthand for a type check, similar in effect to (typep x 'string).

Examples:

- (stringp "hello") => T

- (stringp 123) => NIL

- (stringp (make-string 5 :initial-element #\a)) => T

Usage and patterns:

- String validation: (when (stringp s) ... ) to execute code only for strings.

- Conditional branches can rely on stringp to distinguish strings from other object types in input handling and data processing.

Dialect notes:

- In Common Lisp, stringp is a standard, built-in predicate and is widely used in conjunction with other type predicates.

- In some other Lisp dialects, the analogous check may be provided by a different name (for example, string? in Scheme), but many Common Lisp environments expose stringp directly.

- See also typep, string, and make-string for related type and string operations.

Overall, stringp provides a concise, reliable way to confirm that a value is a string before performing string-specific operations.