check-type

(check-type place typespec [string])

Evaluates place and signals an error when the value is not of the given type; returns nil when it is. This is the lite version of Common Lisp's check-type: there is no restart system, so the error cannot be corrected interactively and the place is never re-stored.

Supported type specifiers are the typecase type names (integer, float, number, rational, string, symbol, keyword, cons, list, null, atom, character, hash-table, boolean) plus the compound forms (or ...), (and ...), (not ...), (member item...), (eql object), (satisfies function), and ranged numeric types like (integer 0 9) (* means unbounded and a (bound) list is exclusive). The optional string replaces the "of type ..." part of the error message.

A failing check aborts execution, so it is shown statically:

(let ((n 12)) (check-type n (integer 0 9)))
; error: The value of n is 12, which is not of type (integer 0 9).