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Common Lisp the Language, 2nd Edition
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Up: Type Specifiers
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Lists
A type specifier list
(satisfiespredicate-name)
denotes the set of all objects that satisfy the predicate named by
predicate-name, which must be a symbol whose global function
definition is a one-argument predicate. (A name is required;
lambda-expressions are disallowed in order to avoid scoping problems.)
For example, the type (satisfies numberp) is the same as
the type number. The call
(typep x '(satisfies p)) results in applying p
to x and returning t if the result is true and
nil if the result is false.
As an example, the type string-char could be defined as
(deftype string-char ()
'(and character (satisfies string-char-p)))See deftype.
X3J13 voted in March 1989 (COMMON-TYPE) to remove the type
string-char and the function string-char-p
from the language.
It is not a good idea for a predicate appearing in a
satisfies type specifier to cause any side effects when
invoked.
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