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| ANSI Common Lisp 4 Types and Classes 4.4 Dictionary of Types and Classes
4.4.30 type-error-datum, type-error-expected-type | Function
  Syntax: type-error-datum condition datum type-error-expected-type condition expected-type Arguments and Values: condition - a condition of type type-error. datum - an object. expected-type - a type specifier. Description: type-error-datum returns the offending datum in the situation represented by the condition. type-error-expected-type returns the expected type of the offending datum in the situation represented by the condition. Examples:
       (defun fix-digits (condition)
         (check-type condition type-error)
         (let* ((digits '(zero one two three four
                         five six seven eight nine))
               (val (position (type-error-datum condition) digits)))
           (if (and val (subtypep 'fixnum (type-error-expected-type condition)))
               (store-value 7))))

       (defun foo (x)
         (handler-bind ((type-error #'fix-digits))
           (check-type x number)
           (+ x 3)))

       (foo 'seven)
       10
See Also: type-error, Conditions Allegro CL Implementation Details: None.

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