type-error-datum condition → datum

type-error-expected-type condition → expected-type

condition — a condition of type type-error.

datum — an object.

expected-type — a type specifier.

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.

 (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

type-error, Chapter 9 (Conditions)