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print-not-readable-object

print-not-readable-object Function

Syntax:

print-not-readable-object condition ! object

Arguments and Values:

condition—a condition of type print-not-readable.

object—an object.

Description:

Returns the object that could not be printed readably in the situation represented by condition.

See Also:

print-not-readable, Chapter 9 (Conditions)

Expanded Reference: print-not-readable-object​

Retrieving the Unprintable Object​

print-not-readable-object takes a condition of type print-not-readable and returns the object that could not be printed readably.

(handler-case
    (let ((*print-readably* t))
      (write-to-string *standard-output*))
  (print-not-readable (c)
    (let ((obj (print-not-readable-object c)))
      (format nil "Cannot print ~A readably" (type-of obj)))))
;; => "Cannot print SYNONYM-STREAM readably"  ; type is implementation-dependent

Using in Error Handling​

(handler-case
    (let ((*print-readably* t))
      (write-to-string (make-hash-table)))
  (print-not-readable (c)
    (let ((obj (print-not-readable-object c)))
      (format nil "Object of type ~S is not printable readably"
              (type-of obj)))))
;; => "Object of type HASH-TABLE is not printable readably"
;; Note: SBCL can print hash tables readably using #. syntax

The Object Is the Same Identity​

The returned object is the same (by eq) as the object that was being printed when the error was signaled.

(let ((ht (make-hash-table)))
  (handler-case
      (let ((*print-readably* t))
        (write-to-string ht))
    (print-not-readable (c)
      (eq ht (print-not-readable-object c)))))
;; => T  ; SBCL can print hash tables readably, so handler-case is not entered