Portability library for detecting reader errors coming from reading non-existing or non-external symbols in packages
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This is a minor portability library that allows the user to check if a condition has been signaled due to trying to read a non-existing or non-external symbol of a package when the foo:bar notation was used.

These two test cases illustrate the condition that would be signaled:

(make-package 'foo :use nil)
(read-from-string "foo:bar")
(make-package 'foo :use nil)
(intern "BAR" 'foo)
(read-from-string "foo:bar")

Note that EXTERNAL-SYMBOL-NOT-FOUND is a Common Lisp type but it is not a Common Lisp condition type.

You cannot create new instances of this condition, but you can refer to already existing instances created by your Lisp implementation using this type; most importantly, this type is valid for usage in HANDLER-CASE, HANDLER-BIND and other similar macros where it is required to specify a type for later type matching.

Supported implementations

Implemented for and tested on:

  • SBCL 1.4.6
  • CCL 1.11.5
  • ABCL 1.5.0
  • ECL 16.1.2

On all other implementations, the system will load, but using any of this project's functionality will signal an error.

Adding support for other implementations is easy. If you do not want to do it yourself, please make an issue on this project along with the output of the following Lisp form:

(handler-case (progn
                (unless (find-package 'temp)
                  (make-package 'temp :use nil))
                (read-from-string "temp:symbol"))
  (error (e)
    (format t "~A~%" e)
    (describe e)
    (describe (class-of e))))


  • Type EXTERNAL-SYMBOL-NOT-FOUND - denotes conditions signaled when the Lisp reader encountered a non-existing external symbol of a package.
  • Predicate EXTERNAL-SYMBOL-NOT-FOUND-P - returns true iff the condition is of type EXTERNAL-SYMBOL-NOT-FOUND.
  • Function EXTERNAL-SYMBOL-NOT-FOUND-SYMBOL-NAME - retrieves the symbol name from the condition instance.
  • Function EXTERNAL-SYMBOL-NOT-FOUND-PACKAGE - retrieves the package object from the condition instance.


Unlicense. Do whatever you want with it, the code is here to be useful.