Standard Common Lisp functions implemented using generic functions.

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Alexander Gutev




GENERIC-CL provides a generic function wrapper over various functions in the Common Lisp standard, such as equality predicates and sequence operations. The goal of this wrapper is to provide a standard interface to common operations, such as testing for the equality of two objects, which is extensible to user-defined types.


In Common lisp you have a number of different equality comparison functions for different object types. Worse still you have to invent a new name for the comparison functions for each of your own object types.

Standard Common Lisp:

(eq 'a x)           ;; Symbols
(= 1 2)             ;; Numbers
(equal '(1 2 3) x)  ;; Lists
(equal "hello" y)   ;; Strings
(equalp #(1 2 3) z) ;; Arrays

(foo-equal x y)     ;; Instances of class foo

In GENERIC-CL there is a single equality predicate = which can be used on objects of any builtin type. Since it's implemented using generic functions, it can be extended with methods for user-defined classes and structures.


(= 'a x)       ;; Symbols
(= 1 2)        ;; Numbers
(= '(1 2 3) x) ;; Lists
(= "hello" y)  ;; Strings
(= #(1 2 3) z) ;; Arrays

(= x y)        ;; Instances of class foo

GENERIC-CL also provides generic interfaces for comparison (<, >, ...) functions, copying objects, iteration, sequence operations, hash-tables capable of storing keys of user defined classes, and many more.


Full documentation is available online in HTML format at, and also in AsciiDoc format in the doc/ folder.

Isn't this slow?

Generic functions do carry an additional overhead over ordinary functions, however this isn't a significant issue for most applications.

For those applications where the speed of generic-functions is an issue, generic function calls can be optimized, using static-dispatch on which this library is built, to be as efficient (and sometimes even more efficient) as ordinary function calls, when the types of the arguments are known at compile-time. Check out the Optimization section for more information.

Dependencies (10)

  • agutil
  • alexandria
  • anaphora
  • arrows
  • cl-custom-hash-table
  • cl-form-types
  • fiveam
  • parse-declarations
  • static-dispatch
  • trivia
  • GitHub
  • Quicklisp