Defining aliases to standard Common Lisp functions?

Question

Lisp is said to enable redefinitions of its core functions. I want to define an alias to the function cl:documentation function, such that

(doc 'write 'function) === (documentation 'write 'function)

How can this be done and made permanent in SBCL?

Answer 1

Creating an Alias

You are not trying to redefine (i.e., change the definition of) the system function documentation, you want to define your own function with a shorter name which would do the same thing as the system function.

This can be done using fdefinition:

 (setf (fdefinition 'doc) #'documentation)

How to make your change "permanent" in common lisp

There is no standard way, different implementation may do it differently, but, generally speaking, there are two common ways.

Add code to an init file - for beginners and casual users

• SBCL
• CLISP
• Clozure
• ECL

The code in question will be evaluated anew every time lisp starts.

Pro:

• Easy to modify (just edit file)
• Takes little disk space
• Normal lisp invocation captures the change

Con:

• Evaluated every time you start lisp (so, slows start up time if the code is slow)

Save image - for heavy-weight professionals

• SBCL
• CLISP
• Clozure
• ECL - not supported

The modified lisp world is saved to disk.

Pro:

• Start uptime is unaffected

Con:

• Requires re-dumping the world on each change
• Lisp image is usually a large file (>10MB)
• Must specify the image at invocation time

Answer 2

Even though @sds has already answered pretty thoroughly I just wanted to add that the utility library serapeum has defalias

Answer 3

I use a simple macro for this:

(defmacro alias (to fn)
    `(setf (fdefinition ',to) #',fn))

e.g.

(alias neg -) => #<Compiled-function ... >

(neg 10) => -10

Other answers include detail about how to make this permanent.