Next: Loop Up: Miscellaneous Features Previous: Other Environment Inquiries
Common Lisp the Language, 2nd Edition
Next: Loop
Up: Miscellaneous Features
Previous: Other Environment
Inquiries
This function is occasionally useful as an argument to other functions that require functions as arguments. (Got that?)
[Function]
identityobject
The object is returned as the value of
identity.
The identity function is the default value for the
:key argument to many sequence functions (see chapter 14).
Table 12-1 illustrates the
behavior in the complex plane of the identity function
regarded as a function of a complex numerical argument.
Many other constructs in Common Lisp have the behavior of
identity when given a single argument. For example, one
might well use values in place of identity.
However, writing values of a single argument conventionally
indicates that the argument form might deliver multiple values and that
the intent is to pass on only the first of those values.
Compatibility note: In Maclisp, progn
was a function of any number of arguments that returned its last
argument, so progn could be used as an identity function.
In Common Lisp, progn is a special form and therefore
cannot be used for that purpose.
AI.Repository@cs.cmu.edu