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Just as functions in other programming languages are executable,
Lisp function objects are pieces of executable code. However,
functions in Lisp are primarily Lisp objects, and only secondarily the
text which represents them. These Lisp objects are lambda expressions:
lists whose first element is the symbol lambda (see section Lambda Expressions).
In most programming languages, it is impossible to have a function without a name. In Lisp, a function has no intrinsic name. A lambda expression is also called an anonymous function (see section Anonymous Functions). A named function in Lisp is actually a symbol with a valid function in its function cell (see section Defining Named Functions).
Most of the time, functions are called when their names are written in
Lisp expressions in Lisp programs. However, a function object found or
constructed at run time can be called and passed arguments with the
primitive functions funcall and apply. See section Calling Functions.
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