Use of # a.k.a. read-macro

Question

Reading book \"Let Over Lambda\" by Doug Hoyte, I found the following description of #. sign, a.k.a. read-macro:

A basic read macro that come

Answer 1

You can call global definitions of functions both ways:

CL-USER> (defun test nil t)
TEST
CL-USER> (funcall #'test)
T
CL-USER> (funcall 'test)
T

But see this:

CL-USER 10 > (defun foo () 42)
FOO

CL-USER 11 > (flet ((foo () 82))
               (print (foo))
               (print (funcall 'foo))
               (print (funcall #'foo)))

82   ; the local definition
42   ; the symbol references the global definition
82   ; (function foo) / #'foo  references the local definition

(funcall 'foo) looks up the function from the symbol.

(funcall #'foo) calls the function from the lexical environment. If there is none the global definition is used.

#'foo is a shorthand notation for (function foo).

CL-USER 19 > '#'foo
(FUNCTION FOO)