eintr: Sample let Expression
3.6.2 Sample ‘let’ Expression
-----------------------------
The following expression creates and gives initial values to the two
variables ‘zebra’ and ‘tiger’. The body of the ‘let’ expression is a
list which calls the ‘message’ function.
(let ((zebra "stripes")
(tiger "fierce"))
(message "One kind of animal has %s and another is %s."
zebra tiger))
Here, the varlist is ‘((zebra "stripes") (tiger "fierce"))’.
The two variables are ‘zebra’ and ‘tiger’. Each variable is the
first element of a two-element list and each value is the second element
of its two-element list. In the varlist, Emacs binds the variable
‘zebra’ to the value ‘"stripes"’(1), and binds the variable ‘tiger’ to
the value ‘"fierce"’. In this example, both values are strings. The
values could just as well have been another list or a symbol. The body
of the ‘let’ follows after the list holding the variables. In this
example, the body is a list that uses the ‘message’ function to print a
string in the echo area.
You may evaluate the example in the usual fashion, by placing the
cursor after the last parenthesis and typing ‘C-x C-e’. When you do
this, the following will appear in the echo area:
"One kind of animal has stripes and another is fierce."
As we have seen before, the ‘message’ function prints its first
argument, except for ‘%s’. In this example, the value of the variable
‘zebra’ is printed at the location of the first ‘%s’ and the value of
the variable ‘tiger’ is printed at the location of the second ‘%s’.
---------- Footnotes ----------
(1) According to Jared Diamond in ‘Guns, Germs, and Steel’, “...
zebras become impossibly dangerous as they grow older” but the claim
here is that they do not become fierce like a tiger. (1997, W. W.
Norton and Co., ISBN 0-393-03894-2, page 171)
Info Catalog
eintr: Parts of let Expression
eintr: let
eintr: Uninitialized let Variables