eintr: Args as Variable or List
1.8.2 An Argument as the Value of a Variable or List
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An argument can be a symbol that returns a value when it is evaluated.
For example, when the symbol ‘fill-column’ by itself is evaluated, it
returns a number. This number can be used in an addition.
Position the cursor after the following expression and type ‘C-x
C-e’:
(+ 2 fill-column)
The value will be a number two more than what you get by evaluating
‘fill-column’ alone. For me, this is 74, because my value of
‘fill-column’ is 72.
As we have just seen, an argument can be a symbol that returns a
value when evaluated. In addition, an argument can be a list that
returns a value when it is evaluated. For example, in the following
expression, the arguments to the function ‘concat’ are the strings
‘"The "’ and ‘" red foxes."’ and the list ‘(number-to-string (+ 2
fill-column))’.
(concat "The " (number-to-string (+ 2 fill-column)) " red foxes.")
If you evaluate this expression—and if, as with my Emacs, ‘fill-column’
evaluates to 72—‘"The 74 red foxes."’ will appear in the echo area.
(Note that you must put spaces after the word ‘The’ and before the word
‘red’ so they will appear in the final string. The function
‘number-to-string’ converts the integer that the addition function
returns to a string. ‘number-to-string’ is also known as
‘int-to-string’.)
Info Catalog
eintr: Data types
eintr: Arguments
eintr: Variable Number of Arguments