(if test then-clause else-clause)

Executes and returns the value of then-clause if test is not zero; otherwise it executes else-clause if it is present.

Example: Tab to column 33 if dot is currently at the start of a line:

(if (bolp)
    (to-col 33)
)

You can also have multiple tests, which gives you the equivalent of switch or case statements in other programming languages:

(defun
    (month
        response
        (setq response (get-tty-string "Month number: "))
        (if
            (= response 1)
            (insert-string "January")
            (= response 2)
            (insert-string "February")
            (= response 3)
            (insert-string "March"))
        )                   ; if
    )
)

(illegal-operation) All keys not currently bound

illegal-operation is bound to those keys that do not have a defined interpretation. Executing illegal-operation is an error.

(incremental-search) ^F

Start incremental search in forward search mode. See extension incsearch for details

(indent-C-procedure) ESC-j

Locates the current C language procedure and passes it as the standard input to the INDENT program. The resulting indented C procedure will replace the initial C procedure. The old text is temporarily stored in Kill buffer.

(insert-character expression)

Inserts its numeric argument into the buffer as a single character prefix-argument times.

Example: Each of the following inserts a zero into the current buffer:

(insert-character 48)

(insert-character '0')

(insert-file file-name) ^X-^I

Inserts the specified file's contents at dot in the current buffer.

See also:

(insert-string expression)

Inserts the string that results from evaluating the given expression. insert-string concatenates multiple string arguments.

Examples:

Insert the current date and time into the current buffer:

(insert-string (current-time))

Insert the current time and buffer name:

(insert-string "Time:   " (current-time) "\nBuffer: " (current-buffer-name) "\n") 

Sample output from this line:

Time:   Tue Sep 28 10:48:41 1999
Buffer: fred

(interactive)

Returns 1 if the invoking MLisp function was called interactively.

(interrupt-key) ^G

When bound to a single key causes any current activity within Emacs to be aborted, and forces Emacs to accept commands from the keyboard when that key is struck.

Binding interrupt-key to a sequence longer than one character does not allow the key sequence to interrupt Emacs. Only single key sequences can be used for interrupting.

(is-bound variable-name...)

Returns 1 if all of its variable name arguments are bound to some storage.

(is-function string)

Checks that its string parameter is a defined function. It returns 1 if it is defined and 0 otherwise.

You can use this function to determine whether a function is defined before attempting to execute it.