8.6 Review

Here is a brief summary of some recently introduced functions.

car

cdr

car returns the first element of a list; cdr returns the second and subsequent elements of a list.

For example:

(car '(1 2 3 4 5 6 7))
     ⇒ 1
(cdr '(1 2 3 4 5 6 7))
     ⇒ (2 3 4 5 6 7)

cons

cons constructs a list by prepending its first argument to its second argument.

For example:

(cons 1 '(2 3 4))
     ⇒ (1 2 3 4)

funcall

funcall evaluates its first argument as a function. It passes its remaining arguments to its first argument.

nthcdr

Return the result of taking CDR n times on a list. The “rest of the rest”, as it were.

For example:

(nthcdr 3 '(1 2 3 4 5 6 7))
     ⇒ (4 5 6 7)

setcar

setcdr

setcar changes the first element of a list; setcdr changes the second and subsequent elements of a list.

For example:

(setq triple (list 1 2 3))

(setcar triple '37)

triple
     ⇒ (37 2 3)

(setcdr triple '("foo" "bar"))

triple
     ⇒ (37 "foo" "bar")

progn

Evaluate each argument in sequence and then return the value of the last.

For example:

(progn 1 2 3 4)
     ⇒ 4

save-restriction

Record whatever narrowing is in effect in the current buffer, if any, and restore that narrowing after evaluating the arguments.

search-forward

Search for a string, and if the string is found, move point. With a regular expression, use the similar re-search-forward. (See Regular Expression Searches, for an explanation of regular expression patterns and searches.)

search-forward and re-search-forward take four arguments:

1. The string or regular expression to search for.
2. Optionally, the limit of the search.
3. Optionally, what to do if the search fails, return nil or an error message.
4. Optionally, how many times to repeat the search; if negative, the search goes backwards.

kill-region

delete-and-extract-region

copy-region-as-kill

kill-region cuts the text between point and mark from the buffer and stores that text in the kill ring, so you can get it back by yanking.

copy-region-as-kill copies the text between point and mark into the kill ring, from which you can get it by yanking. The function does not cut or remove the text from the buffer.

delete-and-extract-region removes the text between point and mark from the buffer and throws it away. You cannot get it back. (This is not an interactive command.)