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Programming in Emacs Lisp

5.4 Review

Here is a brief summary of some of the topics covered in this chapter.

or

Evaluate each argument in sequence, and return the value of the first argument that is not nil; if none return a value that is not nil, return nil. In brief, return the first true value of the arguments; return a true value if one or any of the other are true.

and

Evaluate each argument in sequence, and if any are nil, return nil; if none are nil, return the value of the last argument. In brief, return a true value only if all the arguments are true; return a true value if one and each of the others is true.

&optional

A keyword used to indicate that an argument to a function definition is optional; this means that the function can be evaluated without the argument, if desired.

prefix-numeric-value

Convert the `raw prefix argument' produced by (interactive "P") to a numeric value.

forward-line

Move point forward to the beginning of the next line, or if the argument is greater than one, forward that many lines. If it can't move as far forward as it is supposed to, forward-line goes forward as far as it can and then returns a count of the number of additional lines it was supposed to move but couldn't.

erase-buffer

Delete the entire contents of the current buffer.

bufferp

Return t if its argument is a buffer; otherwise return nil.