Question

I want to write a small function to add a value to a list. it looks like this:

(defvar fares '(31.14 28.12 25.10 22.08 19.06 16.04 13.02 10))

(defun plus-extra (fare) (+ 3.02 fare))

(map 'plus-extra fares)

Fairly predictably, the elisp barfs because the function needs an argument. What am I missing?

Thanks
Robert

Answer 1

The function which doesn’t have enough argument here is map, not the one you defined.

The map function does not exists in Emacs Lisp, it is provided by the cl package. This map function require 3 arguments, the first one must be the type of what map should return. This:

(map 'list 'plus-extra fares)

will work. But what you want is this:

(mapcar 'plus-extra fares)

which is native elisp.

PS: Don’t forget that Emacs comes with its documentation! C-h f map RET ;-).