CODEWITHSUNDEEP
emacslispelisp
robertpostill
robertpostill

Reputation: 3970

How do I pass arguments to map in emacs lisp?

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

Upvotes: 8

Views: 2512

Answers (2)

p4bl0
p4bl0

Reputation: 3906

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 ;-).

Upvotes: 16

sanityinc
sanityinc

Reputation: 15212

Use mapcar, not map. With mapcar, your example yields:

(34.160000000000004 31.14 28.12 25.099999999999998 22.08 19.06 16.04 13.02)

If you M-x describe-function RET map RET, you'll see the signature of map is not what you expected:

(map TYPE FUNCTION SEQUENCE...)

Map a FUNCTION across one or more SEQUENCEs, returning a sequence.
TYPE is the sequence type to return.

Upvotes: 7

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