Short names are addictive

This morning I tried to do this in Common Lisp:

(defun neighbors (x y)
  (mapcar (fn (dx dy) (vector (+ x dx) (+ y dy)))
          '(-1 0 1 0)
          '(0 1 0 -1)))

Naturally, SBCL spit out half a page of warnings, starting with this:

;     (+ X DX)
; caught WARNING:
;   undefined variable: DX

;     (DX DY)
;   undefined function: DX
; caught WARNING:
;   undefined variable: DY

It took me an embarassingly long time to figure out why. I have become so used to fn being lambda - in Arc, Clojure, and any number of other new Lisps, including my own - that I didn't notice anything out of the ordinary.

I did at least remember that CL can't add vectors, which was how I wanted to write it. This is a hazard of learning new languages, and of designing them: improvements, even such minor ones as shorter names, are addictive. They're fun at first, but soon you become dependent on them, and the old ways seem unbearably clunky, if you can even remember them.

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