Cases galore

(defun hippo (long-side short-side &key (directions '(:f :b :r :l)))
  (cond
    ;; degenerate cases
    ((< long-side short-side) (hippo short-side long-side :directions directions :jump-distance jump-distance))
    ((= long-side short-side) (diagonal-jump :directions directions :jump-distance long-side))
    ((zerop short-side)     (orthogonal-jump :directions directions :jump-distance long-side))
    ;; the real thing
    (t (flet ((decode-hippogonals (dir) ;keyword shorthand expansion
        (loop for i in dir
           append (case i
                (:f   (list :ffr :ffl :fsr :fsl))
                (:b   (list :bbr :bbl :bsr :bsl))
                (:r   (list :ffr :fsr :bsr :bbr))
                (:l   (list :ffl :fsl :bsl :bbl))
                (:fr  (list :ffr :fsr))
                (:fl  (list :ffl :fsl))
                (:br  (list :bbr :bsr))
                (:bl  (list :bbl :bsl))
                (:ff  (list :ffr :ffl))
                (:fs  (list :fsr :fsl))
                (:bb  (list :bbr :bbl))
                (:bs  (list :bsr :bsl))
                (:ll  (list :bsl :fsl))
                (:lv  (list :bbl :ffl))
                (:rr  (list :bsr :fsr))
                (:rv  (list :bbr :ffr))
                (:fb  (list :ffl :ffr :bbl :bbr))
                (:rl  (list :fsl :fsr :bsl :bsr))
                (:ffr (list :ffr))
                (:fsr (list :fsr))
                (:bsr (list :bsr))
                (:bbr (list :bbr))
                (:bbl (list :bll))
                (:bsl (list :bsl))
                (:fsl (list :fsl))
                (:ffl (list :ffl))))))
     (let ((vectors (list :ffr (dest (+ short-side) (+ long-side) )
                  :fsr (dest (+ long-side)  (+ short-side))
                  :bsr (dest (+ long-side)  (- short-side))
                  :bbr (dest (+ short-side) (- long-side) )
                  :bbl (dest (- short-side) (- long-side) )
                  :bsl (dest (- long-side)  (- short-side))
                  :fsl (dest (- long-side)  (+ short-side))
                  :ffl (dest (- short-side) (+ long-side)))))
       (remove-duplicates (mapcar #'(lambda (x) (getf vectors x)) (expand-hippogonals directions))))))))