elisp betweenマクロ

between.el

(defmacro between (var start end &optional $=)
  `(cond ((null ,var) nil)
         ((numberp ,var)
          (let (($$ (if ,$= '<= '<)))
            (and (funcall $$ ,start ,var) (funcall $$ ,var ,end))))
         ((stringp ,var)
          (if ,$=
              (or (and (string< ,start ,var) (string< ,var ,end)) (string= ,start ,var) (string= ,var ,end))
            (and (string< ,start ,var) (string< ,var ,end))))
         (t (error "comparing neither numberp nor stringp"))))

; (let ((n "b"))
;   (between n "a" "c"))
; =>t
; (let ((n "a"))
;   (between n "a" "c"))
; =>nil
; (let ((n "a"))
;   (between n "a" "c" t))
; =>t
; (let ((n 3))
;   (between n 1 3))
; =>nil
; (let ((n 3))
;   (between n 1 3 t))
; =>t
; (let ((n "a"))
;   (between n 1 3))
; =>error