Common Lisp isn't that esoteric!

    (defun fun-reader (stream arg)
      (declare (ignore arg))
      (read-delimited-list #\⸨ stream t))
    
    (set-macro-character #\⸨ (get-macro-character #\) nil))
    (set-macro-character #\( #'fun-reader)
    
    (defun square (x⸨
      (* x x⸨⸨
    
    (square 10⸨
    ; => 100