;;; in Arc + is defined

;;; macro writers code depends on Arc's + ;;; but doesn't insure it always uses Arc's +

(mac foo () (list '+ 1 2))

;;; app writers code

(* 2 (foo)) ;;; 6

;;; app writer doesn't know foo depends on Arc's + ;;; and decides to redefine +

(= + (fn ((o x) (o y)) (prn "gotcha")))

(* 2 (foo)) ;;; error

;;;;;;;;;;;;;;;;;; the following works ;;;;;;;;;;;;;;;;;;;;

;;; in Arc + is defined

;;; macro writers code is tricky and ugly ;;; but will always use Arc's +

(= g (uniq))

(eval (list '= g '+))

(eval (list 'mac 'foo `() `(list (quote ,g) 1 2)))

;;; app writers code

(* 2 (foo)) ;;; 6

;;; redefining + doesn't affect the addtion function ;;; used in the foo macro

(= + (fn ((o x) (o y)) (prn "gotcha")))

(* 2 (foo)) ;;; 6

;;;;;;;;;;;; if foo is a function then it is easy ;;;;;;;;;;

;;; in Arc + is defined

;;; library writers code is easy because ;;; the original + can be in a closure

(= foo ((fn () (let plus + (fn () (plus 1 2))))))

;;; app writers code

(* 2 (foo)) ;;; 6

;;; redefining + doesn't affect the addtion function ;;; used in the foo function

(= + (fn ((o x) (o y)) (prn "gotcha")))