Double Evaluation in $ macro

[Stardom]

Currently, the macro is defined as
;; [$ <selector-sym> <obj> <arg> ...]
(define-syntax $ ;; send [user syntax]
  (syntax-rules ()
    [($ <selector> <obj> <arg> ...)
     ;;=>
     ((-> '<selector> <obj>) <obj> <arg> ...)
    ]
) )

<obj> is repeated twice which causes double evaluation.

[Ken Dickey (ken-dickey)]

I have never seen a case in practice where a general expression is used for <obj> rather than an object reference (a variable naming an object).

It is certainly a trivial change to add the let, e.g.

(define-syntax $ ;; send [user syntax]
  (syntax-rules ()
    [($ <selector> <obj> <arg> ...)
     ;;=>
     (let [(obj <obj>)]
       ((-> '<selector> obj) obj <arg> ...))
    ]
) )

I would be interested to know the context of the problem.

Thks,
-KenD

[Stardom (seth-tewebs)]

I was doing some tests and was passing it an object which took approximately .4 seconds to compute by itself. So i was then wondering why it took .8 seconds when I directly passed the object in. Also, I imagine any function that has side effects might also create a bug in the program.

[Ken Dickey (ken-dickey)]

Fixed in revision 36 -- Thanks!