Right, sorry, I should have added… doing *that* (eliminating the traces for
production code) is almost trivial: just make a macro that’s defined to
disappear when a flag is set:
#lang racket
(define-for-syntax production-flag #f)
(define-syntax (debug-only stx)
(syntax-case stx ()
[(_ expr)
(if production-flag
#'(void)
#'expr)]))
(define (fact f)
(if (= f 0)
1
(begin
(debug-only (printf "hello!\n"))
(* f (fact (- f 1))))))
(fact 6)
The hard part is building UI tools to manipulate and insert these things
without any changes to the code at all.
John
> On Mar 21, 2020, at 11:36 AM, Nicholas Papadonis
> <[email protected]> wrote:
>
> Thanks, you answered my question. I’m educating myself in ways to debug
> Scheme, coming from an imperative background.
>
> I suspect the solution would be to leave the trace statements in and use a
> conditional when delivering production code.
>
>
>> On Mar 21, 2020, at 2:27 PM, John Clements <[email protected]> wrote:
>>
>> It sounds like you’re looking for a way to have the trace inserted for you
>> by a debugging tool, so you don’t have to remember to take it out again
>> later. This wouldn’t be hard to do, but (as far as I know) no one’s taken
>> the time to do it.
>>
>> John
>>
>>> On Mar 21, 2020, at 8:43 AM, Nicholas Papadonis
>>> <[email protected]> wrote:
>>>
>>> I was successful with MIT Scheme placing (trace proc) inside the closure of
>>> this code. Placing (trace proc) outside the closure did not have any
>>> effect.
>>>
>>> This is the question I'm asking. Is it possible to trace without modifying
>>> the closure?
>>>
>>> I ask due to forward thinking about software engineering practices and
>>> modifying code (although it could be argued in C a preprocessor block could
>>> be placed to compile in or out conditional macros blocks).
>>>
>>> Thanks again
>>>
>>> On Sat, Mar 21, 2020 at 11:24 AM Ben Greenman <[email protected]>
>>> wrote:
>>> On 3/21/20, dgtlcmo <[email protected]> wrote:
>>>> Does anyone know how to trace functions inside a closure? I would like to
>>>> trace hanoi-move, however find that with MIT Scheme I need to place (trace)
>>>>
>>>> within the closure (hanoi n), otherwise the trace will not occur.
>>>>
>>>> Can a trace like this be performed in Racket?
>>>>
>>>> Thanks
>>>>
>>>> (define (hanoi n)
>>>> (define (pmd from to)
>>>> (display "Move ")
>>>> (display from)
>>>> (display " to ")
>>>> (display to)
>>>> (newline)
>>>> '())
>>>> (define (hanoi-move n from to spare)
>>>> (cond ((= n 0) '())
>>>> ((= n 1) (pmd from to))
>>>> (else
>>>> (hanoi-move (- n 1) from spare to)
>>>> (hanoi-move 1 from to spare)
>>>> (hanoi-move (- n 1) spare to from))))
>>>> (hanoi-move n "A" "B" "C"))
>>>
>>> Yes, Racket has trace tools:
>>> https://docs.racket-lang.org/reference/debugging.html
>>>
>>> Try adding (trace hanoi) before the call to (hanoi-move ....) at the bottom
>>>
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>>
>>
>>
>
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