[racket] trace: set!: cannot mutate module-required identifier - alright .. how do you do this?

please note, the simple example here is to facilitate discussion.  trace is
being used very broadly for an entire development cycle.  This isn't a one
time fix issue in general.

I apologize if my original post wasn't clear, but I did modify the file
that included "db-lib.rkt" as such:


Saw this in another thread here, but the proposed solution didnt work,

...

so I add this to "db-citation.rkt"

    (require racket/trace)

    (trace db-exec)


And then at the prompt I get the following:

Welcome to Racket v5.2.1.

racket@> (enter! "db-citation.rkt")

db-citation.rkt:26:11: set!: cannot mutate module-required identifier in:
db-exec


Alright, so what is the magic incantation here that allows one to
debug/trace calls in included modules?

And was trying to implement Vince's solution and was asking why the above
didn't work.

I also tried going to the library source and adding at the top:

    (require racket/trace)
    (trace db-exec)

Running this again just now, I see that this gives me an error of

racket@> (enter! "db-citation.rkt")

... and own in the regression tests ..>

hooking test: drop-end-chars-test-0
link: reference (phase 0) to a variable in module
"/home/deep/src/db-lib.rkt" that is uninitialized (phase level 0);
reference appears in module: "/home/deep/src/db-citation.rkt" in: db-exec

 === context ===
/home/deep/src/db-citation.rkt: [running body]
/usr/share/racket/collects/racket/enter.rkt:33:0: do-enter!
/usr/share/racket/collects/racket/private/misc.rkt:87:7


Which is a big hint,  I moved the traces to the bottom of the file, yes and
now they work!  Thanks.

Top of the library file:

(require racket/trace)


Bottom of the library I copy all of the provides from the top, and then do
a text replace with the "provide"-> "trace" and thus:

(trace db-exec)
(trace db-rows)
...

Yes, and now calls to the library are tracing.   So to trace calls to a
library, one edits the library, puts the require at the top, copies all the
provides to the bottom, edits that to change the provides to trace, and
then off it goes.  .. could wrap the trace calls in a parameter switch
(current-db-trace) or some such...


On Mon, Jan 19, 2015 at 11:03 PM, J. Ian Johnson <ianj at ccs.neu.edu> wrote:

> To be fair, trace is more than that.
>
> Vincent's solution does work, but you have to modify the file - you can't
> do this from the REPL.
> You can modify the file containing the identifier you want to trace, if
> changing call sites is not palatable to you. Add `(require racket/trace)`
> at the top, and after the function definition `(trace function)`.
> Alternatively, if you only want to trace at given points in time, define
> and provide a function `(define (add-trace) (trace function))` so you can
> call `add-trace` when you want to turn on tracing.
>
> A missing feature for racket/trace is to provide a setter function so that
> modules that export a mutating function can be traced without depending on
> racket/trace. If a module contains a `set!` for an identifier, it disables
> any inlining for that identifier.
> e.g.
> (trace #:setter set-function!)
>
> -Ian
>
> ----- Original Message -----
> From: "Thomas Lynch" <thomas.lynch at reasoningtechnology.com>
> To: "J. Ian Johnson" <ianj at ccs.neu.edu>
> Cc: "users" <users at racket-lang.org>
> Sent: Monday, January 19, 2015 9:49:51 AM
> Subject: Re: [racket] trace: set!: cannot mutate module-required
> identifier - alright .. how do you do this?
>
> So to trace calls to the interface functions of a library I am to write a
> gasket for the library.  I may as well put a display of the args in the
> gasket functions as at this point it is the same amount of code as hooking
> the trace.   Of course then I have implemented trace.
>
> So to use trace in racket all you have to do is implement trace ..
> really??
>
> On Mon, Jan 19, 2015 at 10:06 PM, J. Ian Johnson <ianj at ccs.neu.edu> wrote:
>
> > Yes, racket 101 (305?) is that identifiers can only be set!'d in their
> > defining module. This is to allow necessary optimizations such as
> inlining.
> >
> > If you want to trace `f` from a different module. you can `(define (g .
> > args) (apply f args)) (trace g)`, use `g` wherever you use `f`. You won't
> > get any calls the library makes internally, but if you're just tracing
> for
> > your own code, you'll be golden.
> >
> > -Ian
> >
> > ----- Original Message -----
> > From: "Thomas Lynch" <thomas.lynch at reasoningtechnology.com>
> > To: "users" <users at racket-lang.org>
> > Sent: Monday, January 19, 2015 8:59:55 AM
> > Subject: [racket] trace: set!: cannot mutate module-required identifier -
> > alright .. how do you do this?
> >
> > Saw this in another thread here, but the proposed solution didnt work,
> > well at least the way I understood it. So ..
> >
> > In file db-lib.rkt I have a definition:
> >
> >
> >
> >
> > (provide db-exec)
> > (define (db-exec a) ...)
> >
> > Then in racket
> >
> >
> >
> >
> > > (enter! "db-user.rkt")
> >
> > Where db-citation.rkt has
> >
> >
> >
> >
> > (require "db-lib.rkt")
> >
> > Now at the read-eval-print prompt I try
> >
> >
> >
> >
> > (enter! "db-citation.rkt")
> >
> > And when I do (trace db-exec) I get the cannot mutate error. (Surely this
> > must be a racket 101 type problem.) So I try to include the module at the
> > current scope..
> >
> >
> >
> >
> > racket at db-citation.rkt> (require "db-lib.rkt")
> > racket at db-citation.rkt> (require racket/trace)
> > racket at db-citation.rkt> (trace db-exec)
> >
> > racket at db-citation.rkt> stdin::1130: set!: cannot mutate module-required
> > identifier in: db-exec
> > ok, so that doesn't work, so I start over again. This time after reading
> > the thread on this list
> >
> >
> >
> >
> > From: Vincent St-Amour (stamourv at ccs.neu.edu )
> > Date: Mon Oct 10 13:49:46 EDT 2011
> >
> > which concludes by saying 'put the trace in your program that should
> > work', so I add this to "db-citation.rkt"
> >
> >
> >
> >
> > (require racket/trace)
> > (trace db-exec)
> >
> > And then at the prompt I get the following:
> >
> >
> >
> >
> > Welcome to Racket v5.2.1.
> > racket@> (enter! "db-citation.rkt")
> > db-citation.rkt:26:11: set!: cannot mutate module-required identifier in:
> > db-exec
> >
> > Alright, so what is the magic incantation here that allows one to
> > debug/trace calls in included modules?
> >
> > Thanks!
> >
> > Thomas
> >
> > ____________________
> >   Racket Users list:
> >   http://lists.racket-lang.org/users
> >
>
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