[racket] Better discoverability for errortrace

I don't think that that particular message makes sense as part of the
default error messages. Specifically, if you disable errortrace in
drracket, then you wouldn't want to see those messages (or, perhaps
more accurately, you'd want to see different error messages). Maybe
the repl that racket starts up can do that, tho?

But perhaps this is something to add to xrepl?

Robby

On Mon, Sep 29, 2014 at 1:06 PM, Jonathan Schuster <schuster at ccs.neu.edu> wrote:
> We were having a discussion today in the Northeastern lab about how the
> Racket stack traces sometimes don't give enough information, and the
> solution to the problem (errrortrace) is not very discoverable if you're not
> using DrRacket.
>
> Here's an example of the kind of case I mean:
>
> $ racket -t jpg.rkt
> Assertion failed on #f
>   context...:
>    do-it
>    /Users/acobb/programs/jpg-parse/jpg.rkt:402:2: for-loop
>    decode-jpeg
>    /Users/acobb/programs/jpg-parse/jpg.rkt: [running body]
>
> $ racket -l errortrace -t jpg.rkt
> Assertion failed on #f
>   errortrace...:
>    /Users/acobb/programs/jpg-parse/jpg.rkt:126:16: (assert #f)
>    /Users/acobb/programs/jpg-parse/jpg.rkt:363:36: (huff-dc-decode dc-tree
> bits)
>    /Users/acobb/programs/jpg-parse/jpg.rkt:407:37: (reader bits)
>    <eliding for length>
>   context...:
>    huff-dc-decode
>    do-it
>    /Users/acobb/programs/jpg-parse/jpg.rkt:406:5: for-loop
>    /Users/acobb/programs/jpg-parse/jpg.rkt:402:2: for-loop
>    decode-jpeg
>    /Users/acobb/programs/jpg-parse/jpg.rkt: [running body]
>
>
> To solve the discoverability issue, what would people think of putting a
> message like "If this information is not sufficient, try errrortrace with
> racket -l errortrace -t <prog>" after the default trace? Also, can anyone
> think of a way to programmatically detect when a trace is not informative
> enough and only display the message in those cases? I haven't looked into
> the feasibility of this myself; it's just an idea that came up during our
> discussion.
>
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