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Re: Assertions in Mathematica?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg113455] Re: Assertions in Mathematica?
  • From: James Stein <mathgroup at stein.org>
  • Date: Fri, 29 Oct 2010 06:29:11 -0400 (EDT)

Below is the content of a cell I include in most projects.
I think 'abort' does what you wish, and also maintains a log of aborts.
'fail' is the same, except that since it does not call 'Abort', it can be
deployed in a suite of tests.
Hope this helps.

ClearAll[abort, abortLog, fail, failLog];
abortLog = failLog = {};
abort[s__] := (Beep[];
   AppendTo[abortLog, {s}];
   Print["Aborting: ", s];
   Abort[]);
fail[s__] := (Beep[];
   AppendTo[failLog, {s}];
   Print["Fail: ", s]
   );

On Thu, Oct 28, 2010 at 1:27 AM, kj <no.email at please.post> wrote:

> What's the best to implement assertions in Mathematica?  By assertions
> I mean statements like assert(exp) in C, which generate an error
> if exp evaluates to false.
>
> This *should* be trivial, but it's Mathematica, so...
>
> Naively, I tried defining:
>
> Assert[exp_, msg__] := If[!exp, Message[msg]; Abort[]]
>
> ...which, of course, failed to work (as I've learned to expect);
> instead it produced a cryptic error "Message::name : Message name
> ... is not of the form symbol::name or symbol::name::language."
>
> I tried many other things, but after wasting 1 hour on this
> ridiculously trivial programming task, I'm reduced to begging for
> help.  (This, by the way, is always the way it is with me and
> Mathematica, and I've been using it on-and-off for almost 20 years.
> The documentation is as useless to me today as it was 20 years ago.
> I find it as horrible as the rest of Mathematica is brilliant.)
>
> I've posted desperate questions over programming mind-numbing
> trivialities like this one in Mathematica before, i.e. questions
> that seem so elementary and fundamental that no one who has access
> to the documentation and who can read should *ever* have to ask
> them.  I ask them less wanting to get the answer to the questions
> themselves than hoping to learn how I could have answered such
> questions by myself.  But I've never found how to do this.  Those
> who know the answers *already* can give them to me if they feel so
> inclined.  (And how they got to know the answer to begin with, I
> don't know; I imagine it took years of sustained Mathematica
> programming.  Or maybe they asked a similar question before to
> someone who already knew the answer...)  But no one has been able
> to tell me how someone who *doesn't* know the answers to such questions
> already can figure it out without outside help.
>
> But hope springs eternal!  If someone is kind enough to tell me
> how I could implement my Assert, I'd be most grateful.  If someone
> can tell me how I could have arrived at this answer by myself by
> consulting the documentation, I'd be ecstatic.
>
> TIA,
>
> kj
>
>



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