Re: [Reduce-algebra-developers] rerror question (fwd)

[Rainer S. <rai...@gm...>]

Two remarks:

1. I suspect that the calls to rerror were intended as a start point for a more 
specific error management. E.g., by passing an error number and a module name, 
Reduce would be able display a corresponding help document. This is a good idea, 
but we would need to (a) convert everything to that scheme and (b) write 
documentation for the errors - which would be a Good Thing anyway.

2. There is a way to use symbolic error names. If you write

put('listerr,'newnam,1);

you instruct the parser to replace _every_ occurence of the token listerr by the 
token 1. Consequently, you can write

 rerror('nlopt, listerr, {"list of size", n, "expected!"});

You have to be careful to use identifiers that are not used elsewhere, so 
 
  !E!R!R!O!R!-list!-expected

would be a better (and more easily understandable) identifier.

  Rainer 



On Fri, 24 Oct 2014 at 08:21 +0100, Arthur Norman wrote:

 > I am replying to this via the general list first in case it is useful to 
 > anybody else and secondly because an attempt at a direct response saw my 
 > email bounced, so I hope this is a way to get through.
 > 
 > On Thu, 23 Oct 2014, Kostas Oikonomou wrote:
 > > Is it possible to define a "constant" in your module and use it as an
 > > error number in 'rerror(...)'?
 > > 'rerror' seems to require a literal integer.  Managing error numbers by
 > > literal integers is difficult.
 > > So I'd like to be able to say smth. like
 > > listerr := 1
 > > ...
 > > if not listp(bounds) or length(bounds) neq n+1 then
 > >     rerror('nlopt, listerr, {"list of size", n, "expected!"});
 > > But doing this results in
 > > ***** liberr invalid as RERROR argument
 > > Thanks.
 > >                        Kostas
 > 
 > The effect you observe arises in formrerror in rlisp/form.red which is 
 > imposing constraints on the arguments to rerror and permitting us without a 
 > quote of arg1.
 > 
 > symbolic procedure formrerror(u,vars,mode);
 >     begin scalar x;
 >        argnochk u;
 >        if not fixp caddr u then typerr(caddr u,"RERROR argument");
 >        x := formc!*(cadddr u,vars,mode);
 >        if idp cadr u then return list('rerror,mkquote cadr u,caddr u,x)
 >         else if eqcar(cadr u,'quote) and idp cadadr u
 >          then return list('rerror,cadr u,caddr u,x)
 >         else typerr(cadr u,"RERROR argument")
 >     end;
 > 
 > so that indeed explicitly insists on a literal numeric argument.
 > 
 > If you look in rlisp/lpri.red you see
 > 
 > symbolic procedure rerror(packagename,number,message);
 >     progn(errmsg!* := message, rederr message);
 > 
 > and rerror discards/ignores its first two arguments, so there is to my mind 
 > little huge purpose of using it rather then just calling rederr directly!
 > 
 > Arthur
 > 
 > 
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   Rainer Schöpf