[metapost] [graph.mp] bug in gdata?
mailing_list at arcor.de
Sat Mar 3 21:46:40 CET 2007
[Full quote, because this mail wasn't copied to the list.]
Ryan Van Wagoner schrieb:
> Hi Stephen,
> in graph.mp, gdata is implemented as:
> def gdata(expr f)(suffix $)(text c) =
> for i=1 upto infinity:
> exitunless Grdln_$(f);
> It appears that `i' is a loop variable in the context that your text
> parameter is evaluated in, and therefore should not be assigned to.
Why use i at all here? What about
forever: exitunless ... ?
> Does anyone know if there is a way to create unique or non-referencable
> parameters to prevent these collisions from happening (similar to
> `gensym' in common lisp or the concept of hygenic macros in Scheme)?
> Maybe the loop variable in gdata should be called `i_' as seems to be
> the convention that Knuth suggests in "The Metafont Book" for variables
> internal to a format or input program.
Would be a much better idea if forever can't be used there, since i is
such a common index name. It took me ages to find this out, because I
knew I did something similar already. With another substitute name
>>>>>> "Stephen Hennig" == Stephan Hennig <mailing_list at arcor.de> writes:
> Stephen Hennig> Hi,
> Stephen Hennig> in the following file manipulating a variable j or (any?) other variable
> Stephen Hennig> inside gdata (from graph.mp) works fine. Except for variable i. That
> Stephen Hennig> variable throws and error in MetaPost v0.901. A bug?
> Stephen Hennig> Best regards,
> Stephen Hennig> Stephan Hennig
> Stephen Hennig> input graph
> Stephen Hennig> beginfig(1);
> Stephen Hennig> numeric i, j;
> Stephen Hennig> j := 0;
> Stephen Hennig> gdata("test.dat", v, j:=j+1; );%%% Works.
> Stephen Hennig> % i := 0;
> Stephen Hennig> % gdata("test.dat", v, i:=i+1; );%%% Fails.
> Stephen Hennig> endfig;
> Stephen Hennig> end
> Stephen Hennig> Instead of "test.dat" you can take any file name of a text file, e.g.,
> Stephen Hennig> the MetaPost source file name itself.
> Stephen Hennig> _______________________________________________
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> Stephen Hennig> http://tug.org/mailman/listinfo/metapost
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