[metapost] Metapost doesn't like `z01' for point names

[Rodolfo Medina]

On Sun, 17 Jun 2007, Rodolfo Medina wrote:

>> Please excuse the basic question.
>> If I name a point `z01' Metapost complains:
>>
>> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>> %file test.mp
>> beginfig(1);
>>
>> z0 = (0,0);
>> z1 = (1,1);
>>
>> z01 = 0.5[z0,z1];
>>
>> endfig;
>>
>> end
>> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>>
>> $ mpost test
>> This is MetaPost, Version 0.641 (Web2C 7.4.5)
>> (test.mp
>> ! Inconsistent equation (off by -0.5).
>> <to be read again>
>>                    ;
>> l.8 z01 = 0.5[z0,z1];
>>
>> ?
>>
>>
>> Instead, if I name it `z11' it's okay.  Why?  I really would like to name it
>> `z01': is it definitely impossible?



Hartmut Henkel <hartmut_henkel at gmx.de> writes:

> z01 == z1 == z[1] == e. g. z0001.0 due to MetaPost's token rules, see e.
> g. MFBook p. 50. And z1 was defined already. Numeric suffixes even
> include the decimal point, another example: z.0100 == z.01 == z[0.01].



I worked it out this way:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
beginfig(1);
u=2cm;

pair p[]; pair p[]_[];

p0 = (0,0) * u;
p1 = (1,1) * u;

p0_1 = 0.5[p0,p1];

draw p0..p0_1..p1;

endfig;

end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


; instead, if I simply put `z' in place of `p', it fails:


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
beginfig(1);
u=2cm;

pair z[]; pair z[]_[];

z0 = (0,0) * u;
z1 = (1,1) * u;

z0_1 = 0.5[z0,z1];

draw z0..z0_1..z1;

endfig;

end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

$ mpost test
This is MetaPost, Version 0.641 (Web2C 7.4.5)
(test.mp
! Declared variable conflicts with previous vardef.
<to be read again>
                   ;
l.5 pair z[];
              pair z[]_[];
?


I can't understand: so there are some letters which are forbidden to be
used that way?  Can anyone provide some explanation?

Thanks,
Rodolfo