[metapost] Processing comma separated values

[Aditya Mahajan]

On Fri, 26 Feb 2010, Nicola wrote:

> In article <alpine.LNX.2.01.1002261133470.25584 at ybpnyubfg.ybpnyqbznva>,
> Aditya Mahajan <adityam at umich.edu> wrote:
>
>> On Fri, 26 Feb 2010, Taco Hoekwater wrote:
>> 
>> > Aditya Mahajan wrote:
>> >> What is the canonical way of processing a list of comma separated values 
>> >> in 
>> >> metapost.
>
> A similar problem is dealt with in Appendix D of The METAFONTbook. The
> “dirty trick” in your case (working only for pairs) becomes:
>
> def boxsep(suffix A)(text T) =
>   -A.e forsuffixes B = T : + B.w = -B.e endfor + (whatever,whatever)
> enddef;
>
> having noticed that
>
> b.w - a.e = c.w - b.e = d.w - c.e
>
> can be re-written as
>
> -a.e + b.w = -b.e + c.w = -c.e + d.w

Ah! All this while I was thinking how to get the first two arguments.

> Another possibility is the following:
>
> def boxsep(text T) =
>   (whatever,whatever)
>   forsuffixes B = T : + B.w = -B.e endfor
>   + (whatever,whatever)
> enddef;
>
> which has the advantage of permitting for loops in the argument, e.g., 
> you may write:
>
> boxsep(a0 for i = 1 upto 100: ,a[i] endfor) = p;
>
> instead of
>
> boxsep(a0, a1, a2, ..., a100) = p;

Thanks. This may be useful in the future.

Is the METAFONTbook the only source to learn such tricks?

Aditya