[metapost] test for empty text?

Nicola nvitacolonna at gmail.com
Wed May 29 14:08:11 CEST 2013

In article <005601ce5b9e$be063000$3a129000$@cfraizer.com>,
 Colin Fraizer <metapost at cfraizer.com> wrote:

> Perhaps I am missing something really obvious:
> -          Is there a way to test if the replacement text of a macro is
> empty?

In my experimental library Metappeal 
I have used this hack (the code is in mtpl_lang.mp):

% Vardef: emptytext?
% Returns:
% True if the given text argument consists of no tokens, false otherwise.
vardef emptytext?(text t) =
   mtpl_emptytext? mtpl_aceedabfadfcada1fdb4 t mtpl_aabobfcbadbde759

% Auxiliary macro
vardef mtpl_emptytext?@# text t =
   (str @# = "mtpl_aceedabfadfcada1fdb4mtpl_aabobfcbadbde759")

where those mtpl_* symbols are supposed not to occur anywhere else in 
your program.

Dan's idea seems more elegant, though.


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