[NTG-context] question about vardef variables
taco at bittext.nl
Mon Jan 18 09:13:10 CET 2021
> On 17 Jan 2021, at 11:17, Damien Thiriet <damien at thiriet.web4me.fr> wrote:
> I have some troubles with understanding metafun's macro mechanism.
> Given this MWE:
> vardef Test (expr ab,cd)=
> %numeric ab;
> %numeric cd;
> draw unitsquare scaled 10 xshifted ab;
> draw unitsquare scaled 10 yshifted cd;
> Test (50,100);
> Uncommenting the two declarations makes me run intro a silent error. I was
> lucky enough yesterday to get an explicit error message with a more
> complex macro. It made me figure out where my problems came from.
> So here are my two questions:
> - Why shouldn't we tell metafun if expr is a path, a pair or so on?
You were (attempting to) redefine the macro’s arguments, but they are read-only.
A somewhat longer answer: the type of macro arguments in this case is “expr”.
Metapost argument types are based solely on what the internal language parser
needs to interpret the code; the language is not strongly typed.
Also, during macro expansion, your code is replaced by:
%numeric (READONLY TEMP VALUE 1);
%numeric (READONLY TEMP VALUE 2);
draw unitsquare scaled 10 xshifted (READONLY TEMP VALUE 1);
draw unitsquare scaled 10 yshifted (READONLY TEMP VALUE 2);
Taco Hoekwater E: taco at bittext.nl
genderfluid (all pronouns)
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