# [NTG-context] MetaPost with Multiple Variable Sections

Wed Sep 18 14:26:34 CEST 2019

```On Wed, 18 Sep 2019, Jeroen wrote:

> \startMPcode
> pair a;
> a := 2cm;

You define a to be a pair and then assign it to a number. Metapost is
telling you that you cannot do that:

>> (xpart a,ypart a)
>> 56.6929
! Equation cannot be performed (pair=numeric).
;
<*> pair a; a := 2cm;
draw fullcircle scaled (2*a); ;
I'm sorry, but I don't know how to make such things equal.
(See the two expressions just above the error message.)

You can fix that by saying

numeric a;
a := 2cm;

One needs to keep in mind that all the code in multiple MPcode
environments are run in the same scope. I occasonally use

\startMPcode
begingroup;
...
endgroup;
\stopMPcode

to avoid interference.