Waiting for someone else to comment, I propose this

<assign|rightChoice|<\macro|x>
  <math-table-base|<left|.><tformat|<cwith|1|-1|1|-1|cell-swell|<value|table-math-swell>>|<arg|x>><right|}>>

  \;
</macro>>

I started from the macro that defines choice (that I got from the "Edit macro" menu command) and I moved both the brace from left to right and the point from right to left. I do not master yet the editing of macros in the TeXmacs source mode, but it worked and it gives what you want as far as I can tell. Let me know if you need step by step instructions to make it work.

G.

Am 10.01.2021 um 16:56 schrieb Vincent Douce Mathoscope:

bonjour

two TeXmacs users ask me how to make right l'accolade } , thus the symétric of \choice

i mean not only typing } but having this :

x=1|

   |->x+y=3

y=2|

with a large vertical } instead of the |->

----

Vincent Douce

https://lemathoscope.com/

cours de maths postbac par visio