Assignment to Assignment operators does not work

[mmatera]

Description

When I try to overload the assignment operator for a certain kind of expression, a warning message is shown.

How to Reproduce

mathics -e '(F[x_] := s_) ^:= Q[x, s]' -e 'F[1]:=2'

Output Given

UpSetDelayed::write: Tag Pattern in F[x_] := s_ is Protected.
None

Q[1,2]

Expected behavior

The warning message should not be there:

None

Q[1,2]

Your Environment

Mathics 7.0.1dev0
on CPython 3.8.12 (heads/pyston_main:759470647d, Apr 1 2022, 15:36:47)
using SymPy 1.13.3, mpmath 1.3.0, numpy 1.21.4, cython 0.29.25

Workarounds

Surround the first assignment with Quiet

Priority

Low: It just produces a warning, but it should not be there, meaning that we are handling something wrong with the assignment code, or with pattern matching.

Additional context

Overload the assignment operator is used in some WL packages, like CellsToTeX. Also, I want to mimic the formatting algorithm in WMA using WL