test47 assignment bug

[LunaStev]

I initially suspected the bug in test47 was related to assignment parsing and tried to fix the parse_assignment function, but it turns out the issue lies elsewhere.
The error message Error: Expected primary expression, found Equal indicates that Wave's variable handling may be the actual cause.

In Wave, var is used for mutable variables and let for constants. However, in test47, the following lines:

a = 12;
b = 5;

seem to fail because a and b are used without prior declaration.

I believe the current variable system does not properly handle implicit declarations or assignments to undeclared identifiers. This might be causing the parser to misinterpret the = as a primary expression error.

I'll now investigate the variable tracking or declaration logic instead.