first thank you for using SLY. I'm trying to learn now as well and the documentation/examples are well - less than helpful. (especially after starting with PLY).
So good job!
I'm using your base as a start to port the Monkey Language from go to python - not just straight python but using SLY. Monkey is by Thorsten Ball from his books.
so for this report - the UMINUS parser rule is incorrect - it should be:
@_('"-" expr %prec UMINUS')
def expr(self, p):
return ('neg',p.expr)
you'll have to handle the 'neq' in the interpreter....
again thanks for the this project!