"not" in variable name doesn't work

When trying this test case:

{ is not exactly 18 : != 18, bob is not exactly 18 : is not exactly 18(16) }.bob is not exactly 18"

the parser fails like this [1]

[1] https://gist.github.com/baldimir/7c13b9c76087d44f95802ded8b72877f

Will provide a PR with a reproducer.