GLR backend reaches unreachable code

[abiggerhammer]

Gary Berger reports that the following example, using the Python bindings, either segfaults or fails an assert with "unknown HCFChoice type":

import hammer as h

digit = h.ch_range('0', '9')
upper = h.ch_range('A', 'Z')
lower = h.ch_range('a', 'z')
chars = h.choice(digit, upper, lower)

chars.compile(h._PB_GLR)

Reproduces on OS X Sierra. The LL(k) and LALR backends have not exhibited this behavior yet. (I tried with Gary's example.)

[pesco]

Meredith L. Patterson on Tue, Jun 27 2017:

```import hammer as h digit = h.ch_range('0', '9') upper = h.ch_range('A', 'Z') lower = h.ch_range('a', 'z') chars = h.choice(digit, upper, lower) chars.compile(h._PB_GLR)``` Reproduces on OS X Sierra. The LL(k) and LALR backends have not exhibited this behavior yet. (I tried with Gary's example.)

Is this specific to the Python binding or does it happen from C also?

[abiggerhammer]

I haven't checked yet (this landed while I was prepping a talk) but I can look this afternoon.

[abiggerhammer]

In preliminary investigation I'm not able to reproduce this without the Python bindings. I'll also try some of the other bindings that use SWIG, to see if I can narrow down the problem.