join primitive used at type [inf][0] -> [0] crashes REPL

[brianhuffman]

I found this problem while exploring some corner cases of Cryptol's evaluation semantics. For example:

Cryptol> :t join (zero : [inf][0])
join (zero : [inf][0]) : [0]
Cryptol> join (zero : [inf][0])
cryptol: divide by zero

Instead of returning to the REPL prompt, cryptol then exits to the command line.

A related result:

Cryptol> :t join (zero : [inf][0]) == []
(join (zero : [inf][0]) == []) : Bit
Cryptol> join (zero : [inf][0]) == []
cryptol: You have encountered a bug in Cryptol's implementation.
*** Please create an issue at https://github.com/galoisinc/cryptol/issues

%< --------------------------------------------------- 
  Revision:  e48f430b3074c59eec6eec3f9d9fcd1d7bfddfe8
  Branch:    master (non-committed files present during build)
  Location:  [Eval] fromVWord
  Message:   not a word
             compareLeft
%< --------------------------------------------------- 

also:

Cryptol> :prove join (zero : [inf][0]) == []
cryptol: You have encountered a bug in Cryptol's implementation.
*** Please create an issue at https://github.com/galoisinc/cryptol/issues

%< --------------------------------------------------- 
  Revision:  e48f430b3074c59eec6eec3f9d9fcd1d7bfddfe8
  Branch:    master (non-committed files present during build)
  Location:  Cryptol.Symbolic.Prims.cmpValue
  Message:   type mismatch
%< ---------------------------------------------------