[e-lang] Guard-based pattern expansions

[Mark S. Miller]

If we keep via but use the just-proposed syntax to make via and guard patterns 
not seem similar, we could also stop allowing guards on list patterns. Of the 
expansions previously listed as non-problematic, the only one that would need 
to change is:


> '[p0, ..., pn_1] + r'  to  '[p0, ..., pn_1, r] :__SplitList[n]'
would instead expand to
          'via (__splitList(n)) =~ [p0, ..., pn_1, r]'


If we get rid of guarded list patterns, guards would only be able to guard 
variable definitions and the ignore pattern ("_"). I think this will interact 
well with Zooko's auditing proposal, which I will explain shortly.

-- 
Text by me above is hereby placed in the public domain

     Cheers,
     --MarkM