[e-lang] Bug: three adjacent colons in printed ENodes

[Kevin Reid]

? e`def a : ::"" := c`
# value: e`def a :::"" := c`

? e`def a :::"" := c`
# syntax error:
#   def a :::"" := c
#          ^

The obvious printed form fails to parse since the lexer is producing  
[::,:] rather than [:,::].

The fix is obvious: arrange for a space or parentheses to be  
inserted. But how should the printer know to do this?

Should an artificial precedence level be introduced?

Should guard-syntax printing look 'down' to see if the guard  
expression will start with ":"?

Should the syntax used for arbitrary nouns be changed?

Should the lexer's interpretation of ":::" be changed?

-- 
Kevin Reid                            <http://homepage.mac.com/kpreid/>