Unicode alternative for '..' (ticket #3894)

[Yitzchak Gale]

My opinion is that we should either use TWO DOT LEADER,
or just leave it as it is now, two FULL STOP characters.

Two dots indicating a range is not the same symbol
as a three dot ellipsis.

Traditional non-Unicode Haskell will continue to be
around for a long time to come. It would be very
confusing to have two different visual glyphs for
this symbol.

I don't think there is any semantic problem with using
TWO DOT LEADER here. All three of the characters
ONE DOT LEADER, TWO DOT LEADER, and HORIZONTAL
ELLIPSIS are legacy characters from Xerox's XCCS.
There, the characters they come from were used for forming
dot leaders, e.g., in a table of contents. Using them that way
in Unicode is considered incorrect unless they represent text
that was originally encoded in XCCS; in Unicode, one does
not form dot leaders using those characters. However, other
new uses are considered legitimate. For example, HORIZONTAL
ELLIPSIS can be used for fonts that have a special ellipsis glyph,
and ONE DOT LEADER represents mijaket in Armenian encodings.
So I don't see any reason why we can't use TWO DOT LEADER to
represent the two-dot range symbol.

The above analysis is based in part upon a discussion of these
characters on the Unicode list in 2003:

http://www.mail-archive.com/unicode@unicode.org/msg16285.html

The author of that particular message, Kenneth Whistler, is
of the opinion that two dots expressing a range as in [0..1]
should be represented in Unicode as two FULL STOP characters,
as we do now in Haskell. Others in that thread - whom
Mr. Whistler seems to feel are less expert than himself
regarding Unicode - think that TWO DOT LEADER is appropriate.
No one considers replacing two-dot ranges with HORIZONTAL
ELLIPSIS.

If we can't find a Unicode character that everyone agrees upon,
I also don't see any problem with leaving it as two FULL STOP
characters.

Thanks,
Yitz