"Canonicalisation and sorting issues are hardly discussed.

In one place, the fact that a lot of special characters can have
multiple representations is a big argument, while it is not mentioned
how just treating things like a byte sequence would solve this (it
doesn't AFAIU). Like how do you search for $e or $é if you know that
it is possible to represent $é as just $é and as $e + $´ ?"

This, for me, is one of the chief purposes of Unicode support.

What you have it a convertor for "might contain compatibility
codepoints" to "contains only composed sequences of codepoints, and no
compatibility codepoints".  As long as you're not using Strings where
you should use Streams, it should be okay.


And of course, for passing back to ISO Latin 1 or ASCII systems, you
need to have a convertor to "contains only compatibility codepoints,
and no composed sets of codepoints".

As long as you can tell one type from the other, it's not a problem.

Any string that mixes both can be converted in either direction by the
same methods which I've just outlined.

Once you have these, we can do this for all 1 byte characters.

We can then expand this to have Classes and methods for character
strings which contain the occasional character from other ISO
character sets.

Cheers,
    Euan


On 6 December 2015 at 17:44, Sven Van Caekenberghe <sven at stfx.eu> wrote:
>
>> On 05 Dec 2015, at 17:35, Todd Blanchard <tblanchard at mac.com> wrote:
>>
>> would suggest that the only worthwhile encoding is UTF8 - the rest are distractions except for being able to read and convert from other encodings to UTF8. UTF16 is a complete waste of time.
>>
>> Read http://utf8everywhere.org/
>>
>> I have extensive Unicode chops from around 1999 to 2004 and my experience leads me to strongly agree with the views on that site.
>
> Well, I read the page/document/site as well. It was very interesting indeed, thanks for sharing it.
>
> In some sense it made me reconsider my aversion against in-image utf-8 encoding, maybe it could have some value. Absolute storage is more efficient, some processing might also be more efficient, i/o conversions to/from utf-8 become a no-op. What I found nice is the suggestion that most structured parsing (XML, JSON, CSV, STON, ...) could actually ignore the encoding for a large part and just assume its ASCII, which would/could be nice for performance. Also the fact that a lot of strings are (or should be) treated as opaque makes a lot of sense.
>
> What I did not like is that much of argumentation is based on issue in the Windows world, take all that away and the document shrinks in half. I would have liked a bit more fundamental CS arguments.
>
> Canonicalisation and sorting issues are hardly discussed.
>
> In one place, the fact that a lot of special characters can have multiple representations is a big argument, while it is not mentioned how just treating things like a byte sequence would solve this (it doesn't AFAIU). Like how do you search for $e or $é if you know that it is possible to represent $é as just $é and as $e + $´ ?
>
> Sven
>
>> Sent from the road
>>
>> On Dec 5, 2015, at 05:08, stepharo <stepharo at free.fr> wrote:
>>
>>> Hi EuanM
>>>
>>> Le 4/12/15 12:42, EuanM a écrit :
>>>> I'm currently groping my way to seeing how feature-complete our
>>>> Unicode support is.  I am doing this to establish what still needs to
>>>> be done to provide full Unicode support.
>>>
>>> this is great. Thanks for pushing this. I wrote and collected some roadmap (analyses on different topics)
>>> on the pharo github project feel free to add this one there.
>>>>
>>>> This seems to me to be an area where it would be best to write it
>>>> once, and then have the same codebase incorporated into the Smalltalks
>>>> that most share a common ancestry.
>>>>
>>>> I am keen to get: equality-testing for strings; sortability for
>>>> strings which have ligatures and diacritic characters; and correct
>>>> round-tripping of data.
>>> Go!
>>> My suggestion is
>>>    start small
>>>    make steady progress
>>>    write tests
>>>    commit often :)
>>>
>>> Stef
>>>
>>> What is the french phoneBook ordering because this is the first time I hear about it.
>>>>
>>>> Call to action:
>>>> ==========
>>>>
>>>> If you have comments on these proposals - such as "but we already have
>>>> that facility" or "the reason we do not have these facilities is
>>>> because they are dog-slow" - please let me know them.
>>>>
>>>> If you would like to help out, please let me know.
>>>>
>>>> If you have Unicode experience and expertise, and would like to be, or
>>>> would be willing to be, in the  'council of experts' for this project,
>>>> please let me know.
>>>>
>>>> If you have comments or ideas on anything mentioned in this email
>>>>
>>>> In the first instance, the initiative's website will be:
>>>> http://smalltalk.uk.to/unicode.html
>>>>
>>>> I have created a SqueakSource.com project called UnicodeSupport
>>>>
>>>> I want to avoid re-inventing any facilities which already exist.
>>>> Except where they prevent us reaching the goals of:
>>>>   - sortable UTF8 strings
>>>>   - sortable UTF16 strings
>>>>   - equivalence testing of 2 UTF8 strings
>>>>   - equivalence testing of 2 UTF16 strings
>>>>   - round-tripping UTF8 strings through Smalltalk
>>>>   - roundtripping UTF16 strings through Smalltalk.
>>>> As I understand it, we have limited Unicode support atm.
>>>>
>>>> Current state of play
>>>> ===============
>>>> ByteString gets converted to WideString when need is automagically detected.
>>>>
>>>> Is there anything else that currently exists?
>>>>
>>>> Definition of Terms
>>>> ==============
>>>> A quick definition of terms before I go any further:
>>>>
>>>> Standard terms from the Unicode standard
>>>> ===============================
>>>> a compatibility character : an additional encoding of a *normal*
>>>> character, for compatibility and round-trip conversion purposes.  For
>>>> instance, a 1-byte encoding of a Latin character with a diacritic.
>>>>
>>>> Made-up terms
>>>> ============
>>>> a convenience codepoint :  a single codepoint which represents an item
>>>> that is also encoded as a string of codepoints.
>>>>
>>>> (I tend to use the terms compatibility character and compatibility
>>>> codepoint interchangably.  The standard only refers to them as
>>>> compatibility characters.  However, the standard is determined to
>>>> emphasise that characters are abstract and that codepoints are
>>>> concrete.  So I think it is often more useful and productive to think
>>>> of compatibility or convenience codepoints).
>>>>
>>>> a composed character :  a character made up of several codepoints
>>>>
>>>> Unicode encoding explained
>>>> =====================
>>>> A convenience codepoint can therefore be thought of as a code point
>>>> used for a character which also has a composed form.
>>>>
>>>> The way Unicode works is that sometimes you can encode a character in
>>>> one byte, sometimes not.  Sometimes you can encode it in two bytes,
>>>> sometimes not.
>>>>
>>>> You can therefore have a long stream of ASCII which is single-byte
>>>> Unicode.  If there is an occasional Cyrillic or Greek character in the
>>>> stream, it would be represented either by a compatibility character or
>>>> by a multi-byte combination.
>>>>
>>>> Using compatibility characters can prevent proper sorting and
>>>> equivalence testing.
>>>>
>>>> Using "pure" Unicode, ie. "normal encodings", can cause compatibility
>>>> and round-tripping probelms.  Although avoiding them can *also* cause
>>>> compatibility issues and round-tripping problems.
>>>>
>>>> Currently my thinking is:
>>>>
>>>> a Utf8String class
>>>> an Ordered collection, with 1 byte characters as the modal element,
>>>> but short arrays of wider strings where necessary
>>>> a Utf16String class
>>>> an Ordered collection, with 2 byte characters as the modal element,
>>>> but short arrays of wider strings
>>>> beginning with a 2-byte endianness indicator.
>>>>
>>>> Utf8Strings sometimes need to be sortable, and sometimes need to be compatible.
>>>>
>>>> So my thinking is that Utf8String will contain convenience codepoints,
>>>> for round-tripping.  And where there are multiple convenience
>>>> codepoints for a character, that it standardises on one.
>>>>
>>>> And that there is a Utf8SortableString which uses *only* normal characters.
>>>>
>>>> We then need methods to convert between the two.
>>>>
>>>> aUtf8String asUtf8SortableString
>>>>
>>>> and
>>>>
>>>> aUtf8SortableString asUtf8String
>>>>
>>>>
>>>> Sort orders are culture and context dependent - Sweden and Germany
>>>> have different sort orders for the same diacritic-ed characters.  Some
>>>> countries have one order in general usage, and another for specific
>>>> usages, such as phone directories (e.g. UK and France)
>>>>
>>>> Similarly for Utf16 :  Utf16String and Utf16SortableString and
>>>> conversion methods
>>>>
>>>> A list of sorted words would be a SortedCollection, and there could be
>>>> pre-prepared sortBlocks for them, e.g. frPhoneBookOrder, deOrder,
>>>> seOrder, ukOrder, etc
>>>>
>>>> along the lines of
>>>> aListOfWords := SortedCollection sortBlock: deOrder
>>>>
>>>> If a word is either a Utf8SortableString, or a well-formed Utf8String,
>>>> then we can perform equivalence testing on them trivially.
>>>>
>>>> To make sure a Utf8String is well formed, we would need to have a way
>>>> of cleaning up any convenience codepoints which were valid, but which
>>>> were for a character which has multiple equally-valid alternative
>>>> convenience codepoints, and for which the string currently had the
>>>> "wrong" convenience codepoint.  (i.e for any character with valid
>>>> alternative convenience codepoints, we would choose one to be in the
>>>> well-formed Utf8String, and we would need a method for cleaning the
>>>> alternative convenience codepoints out of the string, and replacing
>>>> them with the chosen approved convenience codepoint.
>>>>
>>>> aUtf8String cleanUtf8String
>>>>
>>>> With WideString, a lot of the issues disappear - except
>>>> round-tripping(although I'm sure I have seen something recently about
>>>> 4-byte strings that also have an additional bit.  Which would make
>>>> some Unicode characters 5-bytes long.)
>>>>
>>>>
>>>> (I'm starting to zone out now - if I've overlooked anything - obvious,
>>>> subtle, or somewhere in between, please let me know)
>>>>
>>>> Cheers,
>>>>     Euan
>>>>
>>>>
>>>
>>>
>
>