[R6RS] Unicode normalization
mflatt at cs.utah.edu
Thu Mar 2 13:04:05 EST 2006
After experimenting with Unicode normalization and re-reading the SRFI
discussion, I propose the following simple change to the SRFI:
* Add `string-normzlize-nfd',
Each of these procedures takes a string and return its D, KD, C, or
KC normalization, respectively.
Originally, I imagined just picking one. But the one I would have
picked is NFC, and but the time you have NFC, it's a small step to have
all four. Also, all of them are useful to programs that deal with
Unicode somewhat explicitly.
I recommend against using any normalization for symbols or input
streams. Here's my rationale:
* Normalizing symbols without normalizing strings will lead to
confusion, since 'ê (that's a quote followed by U+00EA) would not
be the same as (string->symbol "ê") with NFD or NFKD
normalization. If NFC or NFKC is used, adjust the example by
decomposing ê to two characters in the string.
* For consistency overall, normalization needs to be pushed down to
the lexical level. Otherwise, #\ê might turn out to be the ê
character, or it might be a syntax error (i.e., a #\e followed by
anon-delimiting character). In other words, we'd have to either
require a program to be represented as a normalize stream of
characters, or specify normalization as part of the parsing
* Normalizing things like strings probably interferes with
representing literal data in strings. For example, I would guess
that pathnames like "ê" typically use NFC-like encodings, but I'm
By not specifying normalization, however, we push the problem into
programming environments and editors. If a programmer types an "ê", for
example, the specific meaning will depend on how the editor saves the
program text. So, I'm not sure it's the right approach.
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