On Tue, May 03, 2005 at 09:22:11PM +0100, Nicholas Clark wrote:
>
> Whilst I confess that it's unlikely to be me here, if anyone has the time
> to contribute some help, do you have a list of useful self-contained tasks
> that people might be able to take on?
Actually, overnight I realized there's a relatively good-sized
project that needs figuring out -- identifying character properties
such as isalpha, islower, isprint, etc. Here I'll briefly sketch
how I'd like it to work, and maybe someone enterprising can take
things from there for us.
Currently Parrot offers quite a few ops for character properties --
namely "is_whitespace", "is_wordchar", "is_digit", etc. and their
"find_XXX" counterparts. While these are useful, the set is also
incomplete -- at the moment I haven't found anything that let's
us find alphabetic, uppercase, lowercase, etc. properties. (If I've
just overlooked something, please point it out!)
I suppose Parrot could add a bunch of new "is_alpha", "is_upper",
"is_lower", etc. ops, but having separate opcodes for every
property actually complicates the design of PGE a fair bit
as well as makes a lot of very function-specific opcodes.
What would *really* be useful would be to have three basic opcodes:
is_cclass(out INT, in INT, in STR, in INT)
Set $1 to 1 if the codepoint of $3 at position $4 is in
the character class(es) given by $2.
find_cclass(out INT, in INT, in STR, in INT, in INT)
Set $1 to the offset of the first codepoint matching
the character class(es) given by $2 in string $3, starting
at offset $4 for up to $5 codepoints. If no matching
character is found, set $1 to -1.
find_not_cclass(out INT, in INT, in STR, in INT, in INT)
Set $1 to the offset of the first codepoint not matching
the character class(es) given by $2 in string $3, starting
at offset $4 for up to $5 codepoints. If the substring
consists entirely of matching characters, set $1 to -1.
The character classes in $2 above are given by an integer bitmask,
defined according to the following table (or something like it --
I took this table from ctype.h on my system, then added a "newline"
class):
0x0001 - uppercase char
0x0002 - lowercase char
0x0004 - alphabetic char
0x0008 - numeric character
0x0010 - hexadecimal digit
0x0020 - whitespace
0x0040 - printing
0x0080 - graphical
0x0100 - blank (i.e., SPC and TAB)
0x0200 - control character
0x0400 - punctuation character
0x0800 - alphanumeric character
0x1000 - newline character
We have 32 bits available, so we could extend this table as needed.
And EVENTUALLY we'll probably need a more general interface
to handle Unicode properties as well as character class compositions,
but I speculate that we can do those either in a library, or
(if speed is needed) we can build a "character class" PMC type
optimized for charsets and have:
is_cclass(out INT, in PMC, in STR, in INT)
find_cclass(out INT, in PMC, in STR, in INT, in INT)
find_not_cclass(out INT, in PMC, in STR, in INT, in INT)
But for now the integer representation of character classes
ought to be sufficient.
Anyway, that's another very useful self-contained task that
I'd be glad to have a volunteer for.
Pm
