Re: Creating a coding system

[David Kastrup]

Eli Zaretskii <address@hidden> writes:

>> From: David Kastrup <address@hidden>
>> Cc: address@hidden,  address@hidden
>> Date: Sat, 20 Dec 2014 21:11:49 +0100
>> 
>> > I might be mistaken, but this doesn't look to me like a job for a
>> > coding-system.  You are talking about parsing input into some abstract
>> > notation,
>> 
>> "parsing input" is sort of bombastic for interpreting a binary
>> representation consisting of isolated minimal words.
>
> Yes, but coding-systems machinery is not a general-purpose bytestream
> conversion facility.  It was designed and implemented specifically for
> converting between known families of encodings.  You might be able to
> tweak it enough to do what you want, eventually, but it doesn't look
> like a piece of cake to me.  Programming in CCL is like writing
> assembly code in a restricted machine language, hardly something well
> suited to converting one complex bytestream into another.

Uh, CCL is _exactly_ suited to converting one complex bytestream into
another.  It's overkill for converting regular character set to other
regular character sets which is probably the reason it is phased out.
But for this task it seems a reasonable match.

>> Uh, there is no grammar involved here, no context, most certainly not
>> a push-down stack or something.
>
> But there's definitely some kind of "lexing", no?

No.

> You are talking about sequences of symbols, not about letters from
> some alphabet.

No, Midi contains nothing like symbols.  Just codes with byte or word
sized parameters.  Converting the codes would be straightforward, but
converting the parameters as well would make the tables too large.  CCL
looks like it can come to the rescue for producing Lisp expressions with
the full parameters for _one_ approach.

> If you try representing each sequence as an encoding of a letter,
> won't you get an enormously large alphabet?

Which is exactly why CCL, which can do calculations like divide by 10
with remainder, will be able to save a lot of space if one wants to
arrive at decimal constants in a human-readable rendering of the
parameters.

-- 
David Kastrup