On Feb 20, 2012, at 10:52 AM, Brendan Eich wrote:
> Allen Wirfs-Brock wrote:
> ...
>> Another way to express what I see as the problem with what you are proposing
>> about imposing such string semantics:
>>
>> Could the revised ECMAScript be used to implement a language that had
>> similar but not identical semantic rules to those you are suggested for ES
>> strings. My sense is that if we went down the path you are suggesting, such
>> a implementation would have to use binary data arrays for all of its
>> internal string processing and could not use ES string functions to process
>> them.
>
> If you mean a metacircular evaluator, I don't think so. Can you show a
> counterexample?
>
> If you mean a UTF-transcoder, then yes: binary data / typed arrays are
> required. That's the right answer.
Not necessarily, metacircular...it could be support for any language that
imposes different semantic rules on string elements.
You are essentially saying that a compiler targeting ES for a language X that
includes a string data type that does not confirm to your rules (for example,
by allowing occurrences of surrogate code points within string data) could not
use ES strings as the target representation of its string data type. It also
could not use the built-in ES string functions in the implementation of
language X's built-in functions. It could not leverage any optimizations that
a ES engine may apply to strings and string functions. Also, values of X's
string type can not be directly passed in foreign calls to ES functions. Etc.
Allen
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