[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Minor last-minute issues
Regarding square brackets....
> R6RS imposes this requirement, but R7RS does not.
True, but since treating  as a synonym for () *IS* in R6RS, a large number of Scheme implementations (20!!) implement  as synonyms for (). And since R6RS imposes it, I believe there's a fair amount of code that uses it. I think that many implementations will continue to support  as a synonym for (), in part because of the amount of code that uses it.
> You can't just say "Brackets mean what
> they mean in Scheme", because there is and will be no unified meaning.
By intent, the current draft SRFI-105 spec simply doesn't define unprefixed brackets at all. Different Scheme implementations do different things, as you've already noted. Other Lisps do other things too, for example, Arc has a completely different meaning for [...]. So I believe the spec should *not* impose any particular meaning on unprefixed [...]; there are too many cases where established code requires a particular (but varying) meaning.
If someone wants that to have a specific meaning for unprefixed , I think that should be part of a different spec. I don't think we need to require any particular definition of [...] to meet our goals. Even more importantly, I think trying to force one meaning would greatly *decrease* adoption.
> Since you're providing a full implementation modulo the change to
> the readtable, you need to make some decision for the purposes of that
> implementation, and it's not clear to me what it should be.
The demo implementation implements  as a synonym for (); see the code for underlying-read. I think this is far more widely used meaning, and it makes sense as a demo. But it's not a requirement of the spec; it's just a fact about the demo. (The demo implements basically an R5RS reader plus a few R6RS extras and other extensions, in an effort to make it "useful enough" as a demo.)
The intent is that people would modify their readers to implement SRFI-105, at which point, [...] will do whatever their reader already does.
--- David A. Wheeler