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Re: SRFI 105: Curly-infix-expressions
> Draft 7 isn't yet published, but soon will be. Draft 6 is the current
> published draft.
Whups, of course I meant draft 6.
> R6RS says that `equal?` "returns #t if and only if the (possibly
> infinite) unfoldings of its arguments into regular trees are equal as
> ordered trees." I sort of know what that means, but it isn't the kind
> of thing I'd like to put into a standard. We have a window in the next
> few days to get better language into draft 7, if you have any on tap.
I have several concerns about cycle-detection in R7RS, which I think is otherwise shaping up pretty nicely. Trying to deal with equal? led me to realize some weirdnesses with equal?, write, and display. I'll see what I can do quickly.
> It's not obvious to me why you want to bother with this. No Scheme I
> know of behaves well in the presence of cycles *in code*, and indeed
> R7RS prohibits them explicitly. I know that curly-expressions can be
> used outside of code, but I expect (and I think you expect too) that
> code will be their dominant use.
True. But since it will be used to read data, my concern was protecting the reader.
> I think it's a win to support `equal?`, with or without cycle detection.
Okay, fair enough.
> > > R6RS #!-switch is the closest I can think of that can make a source
> > > file self-descriptive about the lexical syntax it uses. Did you
> > > think about using something like #!c-expr ?
> > A switch might work, though I think the #! syntax for switches is
> > absurd; the #! sequence is ALREADY reserved by most Unix/Linux
> > systems, and they will not change it for Scheme :-(.
> Only as the first two characters of a file. Putting a blank line before
> a Scheme-specific switch will defeat the Unix interpretation
Fair enough. But will *Scheme* ignore it properly when it IS the first character of a file? Guile, clisp, and many other Lisps will ignore #!...!# so that you can create Scripts in Scheme / Common Lisp / whatever. That is really useful functionality, and one that I hate to interfere with.
> (which, by
> the way, is not part of Posix, though quite pervasive in everything but
Yes, I know. But the POSIX authors' rejection of #! has not exactly prevented its implementation :-). I use #! all the time. There's no reason Schemes can't support it, it makes scripting far more pleasurable.
> I think the SRFI should prescribe the switch (say, #!srfi-105),
> since there is no reason why it should be different on different
Okay, adding a switch seems to be strongly advocated, and I'm certainly amenable. Any preference on the switch name?:
--- David A. Wheeler