[pure-lang-users] Proposed syntax changes

[Albert G. <Dr....@t-...>]

Hi all,

Now that Pure 0.5 is almost done, I've come to consider some (non 
backward-compatible) syntax changes that I'd like to do, rather now than 
later:

- First and foremost, I want to see whether I can massage the grammar so 
that it becomes possible to write lists of tuples using the special case 
syntax [(1,2),(3,4),...]. That's not straightforward because it 
introduces ambiguities that I'll have to eliminate somehow, but I think 
it's worth the effort, because it sucks having to write 
(1,2):(3,4):...:[] all the time.

- I'd also like to revise the syntax of 'using' so that the module names 
are separated by commas, which is more in line with the 'extern' 
declaration syntax which also uses the comma delimiter. (I'd still like 
to keep the syntax of operator and 'nullary' declarations, though, 
because there whitespace as a delimiter is much easier to read when 
listing non-alphanumeric symbols, IMHO.)

- The discussion I had with Libor about how to implement a sequencing 
operator ("first x, then y") also kept me thinking, because the solution 
I proposed there is not tail-recursive. To do this in a proper way, we'd 
need a built-in sequencing operator (special form). While it's not 
strictly needed, it's much more convenient than having to write 'y when 
_ = x end' all the time.

That sequencing operator should be easy to implement, but how should it 
be named? We can't use Q's '||' because that's logical or in Pure, and 
we can't use C's ',' because that's Pure's tupling operator. Another 
obvious choice would be the Haskell'ish monadic sequencing operator '>>' 
but that's currently used for bit shifts (maybe I could rename '<<'/'>>' 
to shl/shr, though). Any other ideas?

Finally (this is not a syntax change, but it also breaks backward 
compatibility), I'd like to revise the script search. Currently the 
interpreter always searches the current directory and then the PURELIB 
directory. In the case that the interpreter is run with a main script 
(pure -x main.pure), I think it makes sense to search the directory of 
the main script instead of the cwd (for scripts loaded with a 'using' 
clause). That would make it possible to install the main script along 
with any other non-library modules it needs into its own directory and 
run it from there. This would be useful, in particular, for "shebang" 
scripts.

So what do you all think about these? Any objections? Comments?

TIA,
Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag