[q-lang-users] [cowan: Chicken Scheme to Q interface almost ready for beta]

[John C. <co...@cc...>]

I'm really, really close to releasing the beta version of my egg for
Chicken Scheme, which provides Chicken programmers with convenient access
to the Q interpreter.  There are only four points left:

1) Some code has not yet been fully tested.

2) I have to write some HTML documentation.

2) Improper tuples like "(1,2|3)" aren't yet being converted from
S-expressions to Q binary representation.  I expect they will be rare in
Q expressions as opposed to rules: there is no S-expression representation
of rules.

3) There is a conflict of expectations between Scheme and Q programmers
around applications with multiple arguments.  The Q application "f x"
is written in S-expression form as (q:call f x); the "q:call" symbol
marks it as an application rather than a list.  (There are good reasons
for not using a quote on the Scheme side.)

Since Q is currying but Scheme is not, I allow "f x y" to be written as
(q:call f x y) on the Scheme side, and that is treated as if it were
(q:call (q:call f x) y).  In particular, (q:call + 1 2) will properly
reduce to 3.

The difficulty arises when a binary operation is given more than two
arguments.  While testing, I tried normalizing (q:call + 1 2 3) and got
back the surprising result (q:call 3 3).  At first I thought there was
a bug, but then I realized that the equivalent form was (q:call (q:call
(q:call + 1) 2) 3), or in Q notation "(+) 1 2 3", which in fact means
"((+) 1 2) 3" or simply "(1 + 2) 3", which indeed reduces to "3 3".

Nevertheless, this *is* surprising, and means that to represent "1+2+3"
as an S-expression one must write nested q:call lists.  I thought of
treating applications where the second element is an operator specially,
but that would make it impossible to write the equivalent of "(1 + 2) 3"
should one wish to do so.

I'm very much open to suggestions on this one.  Should I leave
things alone?  Should I introduce another q:xxx flag to mark calls of
binary operators (required only if there are more than two arguments)?
Or something else?  If the last, what?

-- 
But the next day there came no dawn,            John Cowan
and the Grey Company passed on into the         co...@cc...
darkness of the Storm of Mordor and were        http://www.ccil.org/~cowan
lost to mortal sight; but the Dead
followed them.          --"The Passing of the Grey Company"