diff -u a/ac.scm b/ac.scm --- a/ac.scm 2009-11-21 19:15:40.000000000 -0500 +++ b/ac.scm 2009-11-21 19:23:39.000000000 -0500 @@ -646,11 +646,14 @@ ; default vals with them. To make compatible with existing written tables, ; just use an atom or 3-elt list to keep the default. +(defarc alref arc-alref) + (define (ar-apply fn args) (cond ((procedure? fn) (apply fn args)) ((pair? fn) - (list-ref fn (car args))) + ((if (number? (car args)) list-ref arc-alref) + fn (car args))) ((string? fn) (string-ref fn (car args))) ((hash-table? fn)
In arc3, lists can be called with an integer argument and will return the item in the list at that position:
arc> ('(a b c d e) 2) c
Since calling a list with a non-integer argument results in an error, this means that we could make calling lists with other types do something useful, if we think of something.
I was inspired by thaddeus’ post about adding a syntax to Arc for lookups in association lists to think that perhaps we could have calling a list with a non-integer do an association list lookup.
I often use tables instead of association lists merely because with tables I can use the x!foo notation.
With this patch the x!foo notation will also work for association lists, as long as “foo” is a symbol or something else that isn’t a number.
It doesn’t bother me that
x!2 still returns the item at that position in the list, since when I'm using a table (or now an association list) as an “object”, a container of named values, my keys are symbols anyway.
Taking thaddeus’ example:
arc> (= x '((first "First Name")(last "Last Name"))) ((first "First Name") (last "Last Name"))
arc> x!first "First Name"
arc> x!last "Last Name"
Note that this patch doesn’t implement setting values in an association list. I.e.,
(= alist!foo 3)
Download alistcall0.patch and its prerequisite: defarc.
Or, using the hackinator:
hack ycombinator.com/arc/arc3.1.tar \ awwx.ws/defarc0.patch \ awwx.ws/alistcall0.patch
This patch is in the public domain. The combination of this patch and Arc may be redistributed or modified under the same terms as Arc itself.