On Tue, 23 Aug 2005, Marcin 'Qrczak' Kowalczyk wrote:
Andre van Tonder <[EMAIL PROTECTED]> writes:
Syntax as lists (or isomorphic to) represents the highest level of
abstraction (on the input) that preserves the meaning of Scheme code.
I would not call lists a higher level of abstraction than
distinguished types for syntax.
What I meant was that you get a higher level of abstraction by ignoring details
(location, comments, etc.) that do not affect the meaning. When you ignore
precisely all these details, you get something that is isomorphic to a list,
every time.
It's not orthogonal. If various instances of the syntax representing 5
are indistinguishable, it's impossible to attach different information
to them.
It would be a pity if the implementation could not report a compile
time warning for (3 4) with source location only because it was passed
through a macro.
As an example of what I mean, invoking syntax-error in the reference
implementation will display the complete backtrace of all intermediate expansion
steps back to the original offending source expression, for which a
source location can be displayed with reader support. While I am not
advocating any particular mechanism now, I personally find this more useful
than just a source location, as some Schemes do, and it is orthogonal to the
syntax-object representation, since nothing needs to be attached to the syntax
data.
Cheers
Andre
