On Feb 4, 2008 11:43 PM, David A. Wheeler <[EMAIL PROTECTED]> wrote:
> Alan Manuel Gloria:
> > However, having a rule about whether it ends up hooking into a macro
> > will then mean having an additional rule that has to be remembered by
> > the user of the new reader, as well as possibly the user of any macro
> > that has to do scanning of that type. So I propose that either the
> > reader completely handles infix, or it completely ignores it - no
> > in-between.
>
> I normally write code so that the macro is never invoked.
You do, but will the end users do too?
>
> > #|Assumes existing functions:
> > (bracketaccess-generic obj &rest dimensions)
> > - accesses a dimensioned object; the number of dimensions
> > given must match the number of dimensions in the actual object
> > (get-number-of-dimensions obj)
> > - determines the number of dimensions in the obj
> > |#
> > (define (bracketaccess o d)
> > (cond
> > ( (listp o)
> > (if (eq (get-number-of-dimensions (car o)) (length o))
> > (apply #'bracketaccess-generic (append o (list d)))
> > (append o (list d)) ))
> > ( (neq 1 (get-number-of-dimensions obj))
> > (list o d) )
> > ( t
> > (bracketaccess-generic o d) )))
> > #|Creating a congruent setf-macro is left as an exercise to the reader|#
> >
> > In the above untested sample, the bracketaccess function never
> > actually "reaches in" the object except at the final bracketaccess
>
> Except that get-number-of-dimensions _does_ need to do a slight reach-in.
> That's because "a[x][y]" in sweet-expressions maps to:
> (bracketaccess (bracketaccess a x) y)
> and so on.
Yes, and that's what the code above handles. If we were to define a
particular get-number-of-dimensions method for arrays:
#|Warning: not sure. I'm a complete CLOS noob. read at your own risk|#
(defmethod (get-number-of-dimensions (a array))
(length (array-dimensions a)) )
So for two-dimensional arrays, array-dimensions returns a list of two
integers, whose length we then measure. This is pretty much all the
reaching-in necessary.
For hash tables we could just have it return a 1:
(defmethod (get-number-of-dimensions (h hash-table))
1)
In fact, for any generic type g (except lists, because we're using
them to hold the curried bracketaccess), we need only to define
methods for get-number-of-dimensions and bracketaccess-generic on g to
be able to handle that type in a nested bracketaccess.
Alternatively we could just switch over to Arc, which I hear is an
automatically currying language ^^.
Sincerely,
AmkG
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