On May 7, 2012, at 5:41 PM, Patrick Mahoney wrote:
> #|
> Hello all, in a quest for greater concision, I'm looking for a way to
> abstract over the following code containing mostly definitions. Is there an
> accepted practice for abstraction over definition introduction?|#
>
> (define top-right-x
> (lambda (a-grid-plane a-cell)
>
> ;;The next three definitions are what I am looking to abstract over, as they
> show up in many similarly defined functions.|#
> (match-define (cell row-pos col-pos) a-cell)
>
> (define cell-size (grid-plane->cell-size a-grid-plane))
>
> (match-define (size cell-w cell-h) cell-size)
>
> (+ cell-w
> (* col-pos cell-w))))
>
> (define top-right-y
> (lambda (a-grid-plane a-cell)
>
> (match-define (cell row-pos col-pos) a-cell)
>
> (define cell-size (grid-plane->cell-size a-grid-plane))
>
> (match-define (size cell-w cell-h) cell-size)
>
> (* row-pos cell-w)))
>
> #|How should I approach this? are my options parameters, leaving as is, a
> with- macro?
1. Define a higher-order function that computes these things:
(define (vertical-horizontal body)
(lambda (a-grid-plane a-cell)
... defines ...
(body cell-w col-pos row-pos))) ;; you may need additional parameters
(define top-right-x (vertical-horizontal (lambda (cell-w col-pos row-pos) (+
cell-w (* col-pos cell-w)))
...
That's the best solution.
2. Define a macro for the entire function, not just the three auxiliaries. See
1, but perhaps less notation.
3. If the above is only a hint at how complex your definitions may get, read up
on units. Units are modules abstracted over context, i.e., bundles over
definitions abstracted over other definitions, possibly mutually recursive.
-- Matthias
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