[racket] idioms for abstracting over definitions

Thank you all, you have given me much to think on here. I had versions that
used a generic function as suggested, but I wasn't sure if the cognitive
overhead in understanding the generic strategy outweighed the benefits to
concision. I think it probably does in some cases, probably related to how
difficult it is to develop a good name for the generic function. However,
in this case, I'm on board. Thank you for your time.

-Patrick

On 8 May 2012 09:23, Matthias Felleisen <matthias at ccs.neu.edu> wrote:

>
>
> 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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