[racket] srcloc structures, lists, vectors

I think the other part is historical and an artifact of backwards compatibility.

FWIW, I think the srcloc struct should be transparent or perhaps even
a prefab, which would negate the benefit below.

Robby

On Wed, Sep 14, 2011 at 1:31 PM, Danny Yoo <dyoo at cs.wpi.edu> wrote:
> I wanted to double check my understanding on why source locations have
> several representations in Racket.
>
> One of them is the srcloc structure:
> http://docs.racket-lang.org/reference/exns.html#(def._((lib._racket/private/base..rkt)._srcloc))
>
> But there's also the list and vector representations, all which are
> handled by the syntax/srcloc library in
> http://docs.racket-lang.org/syntax/Source_Locations.html#(def._((lib._syntax/srcloc..rkt)._source-location~3f))
>
> When I first saw the multitude of representations, I was surprised and
> confused: I expected there to be one canonical representation.
>
>
> I made sense of this to myself with the following reasoning: it's
> easier to serialize a vector or list than it is a struct.  In many
> cases, I want to embed source locations somewhere into the output of a
> macro, and it's a lot easier to do something like this:
>
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
> #lang racket
> (define-syntax (where stx)
>  (syntax-case stx ()
>    [(_)
>     (with-syntax ([loc (vector (syntax-source stx)
>                                (syntax-line stx)
>                                (syntax-column stx)
>                                (syntax-position stx)
>                                (syntax-span stx))])
>       #'loc)]))
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>
> than it is to do the equivalent with a srcloc structure:
>
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
> #lang racket
> (define-syntax (where-2 stx)
>  (syntax-case stx ()
>    [(_)
>     (with-syntax ([sloc #`(srcloc '#,(syntax-source stx)
>                                   '#,(syntax-line stx)
>                                   '#,(syntax-column stx)
>                                   '#,(syntax-position stx)
>                                   '#,(syntax-span stx))])
>       #'sloc)]))
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>
> There's several more requirements that the struct approach needs, from
> the use of the module and macro system to be able to bind "srcloc"
> hygienically, to remembering to quote all the internal arguments.  So
> it seems the vector approach is more lightweight.
>
>
> That doesn't quite explain to me why there are both list and vector
> representations for srcloc, though... In any event, it's something
> that's been bothering me, because it's not obvious why there are so
> many representations.
> _________________________________________________
>  For list-related administrative tasks:
>  http://lists.racket-lang.org/listinfo/users
>