> On Oct 18, 2017, at 12:53 AM, Konrad Hinsen <konrad.hin...@fastmail.net>
> wrote:
>
> I needed to remove the first
> element and add it in front of the others. On a plain list, I could do
> this half asleep. But with the list wrapped in a syntax object, even
> after considerable thought I am not sure what the best approach would
> be.
>
> Unwrap (syntax->datum), apply list functions, rewrap? The resulting code
> is not very readable, the wrapping stuff being much more visible than
> the code that does the real work. Pattern match against (a b c ...)? OK
> for this particular case, but not for the next case I knew I would
> have to deal with.
The fandango associated with switching between syntaxed lists and lists of
syntax can indeed be wearying. But this seems less like an issue intrinsic to
`syntax-parse` and more like the irreducible complexity of living in a world
where syntax objects are distinct things. (See also strings vs. paths and
strings vs. symbols).
If your goal is readable code, why not add some sugar?
#lang racket/base
(require (prefix-in rb: racket/base)
rackunit)
(define (length x)
(cond
[(and (syntax? x) (syntax->list x)) => length]
[else (rb:length x)]))
(check-equal? (length '(1 2 3)) 3)
(check-equal? (length #'(1 2 3)) 3)
(check-exn exn:fail:contract? (λ () (length 42)))
(check-exn exn:fail:contract? (λ () (length #'42)))
More broadly, it feels like there's plenty of room for new macro-definition and
syntax-processing forms that suit different ergonomic needs: readability,
automatic error messages, debugging, and so on. Interesting question why more
of them don't exist. For `#lang br` I made a set that were designed for
simplicity and readability. [1]
[1]
http://docs.racket-lang.org/br/index.html?q=br%2Fdefine#%28form._%28%28lib._br%2Fdefine..rkt%29._define-macro%29%29
<http://docs.racket-lang.org/br/index.html?q=br/define#(form._((lib._br/define..rkt)._define-macro))>
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