Re: [Chicken-users] Why does the JSON egg map JSON structs to Scheme vectors instead of alists?

[Daishi Kato]

Even though I agree that it should be schemish,
it must be consistent.

How would you deal with
{"1":[2,3],"4":[5,6]}
and
[["1",2,3],["4",5,6]]
that must be distinguished?

Furthermore, if we were to change the spec of the json egg,
we should be aware with backward compatibility issues.
Otherwise, I need to change my all json-related code.

Best,
Daishi

At Sun, 27 Nov 2011 14:16:38 +0100,
Vok Vojwo wrote:
> 
> I am a bit confused by the way the JSON egg maps JSON structures to
> Scheme values. The JSON egg maps a structure to a vector:
> 
> (use json)
> (with-input-from-string "{\"pi\":3.14,\"e\":2.71}" json-read)
> ;; => #(("pi" . 3.14) ("e" . 2.71))
> 
> This makes it impossible to use the standard Scheme function assoc to
> read the data.
> 
> The following functions fix the problem:
> 
> (define (json->alist arg)
>   (cond
>    ((vector? arg)
>     (map (lambda (pair)
>            (cons (car pair) (json->alist (cdr pair))))
>          (vector->list arg)))
>    ((list? arg)
>     (list->vector (map json->alist arg)))
>    (else arg)))
> 
> (define (alist->json arg)
>   (cond
>    ((list? arg)
>     (list->vector (map (lambda (pair)
>                          (cons (car pair) (alist->json (cdr pair))))
>                        arg)))
>    ((vector? arg)
>     (map alist->json (vector->list arg)))
>    (else arg)))
> 
> A small verification test:
> 
> (use http-client)
> 
> (define (with-input-from-url url chunk)
>   (with-input-from-request url #f chunk))
> 
> (define json
>   (with-input-from-url
>    "http://www.google.com/calendar/feeds/address@hidden/public/full?alt=json";
>    json-read))
> 
> (equal? json (alist->json (json->alist json)))
> ;; => #t
> 
> By using alists it is possible to use assoc to access the data:
> 
> (define (assoc* alist . path)
>   (let assoc* ((path path)
>                (alist alist))
>     (if (null? path)
>         alist
>         (assoc* (cdr path)
>                 (cdr (assoc (car path) alist))))))
> 
> (assoc* (json->alist json) "feed" "title" "$t")
> ;; => "Official Google External Developer Events"
> 
> Is there any reason why the JSON egg creates vectors of pairs?
> 
> If not I would suggest to fix it to make it more schemish.
> 
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