Trouble using hashq-get-handle in Guile

Trouble using hashq-get-handle in Guile

[jamil egdemir]

Hi Everyone,

I'm having trouble getting the value associated with a key in a
hash-table and I'm totally confused as to what I'm doing wrong.  The
code I'm using is shown below:

    (use-modules (curl))
    (use-modules (json))

    ;; use curl to hit the site's api to get results of query as json:
    (define handle (curl-easy-init))
    (curl-easy-setopt handle 'url

"http://api.data.gov:80/regulations/v3/documents.json?api_key=mySecKey&countsOnly=0&encoded=1&dktid=EPA-HQ-OAR-2013-0602&dkt=R&cp=C&rpp=25&po=0")
    (define s (curl-easy-perform handle))

    ;; parse the json in the string into guile scheme:
    (define queryResults (json-string->scm s))

    ;; use this to see the keys and values in the resulting hash
table:
    (define print-hash (lambda (my-hash)
                         (hash-for-each (lambda (key value)
                                          (format #t "~a => ~a~%" key value))
                                        my-hash)))

    ;; now let's take a look at the keys and values:
    (print-hash queryResults)

    ;; now let's get the value associated with the documents key:
    (hashq-get-handle queryResults 'documents)

It relies on [guile-curl][1] and [guile-json][2] to talk to the
webserver and to parse the response.  Things seem pretty
straight-forward until I run.  I can see the response from the server
in json (very long and not posted here) and from within Emacs (using
geiser to poke around) I can see:

    scheme@(guile-user)> (hash-table? queryResults)
    $25 = #t

so I know that queryResults is indeed a hash-table.  When I take a
look at the keys and associated values using print-hash I see that:

    scheme@(guile-user)> (print-hash queryResults)
    totalNumRecords => 23318
    documents => (#<hash-table 2ad7c60 17/31> #<hash-table 2afdbc0
17/31> #<hash-table 2b0ab60 17/31> #<hash-table 2b0eb00 17/31>
#<hash-table 2b10aa0 17/31> #<hash-table 2b13a40 17/31> #<hash-table
2b189e0 17/31> #<hash-table 2b1b980 17/31> #<hash-table 2b1e920 17/31>
#<hash-table 2b228c0 17/31> #<hash-table 2b25860 17/31> #<hash-table
2b29800 17/31> #<hash-table 2b2d7a0 17/31> #<hash-table 2b30740 17/31>
#<hash-table 2b336e0 17/31> #<hash-table 2b38680 17/31> #<hash-table
2b3b620 17/31> #<hash-table 2b3f5c0 17/31> #<hash-table 2b44560 17/31>
#<hash-table 2b48500 17/31> #<hash-table 2b4c4a0 17/31> #<hash-table
2b50440 17/31> #<hash-table 2b533e0 17/31> #<hash-table 2b57380 17/31>
#<hash-table 2b5c320 17/31>)

so that's good and it's what I expected.  But when I try to use
hashq-get-handle to get a look at the value for totalNumRecords or
documents I get:

    scheme@(guile-user)> (hashq-get-handle queryResults 'totalNumRecords)
    $24 = #f

    scheme@(guile-user)> (hashq-get-handle queryResults 'documents)
    $24 = #f

which seems to indicate the key doesn't exist in the hash-table
queryResults.  I've tried all night with quotes, w/o quotes, futzing
with the SRFI-69 hash-table implementations (during which I discovered
the difference between native guile hash-tables and the SRFI-69
hash-tables), and went through the [hash table examples][3] in the
guile reference manual (they all worked just fine).  I'm out of ideas.

If someone could help me understand why my calls to hashq-get-handle
aren't working out as expected I'd be most grateful.

BTW, this question is also posted at:

http://stackoverflow.com/questions/27348357/trouble-using-hashq-get-handle-in-guile

Thanks for the help in advance.

  [1]: http://www.lonelycactus.com/guile-curl.html
  [2]: https://github.com/aconchillo/guile-json
  [3]: http://www.gnu.org/software/guile/manual/html_node/Hash-Table-Examples.html#Hash-Table-Examples

-j
-- 
-------------------------------------------------------------
Jamil Egdemir
unclejamil@gmail.com
http://www.power-quant.com
(631) 338-3170 (cell)
-------------------------------------------------------------

Re: Trouble using hashq-get-handle in Guile

[Thien-Thi Nguyen]

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() jamil egdemir <unclejamil@gmail.com>
() Sun, 7 Dec 2014 17:44:46 -0500

       (hashq-get-handle queryResults 'documents)

IIUC, the hash table object ‘queryResults’ is made by:

 https://github.com/aconchillo/guile-json/blob/master/json/parser.scm

proc ‘read-object’.  For interop w/ the ‘make-hash-table’ it calls, you
might try some variants of ‘hashq-get-handle’, namely ‘hash-get-handle’
or ‘hashv-get-handle’.

-- 
Thien-Thi Nguyen
   GPG key: 4C807502
   (if you're human and you know it)
      read my lisp: (responsep (questions 'technical)
                               (not (via 'mailing-list)))
                     => nil

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Re: Trouble using hashq-get-handle in Guile

[jamil egdemir]

Thien-Thi,

> IIUC, the hash table object ‘queryResults’ is made by:
>
>  https://github.com/aconchillo/guile-json/blob/master/json/parser.scm
>
> proc ‘read-object’.  For interop w/ the ‘make-hash-table’ it calls, you
> might try some variants of ‘hashq-get-handle’, namely ‘hash-get-handle’
> or ‘hashv-get-handle’.

Thank you for the suggestion.  I tried both hash-get-handle and
hashv-get-handle:

scheme@(guile-user)> (hash-get-handle queryResults 'totalNumRecords)
$27 = #f
scheme@(guile-user)> (hashv-get-handle queryResults 'totalNumRecords)
$28 = #f

seems like the result is the same. No love.  Good suggestion though...

-j



-- 
-------------------------------------------------------------
Jamil Egdemir
unclejamil@gmail.com
http://www.power-quant.com
(631) 338-3170 (cell)
-------------------------------------------------------------

Re: Trouble using hashq-get-handle in Guile

[Mark H Weaver]

jamil egdemir <unclejamil@gmail.com> writes:

> I'm having trouble getting the value associated with a key in a
> hash-table and I'm totally confused as to what I'm doing wrong.  The
> code I'm using is shown below:
>
>     (use-modules (curl))
>     (use-modules (json))
>
>     ;; use curl to hit the site's api to get results of query as json:
>     (define handle (curl-easy-init))
>     (curl-easy-setopt handle 'url
>
> "http://api.data.gov:80/regulations/v3/documents.json?api_key=mySecKey&countsOnly=0&encoded=1&dktid=EPA-HQ-OAR-2013-0602&dkt=R&cp=C&rpp=25&po=0")
>     (define s (curl-easy-perform handle))
>
>     ;; parse the json in the string into guile scheme:
>     (define queryResults (json-string->scm s))
>
>     ;; use this to see the keys and values in the resulting hash
> table:
>     (define print-hash (lambda (my-hash)
>                          (hash-for-each (lambda (key value)
>                                           (format #t "~a => ~a~%" key value))
>                                         my-hash)))
>
>     ;; now let's take a look at the keys and values:
>     (print-hash queryResults)
>
>     ;; now let's get the value associated with the documents key:
>     (hashq-get-handle queryResults 'documents)

Based on a quick glance at the json code, I suspect you want this:

  (hash-get-handle queryResults "documents")

i.e. change 'hashq-get-handle' to 'hash-get-handle', and pass a string
as the key, not a symbol.

If you use "~s" instead of "~a" in 'print-hash', it will be clear
whether the keys are strings or symbols because strings will print
within double quotes.

     Regards,
       Mark

Re: Trouble using hashq-get-handle in Guile

[jamil egdemir]

Mark,

> Based on a quick glance at the json code, I suspect you want this:
>
>   (hash-get-handle queryResults "documents")
>
> i.e. change 'hashq-get-handle' to 'hash-get-handle', and pass a string
> as the key, not a symbol.

BOOM!

scheme@(guile-user)> (hash-get-handle queryResults "documents")
$29 = ("documents" #<hash-table 297f820 17/31> #<hash-table 2982700
17/31> #<hash-table 29896a0 17/31> #<hash-table 298f640 17/31> #\
<hash-table 29915e0 17/31> #<hash-table 299d580 17/31> #<hash-table
29a1520 17/31> #<hash-table 29a34c0 17/31> #<hash-table 29a6460 \
17/31> #<hash-table 29f7400 17/31> #<hash-table 29fd3a0 17/31>
#<hash-table 2a08340 17/31> #<hash-table 2a1c2e0 17/31> #<hash-table \
2a4b280 17/31> #<hash-table 2a96220 17/31> #<hash-table 2aa31c0 17/31>
#<hash-table 2aa5160 17/31> #<hash-table 2aaa100 17/31> #<has\
h-table 2ab10a0 17/31> #<hash-table 2abb040 17/31> #<hash-table
2accfe0 17/31> #<hash-table 2acef80 17/31> #<hash-table 2ad1f20 17/3\
1> #<hash-table 2af1ec0 17/31> #<hash-table 2af4e60 17/31>)

All good now.

> If you use "~s" instead of "~a" in 'print-hash', it will be clear
> whether the keys are strings or symbols because strings will print
> within double quotes.

Excellent suggestion. I'll do that. Thanks to both you and ttn!

-j
-- 
-------------------------------------------------------------
Jamil Egdemir
unclejamil@gmail.com
http://www.power-quant.com
(631) 338-3170 (cell)
-------------------------------------------------------------

Re: Trouble using hashq-get-handle in Guile

[Mike Gran]

On Sunday, December 7, 2014 4:49 PM, jamil egdemir <unclejamil@gmail.com> wrote:
 >Mark,
>
>> Based on a quick glance at the json code, I suspect you want this:
>>
>>   (hash-get-handle queryResults "documents")
>>
>> i.e. change 'hashq-get-handle' to 'hash-get-handle', and pass a string
>> as the key, not a symbol.
>
>BOOM!


As an aside, guile 2+ has native functions for fetching via plain HTTP.
You shouldn't have to utilize guile-curl unless your query requires
special handling: https for example.

-Mike