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 => (# # # #
# # # # #
# # # # #
# # # # #
# # # # #
#)

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

Re: Trouble using hashq-get-handle in Guile

[Thien-Thi Nguyen]

() jamil egdemir 
() 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
uncleja...@gmail.com
http://www.power-quant.com
(631) 338-3170 (cell)
-

Re: Trouble using hashq-get-handle in Guile

[Mark H Weaver]

jamil egdemir  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" # # # # #\
 # # # # # #
# # # # #
# # # # # # # # #)

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
uncleja...@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  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