[Larceny-users] sqlite3 FFI

[Felix Klock]

On May 31, 2008, at 10:07 AM, Felix Klock wrote:

>
> On May 30, 2008, at 10:56 PM, Peter Keller wrote:
>
>> Hello,
>>
>> I have another question, if I may ask:
>>
>> in my sqlite3 library, I have this:
>>
>>   (define-c-info (include<> "sqlite3.h")
>>     (const SQLITE_INTEGER     int   "SQLITE_INTEGER")
>>     (const SQLITE_FLOAT       int   "SQLITE_FLOAT")
>>     (const SQLITE_BLOB        int   "SQLITE_BLOB")
>>     (const SQLITE_TEXT        int   "SQLITE_TEXT"))
>>
>> and then later something like this:
>>
>>   (define sqlite3-column
>>     (lambda (stmt colid)
>>       (case (sqlite3-column-type stmt colid)
>>         ((SQLITE_INTEGER)
>>           (sqlite3-column-int stmt colid))
>>         ((SQLITE_TEXT)
>>           (sqlite3-column-text stmt colid))
>>         (else
>>           'oops)))) ;; <- obviously this is still test code!
>>
>> It looks like the SQLITE_INTEGER and SQLITE_TEXT in the sqlite3- 
>> column
>> function are not available to me (as the code simply doesn't work and
>> I get 'oops all the time) while in the library codes. If I replace
>> them
>> with the real constants 1 and 3 respectively, or use SQLITE_INTEGER
>> and
>> SQLITE_TEXT in a piece of code which imports the sqlite3 library,  
>> then
>> sqlite3-column behaves properly.
>>
>> Any ideas?
>
> Are you sure you mean to use Scheme's case special form in the above?
>
> That is, is (sqlite3-column-type stmt colid) going to produce a
> Symbol, or an Integer?  If it produces a Symbol, then your case
> expression might work.  If it produces an Integer, then you will never
> get anything other than 'oops back.

One more thing: if you do want to get symbols instead of integers,  
there is another library, foreign-cenums, that is a derivative of the  
foreign-ctools library but provides C enum values as symbols rather  
than integers.

(It does this by internally keeping a table mapping between the  
integers produced by define-c-info and the symbols you provide to the   
define-c-enum or define-c-enum-set special forms.  The code isn't  
anything terribly special and so you may be better off sticking with  
define-c-info, but I thought I should point it out just in case you do  
want to use symbols instead of global variables or integers for the  
SQLITE constants.)

-Felix