Re: Loading database from string (C API)

Hello again,

On Wed, Dec 11, 2013 at 03:59:09PM +0100, Jan Wielemaker wrote:
> On 12/11/2013 03:41 PM, Edd Barrett wrote:
>
> Search for blob.  Basically, if PL_term_type() gives PL_ATOM, it
> may be a blob or a real atom.  Use PL_is_atom() to find out.
> 

With this workaround applied I am now at the point where I am calling
load_files/2, as suggested earlier in this thread. Sadly something
is amiss; ideally I would have a C program to demonstrate, but this
would be a fairly large piece of code and I would have to translate it
from Python CFFI to C. Before I go there let's see if anything obvious
springs out.

So I have constructed the predicate and arguments needed to call
load_files(pl_source, [stream(pl_stream)]), where pl_source is an atom to
identify the code in the stream (as described in the docs) and pl_stream is
the stream opened using the open_stream C function that we have already
discussed. For testing purposes I have passed the theory "f(1)." to the
function.

The call to load_files/2 (in Python/CFFI) looks like this:
pl_qid = self.libpl.PL_open_query(self.ffi.NULL, self.libpl.PL_CATCH_Q_CATCH_EXCEPTION, pl_pred, pl_args)

pl_pred is a the result of a PL_predicate() call for load_files of arity
2. pl_args is an 'array'(?) of term refs as given by PL_new_term_refs().
To check these are good I can call PL_get_chars with CVT_WRITE_CANONICAL:

Arg 1: swithon_theory -- arbitrary name chosen for the stream
Arg 2: '.'(stream(<stream>(0x18ebfd824c00)),[]) -- list with one element, the stream

Looks OK. The qid returned looks valid too. The call to open_query is
followed by: pl_sol = self.libpl.PL_next_solution(pl_qid);

At this point we use PL_exception() to check for an exception etc.

The problem is execution never gets past the call to PL_next_solution.
The interpreter seems to be stuck in a loop printing:

---8<---
ERROR: Syntax error: Unexpected end of clause
ERROR:  
ERROR: ** here **
ERROR: . 
ERROR: Syntax error: Unexpected end of clause
ERROR:  
ERROR: ** here **
ERROR: . 
ERROR: Syntax error: Unexpected end of clause
...
---8<---

Stuff I have tried:
 * Remove dot on the end of the theory string -- same error.
 * Varying the theory string in other ways -- no change.
 * Try different PL_Q_* -- no difference.
 * Change character encoding on the stream -- same.

Is that expected behaviour?

-- 
Best Regards
Edd Barrett

http://www.theunixzoo.co.uk