Re: Accessing PowerLoom from Haskell

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On 08/31/2015 06:16 AM, Anders N=E5sell wrote:
> Den 2015-08-28 19:31, Hans Chalupsky skrev:
>> ... There could be some problems with all the C++ constructor initiali=
zation code being run when your C or Haskell program starts up, but that =
should be solvable.
> I saw in the PowerLoom Manual "6.2.1.6 CLOS Objects versus Structs" tha=
t it is possible to get an API with
> structs instead of CLOS objects. Would this be a way to get some OO out=
 of the API?
>
> If so I suppose a tool like e.g. http://www.swig.org/ could then be use=
d to generate the C API?
>
> Anders
Anders,

I just tested it and the C++ initialization code is called just fine=20
when linked into a C program.  I thought it would, I just wasn't=20
completely sure.  I don't think there is a good reason to get OO into=20
the C API.  Almost all of the PLI functions are functions, and the very=20
few methods can be wrapped via functions (they are only used for PLI=20
Iterators, I think).  There is no need to access the slots of any=20
objects directly, if it turns out that there is, we should add accessors=20
for them in the API.  Objects can be passed around by their pointers=20
which in C simply have to be declared as void*.  I didn't know about=20
SWIG which looks interesting but seems overkill for this.

Below is a a working example on how to call PowerLoom from C.  In the=20
longer term, the PLI C entry points should be generated automatically by=20
the STELLA translator (which won't involve much code) and we'll have a C=20
include file that you can use to get access to the API in C.  For now,=20
you just have to write that yourself for the PLI functions you want to us=
e.

I am attaching three little source files which you can compile and run=20
like this (provided you have built the PowerLoom C++ version once to get=20
access to the compiled libraries):

% setenv PL_HOME .../powerloom-4.x.y
% g++ -I$PL_HOME/native/cpp=20
-I$PL_HOME/native/cpp/stella/cpp-lib/gc/include -c pli-c-api.cc=20
-DSTELLA_USE_GC
% gcc -c powerloom-from-c.c
% gcc pli-c-api.o powerloom-from-c.o -o powerloom-from-c=20
-L$PL_HOME/native/cpp/lib -lpowerloom -lpowerloom-extensions -lutilities=20
-llogic -lstella -lgc -lm -lstdc++
% setenv LD_LIBRARY_PATH $PL_HOME/native/cpp/lib
% ./powerloom-from-c
Initializing...
(defconcept person)
/PL-KERNEL-KB/PL-USER/PERSON
(defrelation friend-of (?x ?y)))
FRIEND-OF
(assert (and (person fred) (person susi))))
((PERSON FRED) (PERSON SUSI))
(assert (friend-of fred susi))
(FRIEND-OF FRED SUSI)
(retrieve all (person ?x))
[2015-SEP-02 13:24:04.000 PL] Processing check-types agenda...
(SUSI FRED)

(retrieve all (friend-of ?x ?y))
((FRED SUSI))


Hans


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void pli_initialize();
void* pli_s_evaluate(char* command, char* moduleName);
char* pli_s_evaluate_to_string(char* command, char* moduleName);
char* pli_object_to_string(void* object);
void* pli_s_change_module(char* name);

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// g++ compilation:   g++ -o globals globals.cc

// Compile like this:
// setenv PL_HOME /tmp/build-kagg
// % g++ -I$PL_HOME/native/cpp -I$PL_HOME/native/cpp/stella/cpp-lib/gc/include -c pli-c-api.cc -DSTELLA_USE_GC

#include "powerloom/powerloom-system.hh"

namespace pli {
  using namespace stella;
  using namespace logic;

extern "C" void pli_initialize() {
  initialize();
}

extern "C" void* pli_s_evaluate(char* command, char* moduleName) {
  return sEvaluate(command, moduleName, NULL);
}

extern "C" char* pli_s_evaluate_to_string(char* command, char* moduleName) {
  Object* result;
  result = sEvaluate(command, moduleName, NULL);
  if (result != NULL)
    return objectToString(result);
  else
    return (char*) ""; // for simplicity
}

extern "C" char* pli_object_to_string(Object* object) {
  if (object != NULL)
    return objectToString(object);
  else
    return NULL;
}

extern "C" void* pli_s_change_module(char* name) {
  return sChangeModule(name, NULL);
}

}

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// Compile and run like this:
//
// % setenv PL_HOME .../powerloom-4.x.y
//
// % g++ -I$PL_HOME/native/cpp -I$PL_HOME/native/cpp/stella/cpp-lib/gc/include -c pli-c-api.cc -DSTELLA_USE_GC
// % gcc -c powerloom-from-c.c
// % gcc pli-c-api.o powerloom-from-c.o -o powerloom-from-c -L$PL_HOME/native/cpp/lib -lpowerloom -lpowerloom-extensions -lutilities -llogic -lstella -lgc -lm -lstdc++
// % setenv LD_LIBRARY_PATH $PL_HOME/native/cpp/lib
// % ./powerloom-from-c
/*
Initializing...
(defconcept person)
/PL-KERNEL-KB/PL-USER/PERSON
(defrelation friend-of (?x ?y)))
FRIEND-OF
(assert (and (person fred) (person susi))))
((PERSON FRED) (PERSON SUSI))
(assert (friend-of fred susi))
(FRIEND-OF FRED SUSI)
(retrieve all (person ?x))
[2015-SEP-02 13:24:04.000 PL] Processing check-types agenda...
(SUSI FRED)

(retrieve all (friend-of ?x ?y))
((FRED SUSI))

*/


#include "pli-c-api.h"
#include <stdio.h>

main ()
{
  char* command;
  char* module="PL-USER";

  printf("Initializing...\n");
  pli_initialize();

  printf("%s\n", command = "(defconcept person)");
  printf("%s\n", pli_s_evaluate_to_string(command, module));

  // change module for nicer result printing:
  pli_s_change_module(module);

  printf("%s\n", command = "(defrelation friend-of (?x ?y)))");
  printf("%s\n", pli_s_evaluate_to_string(command, module));

  printf("%s\n", command = "(assert (and (person fred) (person susi))))");
  printf("%s\n", pli_s_evaluate_to_string(command, module));

  printf("%s\n", command = "(assert (friend-of fred susi))");
  printf("%s\n", pli_s_evaluate_to_string(command, module));

  printf("%s\n", command = "(retrieve all (person ?x))");
  printf("%s\n", pli_s_evaluate_to_string(command, module));

  // passing objects:
  command = "(retrieve all (friend-of ?x ?y))";
  void* result = pli_s_evaluate(command, module);
  printf("%s\n", command);
  printf("%s\n", pli_object_to_string(result));
}

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