calc.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <SWI-Prolog.h>

int
main(int argc, char **argv)
{ char *expression;
  char *program = argv[0];

  if ( argc < 2 )
  { fprintf(stderr, "Usage: %s expression\n", program);
    exit(1);
  }

  /* Determine length of joined arguments */
  size_t len = 1 + argc - 2;
  for(int n=1; n<argc; n++)
    len += strlen(argv[n]);
  if ( !(expression = malloc(len)) ) // freed on exit
  { perror("allocate");
    exit(1);
  }

  /* combine all the arguments as a single string */
  char *e = expression;
  for(int n=1; n<argc; n++)
  { if ( n != 1 )
      *e++ = ' ';
    strcpy(e, argv[n]);
    e += strlen(e);
  }

  /* make the argument vector for Prolog */

  int   plac=0;
  char *plav[2];
  plav[plac++] = program;
  plav[plac]   = NULL;

  /* initialise Prolog */

  if ( !PL_initialise(plac, plav) )
    PL_halt(1);

  /* Lookup calc/1 and make the arguments and call */

  { predicate_t pred = PL_predicate("calc", 1, "user");
    bool rc;
    term_t h0;

    rc = ( (h0=PL_new_term_refs(1)) &&
	   PL_unify_chars(h0, PL_STRING|REP_MB, (size_t)-1, expression) &&
	   PL_call_predicate(NULL, PL_Q_NORMAL, pred, h0) );

    PL_halt(!rc);
  }

  return 0;
}