/1. It may be used together with PL_chars_to_term(), but the typical use case will create a number of clauses for the same predicate. The fastest way to achieve this is by creating a term that represents the invariable structure of the desired clauses using variables for the variable sub terms. Now we can loop over the data, binding the variables, asserting the term and undoing the bindings. Below is an example loading words from a file that contains a word per line.

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

#define MAXWLEN 256

static foreign_t
load_words(term_t name)
{ char *fn;

  if ( PL_get_file_name(name, &fn, PL_FILE_READ) )
  { FILE *fd = fopen(fn, "r");
    char word[MAXWLEN];
    module_t m = PL_new_module(PL_new_atom("words"));
    term_t cl = PL_new_term_ref();
    term_t w  = PL_new_term_ref();
    fid_t fid;

    if ( !PL_unify_term(cl, PL_FUNCTOR_CHARS, "word", 1, PL_TERM, w) )
      return FALSE;

    if ( (fid = PL_open_foreign_frame()) )
    { while(fgets(word, sizeof word, fd))
      { size_t len;

        if ( (len=strlen(word)) )
        { word[len-1] = '\0';
          if ( !PL_unify_chars(w, PL_ATOM|REP_MB, (size_t)-1, word) ||
               !PL_assert(cl, m, 0) )
            return FALSE;
          PL_rewind_foreign_frame(fid);
        }
      }

      PL_close_foreign_frame(fid);
    }

    fclose(fd);
    return TRUE;
  }

  return FALSE;
}

install_t
install(void)
{ PL_register_foreign("load_words", 1, load_words, 0);
}

12.4.17.4 Getting file names

The function PL_get_file_name() provides access to Prolog filenames and its file-search mechanism described with absolute_file_name/3. Its existence is motivated to realise a uniform interface to deal with file properties, sea