implement access_file/2 in C

C/iopreds.c

@@ -2332,6 +2332,75 @@ p_access(void)
   }
 }
 
+static Int
+p_access2(void)
+{
+  Term tname = Deref(ARG1);
+  Term tmode = Deref(ARG2);
+  char ares[YAP_FILENAME_MAX];
+  Atom atmode;
+
+  if (IsVarTerm(tmode)) {
+    Yap_Error(INSTANTIATION_ERROR, tmode, "access");
+    return FALSE;
+  } else if (!IsAtomTerm (tmode)) {
+    Yap_Error(TYPE_ERROR_ATOM, tname, "access");
+    return FALSE;
+  }
+  atmode = AtomOfTerm(tmode);
+  if (IsVarTerm(tname)) {
+    Yap_Error(INSTANTIATION_ERROR, tname, "access");
+    return FALSE;
+  } else if (!IsAtomTerm (tname)) {
+    Yap_Error(TYPE_ERROR_ATOM, tname, "access");
+    return FALSE;
+  } else {
+    if (atmode == AtomNone)
+      return TRUE;
+    if (!Yap_TrueFileName (RepAtom(AtomOfTerm(tname))->StrOfAE, ares, (atmode == AtomCsult)))
+      return FALSE;
+  }
+#if HAVE_ACCESS
+  {
+    int mode;
+
+    if (atmode == AtomExist)
+      mode = F_OK;
+    else if (atmode == AtomWrite)
+      mode = W_OK;
+    else if (atmode == AtomRead)
+      mode = R_OK;
+    else if (atmode == AtomAppend)
+      mode = W_OK;
+    else if (atmode == AtomCsult)
+      mode = R_OK;
+    else if (atmode == AtomExecute)
+      mode = X_OK;
+    else {
+      Yap_Error(DOMAIN_ERROR_IO_MODE, tmode, "access_file/2");
+      return FALSE;   
+    }
+    if (access(ares, mode) != 0) {
+      /* ignore errors while checking a file */
+      return FALSE;
+    }
+    return TRUE;
+  }
+#elif HAVE_STAT
+  {
+    struct SYSTEM_STAT ss;
+
+    if (SYSTEM_STAT(ares, &ss) != 0) {
+    /* ignore errors while checking a file */
+      return FALSE;
+    }
+    return TRUE;
+  }
+#else
+  return FALSE;
+#endif
+}
+
 static Int
 p_exists_directory(void)
 {
@@ -6455,6 +6524,7 @@ Yap_InitIOPreds(void)
   Yap_InitCPred ("get0", 2, p_get0, SafePredFlag|SyncPredFlag|HiddenPredFlag);
   Yap_InitCPred ("$get0_line_codes", 2, p_get0_line_codes, SafePredFlag|SyncPredFlag|HiddenPredFlag);
   Yap_InitCPred ("$get_byte", 2, p_get_byte, SafePredFlag|SyncPredFlag|HiddenPredFlag);
+  Yap_InitCPred ("access_file", 2, p_access2, SafePredFlag|HiddenPredFlag);
   Yap_InitCPred ("$access", 1, p_access, SafePredFlag|SyncPredFlag|HiddenPredFlag);
   Yap_InitCPred ("exists_directory", 1, p_exists_directory, SafePredFlag|SyncPredFlag);
   Yap_InitCPred ("$open", 6, p_open, SafePredFlag|SyncPredFlag|HiddenPredFlag);