public PrologElement readClause() {
reset_var_number();
PrologElement clausa, left, right;
boolean marseille_if = false;
String dir_name;
if (symbol_control == 1) {
clausa = readElement();
if (clausa == null) return null;
return readRightSide(clausa, false);
}
if (symbol_control == 11 && root.if_atom_caption.equals(symbol)) {
marseille_if = true;
get_symbol();
}
switch (symbol_control) {
case 22:
get_symbol();
if (symbol_control != 11) {
root.message("Syntax error (directory expected).");
return null;
}
dir_name = "";
get_symbol();
if (symbol_control != 21) {
root.message("Syntax error (atom after dot expected).");
return null;
}
get_symbol();
left = root.atom(dir_name, symbol);
if (left == null) {
root.message("Unknown atom: " + symbol);
return null;
}
break;
case 11:
left = atomC(symbol);
if (left == null) return null;
break;
default:
return null;
}
get_symbol();
switch (symbol_control) {
case 6:
right = root.earth();
get_symbol();
break;
case 1:
right = readElement();
if (right == null) return null;
right = readRightSide(right, false);
if (right == null) return null;
get_symbol();
break;
default:
right = root.earth();
break;
}
clausa = root.pair(root.pair(left, right), root.earth());
if (symbol_control == 21) return clausa;
if (symbol_control != 11
|| (!root.if_atom_caption.equals(symbol) && !marseille_if)
|| (marseille_if && !root.and_atom_caption.equals(symbol))) return null;
PrologElement el = clausa;
while (symbol_control != 21) {
left = readElement();
if (left == null) return null;
get_symbol();
switch (symbol_control) {
case 6:
right = root.earth();
get_symbol();
el.setRight(root.pair(root.pair(left, right), root.earth()));
break;
case 1:
right = readElement();
if (right == null) return null;
right = readRightSide(right, false);
if (right == null) return null;
get_symbol();
el.setRight(root.pair(root.pair(left, right), root.earth()));
break;
default:
if (left.isAtom()) el.setRight(root.pair(root.pair(left, root.earth()), root.earth()));
else el.setRight(root.pair(left, root.earth()));
break;
}
el = el.getRight();
if (symbol_control != 21
&& symbol_control != 23
&& (symbol_control != 11 || !root.and_atom_caption.equals(symbol))) return null;
}
return clausa;
}
public PrologElement readRightSide(PrologElement LEFT, boolean secondary) {
PrologElement left, right;
get_symbol();
if (root.separator_caption.length() > 0) {
switch (symbol_control) {
case 1:
left = readElement();
if (left == null) return null;
left = readRightSide(left, false);
if (left == null) return null;
LEFT = root.pair(LEFT, left);
get_symbol();
break;
case 6:
LEFT = root.pair(LEFT, root.earth());
get_symbol();
break;
default:
break;
}
}
switch (symbol_control) {
case 52:
if (secondary) return root.pair(LEFT, root.earth());
root.message("Syntax error (bracket mismatch).");
return null;
case 2:
if (!secondary) return root.pair(LEFT, root.earth());
root.message("Syntax error (bracket mismatch).");
return null;
case 3:
right = readElement();
if (right == null) return null;
if (right.isEarth()) {
root.message("Syntax error (earth not allowed here).");
return null;
}
get_symbol();
if ((symbol_control != 2 && !secondary) || (symbol_control != 52 && secondary)) {
root.message("Syntax error (closing bracket expected).");
return null;
}
return root.pair(LEFT, right);
default:
break;
}
if (root.separator_caption.length() > 0) {
if (symbol_control == 23) get_symbol();
else {
root.message("Syntax error (separator expected).");
return null;
}
}
switch (symbol_control) {
case 11:
left = atomC(symbol);
if (left == null) root.message("Unknown atom: " + symbol);
break;
case 22:
get_symbol();
if (symbol_control != 11) {
root.message("Syntax error (directory expected).");
return null;
}
String dir_name = "" + symbol;
get_symbol();
if (symbol_control != 21) {
root.message("Syntax error (atom after dot expected).");
return null;
}
get_symbol();
left = root.atom(dir_name, symbol);
if (left == null) root.message("Unknown atom: " + symbol);
break;
case 10:
left = root.integer(int_symbol);
break;
case 56:
case 6:
left = root.earth();
break;
case 5:
left = root.slash();
break;
case 4:
left = root.fail();
break;
case 7:
left = root.var(get_var_number(symbol));
break;
case 8:
left = root.text(symbol);
break;
case 18:
left = root.Double(double_symbol);
break;
case 51:
left = readElement();
if (left == null) return null;
right = readRightSide(left, true);
if (right == null) return null;
left = right;
break;
case 1:
left = readElement();
if (left == null) return null;
left = readRightSide(left, false);
if (left == null) return null;
break;
case 21:
left = atomC(symbol);
if (left == null) root.message("Dot atom does not exist.");
break;
default:
return null;
}
if (left == null) return null;
left = readRightSide(left, secondary);
if (left == null) return null;
return root.pair(LEFT, left);
}