package luan.impl;

import luan.Luan;
import luan.LuanFunction;
import luan.LuanException;
import luan.LuanElement;
import luan.LuanTable;


// unary minus
final class UnmExpr extends UnaryOpExpr {

	UnmExpr(LuanElement el,Expr op) {
		super(el,op);
	}

	@Override public Object eval(LuanStateImpl luan) throws LuanException {
		Object o = op.eval(luan);
		if( o instanceof Number )
			return -((Number)o).doubleValue();
		luan.push(el,null);
		try {
			if( o instanceof LuanTable ) {
				LuanFunction fn = luan.getHandlerFunction("__unm",(LuanTable)o);
				if( fn != null ) {
					return Luan.first(fn.call(luan,new Object[]{o}));
				}
			}
			throw luan.exception("attempt to perform arithmetic on a "+Luan.type(o)+" value");
		} finally {
			luan.pop();
		}
	}
}