presto-main/src/main/java/io/prestosql/type/BooleanOperators.java/BooleanOperators/castToVarchar
class BooleanOperators:    @ScalarOperator(CAST)
    @LiteralParameters("x")
    @SqlType("varchar(x)")
    public static Slice castToVarchar(@SqlType(StandardTypes.BOOLEAN) boolean value)
    {
        return value ? TRUE : FALSE;
    }