Simplified error checking while I was at it, too.

The `original_pattern` introduced a tenuous dependency to the expression
value as a whole, and after some consideration, I decided that it would
be better for the developer to manage their own pattern strings.

In the event you need to print the text representation of a pattern,
it's usually better that you manage the memory of it as well.

This should hopefully avoid any issues with loading operands greater
than 8 bits on alignment-sensitive platforms.

We don't directly support printing these.

To prevent future issues being raised about the pattern being missing if
someone tries to print one, hide everything.