[jerf]

Pattern matching on the "top level branch" of the ADT, whatever you call it, is pretty darned useful.

Pattern matching on the next level down is a power tool to be used with care.

Having used some pattern matching languages for quite some time, I find anything much deeper than that is a code smell at best and pathological at worst. Pattern matching creates coupling proportional to the depth/complexity/precision of the pattern match. The top-level coupling is often unavoidable; if you're pattern matching at all, you certainly care which "branch" you are on and there is likely no refactoring that away. But the danger rises rapidly the deeper in you go. It's just so easy to pattern match on a third-level part of the complex object when you really ought to be wrapping that behind a function somewhere, possibly itself emitting a sum type value.

... but if all you really need is that "top level" match, a lot of pattern matching syntax and features are not really necessary (if not positively dangerous).

[ajross]

> Pattern matching on the "top level branch" of the ADT, whatever you call it, is pretty darned useful. Pattern matching on the next level down is a power tool to be used with care.

Which is exactly how Perl apologia arguments went.