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I'm pretty sure the answer is "no", especially in some reasonable way. If `Result` was defined in some object-oriented way, i.e. as an interface with `Ok` and `Error` being implementations of that interface, or if this was O'Caml and `Result` had been defined as a polymorphic variant, then you could do this. That said, the openness of these approaches would be inappropriate for `Result`.

Defined as a discriminated union, you can't accomplish this. However, the "right" way to handle this, which is roughly equivalent to the above approaches, but with explicit rather than implicit conversions, is not to put the strings into the `Result` type in the first place. Or, in your case, avoid boolean blindness, a term popularized (and coined?) in [this blog post](https://existentialtype.wordpress.com/2011/03/15/boolean-blindness/), but search engines will return many other more recent discussions.

Instead of discovering which case of the `Result` you have with the pattern match in `filterError` and then immediately discarding that type information by returning a `bool`, you could instead have a function `fromError : Result<'a, 'e> -> Option<'e>`, this maintains the type information. Your `filterError` function would then become `Seq.collect (fromError >> Option.toList)`.

If we adapt to the new type of `filterError`, then applying the same aversion to discarding type information to `mergeErrors` would lead to it simply being the identity function.

In general, uses of `bool` should be considered skeptically, and you should see if a `bool`-producing function can be replaced with a function that gives evidence for the result it returns. Functions like `Seq.isEmpty`, `Option.isSome`, `Option.isNone`, `Result.isError`, `Result.isOk`, etc. are almost never what you want. They and booleans in general tend to lead to implicit contracts between parts of your code. That this contract is implicit is part of the "blindness" of boolean blindness. Replacing `bool` returning functions with `Option` or `Choice` returning functions is often a solution.