While {:ok, result} | {:error, reason} is ubiquitous, it isn’t always so
strict, and the :ok and :error tuples often deviate in length for added
information, such as Ecto multi results. I think the existing filters work
quite well, so I wouldn’t add it to std lib:
|> Enum.filter(res -> match?(res, {:ok, _}) end)
# or
|> Enum.filter(&match?(&1, {:ok, _}))
Chris
> On Aug 20, 2019, at 10:21 PM, Spencer Carlson <[email protected]>
> wrote:
>
> Given the
>
> {ok, result} | {:error, result}
>
> convention and the beautiful nature of piping, I often find myself looking
> for an elegant way to "strain" out all of the {:error _} results in the
> middle of a pipe so I can continue processing the results that were
> successful. I know the Enum and Stream modules already have a lot of
> functions but I think a strain function would add significant value
> especially in overall code readability.
>
> Here is a possible source example
>
> def strain(enumerable) do
> Enum.reduce(enumerable, [], fn
> {:ok, tuple}, acc when is_tuple(tuple) ->
> case tuple do
> {:ok, result} -> [result | acc]
> {:error, _} -> acc
> end
> {:ok, result}, acc -> [result | acc]
> _, acc -> acc
> end)
> end
>
> And an overloaded version that allows for handling errors:
>
> def strain(enumerable, fun) do
> Enum.reduce(enumerable, [], fn
> {:ok, tuple}, acc when is_tuple(tuple) ->
> case tuple do
> {:ok, result} -> [result | acc]
> {:error, result} ->
> fun.(result)
> acc
> end
> {:ok, result}, acc -> [result | acc]
> {:error, result}, acc ->
> fun.(result)
> acc
> _, acc -> acc
> end)
> end
>
>
> This would allow client code to look like this:
>
> results = list
> |> Enum.map(&do_something/1)
> |> Enum.strain()
> |> Task.async_stream(&do_another_expensive_thing/1)
> |> Enum.strain()
> |> Enum.to_list()
>
>
> Simple examples (for clarity)
> iex> Enum.strain([{:ok, "good job"}, {:error, "bad input"}])
> ["good job"]
>
>
> iex> Enum.strain([{:error, "bad input"}], &IO.inspect/1)
> "bad input"
> []
>
>
> Thanks,
> Spencer Carlson
>
>
>
>
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