Hi Matt, thanks for the proposal.
My concern with the proposal is that it introduces yet another way of
pattern matching, compared to case, =, and match?. Imagine I wrote this
code:
case res do
{:ok, value} -> value
:error -> :default
end
And if someone in a code review asked me to rewrite this code, I am not
sure how pleased I would be. I see the following issues:
1. By not declaring the other cases, we are implicitly discarding them. A
case would at least require an explicit `_ ->`
2. By defaulting to `nil` for unmatched cases, we introduce more scenarios
where nil can creep into the code. For example, your first example would
raise an error on nil if the string does not match
3. If for some reason I need to extract two variables from the same
pattern, I need to rewrite the code or extract it twice (duplication,
inefficient)
Plus, pattern_filter seems to be designed for piping, which makes sense,
but in Elixir the pattern is (almost?) always on the left side of the value.
PS: I didn't reply exactly because I was waiting to see if the proposal
developed in different ways. Typically speaking, if there wasn't an
explicit "go ahead", then it won't be accepted unless it is further
developed. :)
On Thu, Dec 15, 2022 at 10:31 PM 'Matt Farabaugh' via elixir-lang-core <
elixir-lang-core@googlegroups.com> wrote:
> Hi Ben,
>
>
>
> I agree that it reduces its applicability, but I see that as a virtue.
> Filter and Map are useful despite being less applicable than Reduce, since
> they are simpler.
>
>
>
> Matt F
>
>
>
> *From: *<elixir-lang-core@googlegroups.com> on behalf of Ben Wilson <
> benwilson...@gmail.com>
> *Reply-To: *"elixir-lang-core@googlegroups.com" <
> elixir-lang-core@googlegroups.com>
> *Date: *Thursday, December 15, 2022 at 4:23 PM
> *To: *elixir-lang-core <elixir-lang-core@googlegroups.com>
> *Subject: *Re: [EXTERNAL] Re: [elixir-core:11221] [proposal] Use patterns
> to filter data (good for pipes)
>
>
>
> This email came from a source outside of CoverMyMeds. Use caution when
> clicking on links or replying with confidential information.
> ------------------------------
>
> Apologies, I missed that you addressed how `{1, 2, 3} |>
> pattern_filter({1, a, b})` would work in your earlier reply, in that you
> only allow a single variable to be bound. This further reduces its general
> applicability.
>
> On Thursday, December 15, 2022 at 4:12:37 PM UTC-5 Ben Wilson wrote:
>
> Hi Matt,
>
>
>
> I am not on the core team nor do I speak for them. From what I have
> generally seen, "alternative APIs" that can be implemented as libraries
> generally should just stay libraries, unless there develops a strong
> following that makes it clear that such an API should be moved into the
> core.
>
>
>
> Tangentially, is this code available anywhere?
>
>
>
> As for my take on this proposal, I don't really agree with your responses
> to `then`.
>
>
>
> > The additional typing involved for the anonymous function distracts the
> reader from the pattern matching, which is the crux of the matter.
>
>
>
> 50% of the additional typing is related to specifying the return shape,
> and in this respect that typing is well worth it, because there's no guess
> work. Code is read far more often than written, and the implicit return
> structure of `pattern_filter` leaves me guessing about how it works in
> cases like this:
>
>
>
> ```
>
> {1, 2, 3} |> pattern_filter({1, a, b})
>
> #=> ?
>
> ```
>
>
>
> `then` is mildly more verbose, but it composes clearly with functions
> without requiring macro magic:
>
>
>
> # assertive success
>
> iex(2)> {1, 2, 3} |> then(fn {1, a, b} -> {a, b} end)
> {2, 3}
>
>
>
> # fall back to nil or some other value
>
> iex(4)> 1 |> then(fn {1, a, b} -> {a, b}; _ -> nil end)
> nil
>
>
>
> # assertive failure
>
> iex(5)> 1 |> then(fn {1, a, b} -> {a, b} end)
> ** (FunctionClauseError)
>
> ```
>
>
>
> `then` doesn't require that you learn any new API, you just do normal
> function stuff and everything works as expected. I'm not seeing a
> significant improvement with `pattern_filter` over this.
>
>
>
> - Ben
>
> On Thursday, December 15, 2022 at 3:48:39 PM UTC-5
> matt.fa...@covermymeds.com wrote:
>
> Hi again. I’m new to this so apologies if I’m coming off as clueless or
> pushy. I’m wondering what, if any, next steps there are to advocate for
> this. Should I share the code? Given what I mentioned in the responses
> about using one variable or using a new `destructure`, is there still
> disagreement?
>
>
>
> Thanks!
>
> Matt F
>
>
>
> *From: *<elixir-l...@googlegroups.com> on behalf of Sabiwara Yukichi <
> sabi...@gmail.com>
> *Reply-To: *"elixir-l...@googlegroups.com" <elixir-l...@googlegroups.com>
> *Date: *Tuesday, December 13, 2022 at 6:55 PM
> *To: *"elixir-l...@googlegroups.com" <elixir-l...@googlegroups.com>
> *Subject: *[EXTERNAL] Re: [elixir-core:11213] [proposal] Use patterns to
> filter data (good for pipes)
>
>
>
> This email came from a source outside of CoverMyMeds. Use caution when
> clicking on links or replying with confidential information.
> ------------------------------
>
> This is an interesting idea, but maybe `then/2` (or case/2 if you're fine
> piping in it) could already cover these cases quite well (equivalent to
> your pattern_filter! function):
>
>
>
> "$3.45" |> then(fn "$" <> money -> money end) |> String.to_float()
>
> "$3.45" |> case do "$" <> money -> money end |> String.to_float()
>
>
>
> The non-raising alternative might be slightly more verbose because you
> need a second clause. But most of the time (like your money example), the
> next step of the pipe might fail on nil anyway. Or maybe a with/1 pipeline
> might work better than the pipe operator if you want a succession of
> happy-path matches?
>
>
>
> If we move forward, it might be better to explicitly declare the returned
> expression, not just infer it from dangling variables: it isn't obvious
> what should `{a, b}` or `{a, b, a}` return. Something like:
>
>
>
> {1, 2, 1} |> pattern_filter(b <- {a, b, a})
>
>
>
> Le mer. 14 déc. 2022 à 05:50, 'Matt Farabaugh' via elixir-lang-core <
> elixir-l...@googlegroups.com> a écrit :
>
> All,
>
>
>
> I wrote a macro which allows for using a pattern to essentially extract a
> value from a data structure:
>
>
>
>
> @doc """
> Filter a value out of data using a pattern with one variable. Returns a
> default value
> if no match. Raises if pattern contains no variables or more than one
> variable.
>
> ## Examples
>
> iex> "$3.45" |> PatternHelpers.pattern_filter("$" <> money) |>
> String.to_float()
> 3.45
>
> iex> {1,2,3} |> PatternHelpers.pattern_filter({1,_,a})
> 3
>
> iex> %{a: 1, b: 2} |> PatternHelpers.pattern_filter(%{a: 9, b: b})
> nil
>
> iex> %{a: 1, b: 2} |> PatternHelpers.pattern_filter(%{a: 9, b: b}, "???")
> "???"
> """
>
>
>
> And an unsafe version:
>
>
>
> @doc """
> See `pattern_filter/3`. Raises if no match.
>
> ## Examples
>
> iex> {1,2,3} |> PatternHelpers.pattern_filter!({9,_,b})
> ** (MatchError) no match of right hand side value: {1, 2, 3}
> """
>
>
>
> This is my first proposal. Please let me know if this idea is worth some
> attention, and how I might better do my part to present it. I have code
> obviously but I'm not sure this is the place for it.
>
>
>
> Thanks,
>
> Matt F
>
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