Thanks for the reply, José. I was thinking that more ways to pattern match is a
good thing. I’m still new to the language so I might not have its philosophy
internalized yet.
I probably should have included at least the heads of the macros:
defmacro pattern_filter(value, pattern, default \\ nil)
defmacro pattern_filter!(value, pattern)
So the fallback can be specified as not nil. One of my examples returns “???”
when not matching. I was just trying to make it like `Map.get` in that sense.
So your example would become this:
case res do
{:ok, value} -> value
:error -> :default
end
|> pattern_filter({:ok, value}, :default)
I agree that it is less flexible than a case – maybe more akin to a ternary
with a pattern.
I also think that if you needed to extract two variables, then pattern_filter
wouldn’t be the right tool.
In any case, I really appreciate how much thoughtful feedback I gained from you
and the others who replied! I’m glad to be working in Elixir.
From: <elixir-lang-core@googlegroups.com> on behalf of José Valim
<jose.va...@dashbit.co>
Reply-To: "elixir-lang-core@googlegroups.com"
<elixir-lang-core@googlegroups.com>
Date: Thursday, December 15, 2022 at 4:58 PM
To: "elixir-lang-core@googlegroups.com" <elixir-lang-core@googlegroups.com>
Subject: Re: [EXTERNAL] Re: [elixir-core:11222] [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.
________________________________
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<mailto: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<mailto:elixir-lang-core@googlegroups.com>>
on behalf of Ben Wilson <benwilson...@gmail.com<mailto:benwilson...@gmail.com>>
Reply-To:
"elixir-lang-core@googlegroups.com<mailto:elixir-lang-core@googlegroups.com>"
<elixir-lang-core@googlegroups.com<mailto:elixir-lang-core@googlegroups.com>>
Date: Thursday, December 15, 2022 at 4:23 PM
To: elixir-lang-core
<elixir-lang-core@googlegroups.com<mailto: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<mailto: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<mailto:elixir-l...@googlegroups.com>> on
behalf of Sabiwara Yukichi <sabi...@gmail.com<mailto:sabi...@gmail.com>>
Reply-To: "elixir-l...@googlegroups.com<mailto:elixir-l...@googlegroups.com>"
<elixir-l...@googlegroups.com<mailto:elixir-l...@googlegroups.com>>
Date: Tuesday, December 13, 2022 at 6:55 PM
To: "elixir-l...@googlegroups.com<mailto:elixir-l...@googlegroups.com>"
<elixir-l...@googlegroups.com<mailto: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<mailto: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
--
You received this message because you are subscribed to the Google Groups
"elixir-lang-core" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to
elixir-lang-co...@googlegroups.com<mailto:elixir-lang-co...@googlegroups.com>.
To view this discussion on the web visit
https://groups.google.com/d/msgid/elixir-lang-core/4b65083e-6c36-4519-a0ed-fa2da8b61a9bn%40googlegroups.com<https://urldefense.com/v3/__https:/groups.google.com/d/msgid/elixir-lang-core/4b65083e-6c36-4519-a0ed-fa2da8b61a9bn*40googlegroups.com?utm_medium=email&utm_source=footer__;JQ!!LBRzLL-rxcoG!soAu7_j204hUseqlxMsemQMOhOz0yO8WygSZdV2t7WGq5iDQfDh-prkOc8PkTmo4vz08vKeE_ZmAZ19k2vMrPomauA$>.
--
You received this message because you are subscribed to the Google Groups
"elixir-lang-core" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to
elixir-lang-co...@googlegroups.com<mailto:elixir-lang-co...@googlegroups.com>.
To view this discussion on the web visit
https://groups.google.com/d/msgid/elixir-lang-core/CANnyohYy8hRvu2WD%2BMUEzWS2SxoA8eYk9PETOe8jGxr2tiuW%2BA%40mail.gmail.com<https://urldefense.com/v3/__https:/groups.google.com/d/msgid/elixir-lang-core/CANnyohYy8hRvu2WD*2BMUEzWS2SxoA8eYk9PETOe8jGxr2tiuW*2BA*40mail.gmail.com?utm_medium=email&utm_source=footer__;JSUl!!LBRzLL-rxcoG!soAu7_j204hUseqlxMsemQMOhOz0yO8WygSZdV2t7WGq5iDQfDh-prkOc8PkTmo4vz08vKeE_ZmAZ19k2vMQT4CMDA$>.
This electronic transmission is confidential and intended solely for the
addressee(s). If you are not an intended addressee, do not disclose, copy or
take any other action in reliance on this transmission. If you have received
this transmission in error, please delete it from your system and notify
CoverMyMeds LLC at pri...@covermymeds.com<mailto:pri...@covermymeds.com>. Thank
you.
--
You received this message because you are subscribed to the Google Groups
"elixir-lang-core" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to
elixir-lang-core+unsubscr...@googlegroups.com<mailto:elixir-lang-core+unsubscr...@googlegroups.com>.
To view this discussion on the web visit
https://groups.google.com/d/msgid/elixir-lang-core/a3878ce0-397a-4a42-86db-12f475d4498an%40googlegroups.com<https://urldefense.com/v3/__https:/groups.google.com/d/msgid/elixir-lang-core/a3878ce0-397a-4a42-86db-12f475d4498an*40googlegroups.com?utm_medium=email&utm_source=footer__;JQ!!LBRzLL-rxcoG!on2QXE44nv5hdEfuc6k2tBYeiokzX1sFBLI3f8X9DhKWbuoYllOks_N36dorMnl3olGY5AQpe23t11VHZnbpC4ZFxRr8K14$>.
This electronic transmission is confidential and intended solely for the
addressee(s). If you are not an intended addressee, do not disclose, copy or
take any other action in reliance on this transmission. If you have received
this transmission in error, please delete it from your system and notify
CoverMyMeds LLC at priv...@covermymeds.com<mailto:priv...@covermymeds.com>.
Thank you.
--
You received this message because you are subscribed to the Google Groups
"elixir-lang-core" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to
elixir-lang-core+unsubscr...@googlegroups.com<mailto:elixir-lang-core+unsubscr...@googlegroups.com>.
To view this discussion on the web visit
https://groups.google.com/d/msgid/elixir-lang-core/9DE6BF24-8902-45DA-8BC1-687037D4466A%40covermymeds.com<https://urldefense.com/v3/__https:/groups.google.com/d/msgid/elixir-lang-core/9DE6BF24-8902-45DA-8BC1-687037D4466A*40covermymeds.com?utm_medium=email&utm_source=footer__;JQ!!LBRzLL-rxcoG!qIgDGbe0PjEe33qr-AjSJyVTmpyDXGtKGyrPP6CV2CjP0GOJphJPwn0sTk1TlRy4V-bpdPfifHQG4eADEjROunLY-OjOFWk$>.
--
You received this message because you are subscribed to the Google Groups
"elixir-lang-core" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to
elixir-lang-core+unsubscr...@googlegroups.com<mailto:elixir-lang-core+unsubscr...@googlegroups.com>.
To view this discussion on the web visit
https://groups.google.com/d/msgid/elixir-lang-core/CAGnRm4KzqaLTtDKEz_rBx7W5waHao%3Dm9JMGJn%2BJ0Z9OeHMLW6w%40mail.gmail.com<https://urldefense.com/v3/__https:/groups.google.com/d/msgid/elixir-lang-core/CAGnRm4KzqaLTtDKEz_rBx7W5waHao*3Dm9JMGJn*2BJ0Z9OeHMLW6w*40mail.gmail.com?utm_medium=email&utm_source=footer__;JSUl!!LBRzLL-rxcoG!qIgDGbe0PjEe33qr-AjSJyVTmpyDXGtKGyrPP6CV2CjP0GOJphJPwn0sTk1TlRy4V-bpdPfifHQG4eADEjROunLYCvdsUlA$>.
This electronic transmission is confidential and intended solely for the
addressee(s). If you are not an intended addressee, do not disclose, copy or
take any other action in reliance on this transmission. If you have received
this transmission in error, please delete it from your system and notify
CoverMyMeds LLC at priv...@covermymeds.com. Thank you.
--
You received this message because you are subscribed to the Google Groups
"elixir-lang-core" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to elixir-lang-core+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/elixir-lang-core/EE645075-DFC9-4A4E-8CF5-CEE76BC748DB%40covermymeds.com.
