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by shakow 1863 days ago
> if a call at the beginning of the pipeline returns a tuple of `{:ok, result}`

In my understanding, pipeline are mostly reserved for “unfailable” operations operating on raw data; whereas the where/else/do macro is more oriented towards errors handling; would it work better in your case?
1 comments
klibertp 1863 days ago
I think you mean `with`, not `where`? Yes, it helps a bit in some cases, but it's not a replacement for a pipeline - mainly because you'd need to name your intermediate results and "thread" them through the calls yourself.

I think I gave a bad example, the better one would be a function returning datetime in the format of :erlang.localtime: `{{Year,Month,Day},{Hour,Min,Sec}}`. I would like to be able to use this value in a pipeline, by passing only a `{Hour, Min}` tuple to the next call in the pipeline.

With pattern_tap it looks like this:

    :erlang.localtime()
    |> tap({_, {H,M,_}} ~> {H, M})
    |> do_something
Without - there are at least 3-4 ways of doing this, each with pros and cons, but all of them are more verbose than pattern_tap. If you want a single value only, there's `elem`, but if you need a few - you're out of luck. `destructure` only works on lists, and `match?` only return a boolean, not whatever was matched.

`then` macro makes it a bit better, but you still need to create a lambda with the longhand syntax, which is exactly what I wanted to avoid, so it's hardly a solution, even though it may be the best way to do this for now...

EDIT: this is in contrast to Clojure, where maps and vectors are callable, and you get `juxt` in the stdlib. So it's not like pipelines in general can't support convenient extraction of subsets of data flowing through the pipe, it's just that Elixir decided not to support this.

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losvedir 1863 days ago
Hm, this works and is about as terse as `pattern_tap`:

    :erlang.localtime()
    |> case do; {_, {h,m,_}} -> {h, m}; end
    |> do_something
Not that I'd want to do that in production code, but I felt a bit nerd-sniped here, to see the shortest way I could find without dependencies.
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klibertp 1863 days ago
That's actually what pattern_tap's tap macro expands into :) See: https://github.com/mgwidmann/elixir-pattern_tap/blob/master/...
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shakow 1863 days ago
> I think you mean `with`, not `where`?

Indeed, my bad.

> the better one would be a function returning datetime in the format of :erlang.localtime: `{{Year,Month,Day},{Hour,Min,Sec}}`

I see what you mean. Yeah, I agree with the rest.

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