Re: [elixir-core:6223] Elixir way to handle errors in pipes

[Louis Pilfold]

Hi!

with is the right tool when you want this kind of error handling in these
function pipelines :)

Cheers,
Louis

On 15 Aug 2016 12:12, "Alvise Susmel"  wrote:

> Hi,
>
> I've started thinking about this, as maybe many of you, when I needed to
> stop the pipe when an error is returned. I've seen that there are different
> conversation about this, but I haven't clear what is the *elixir way* to
> handle errors using pipes.
>
> I see two ways for achieving the same result.* The first* is to use the
> *pipe* *|>* and for each function catch the error and propagate it down.
> The error has to be always returned with the same pattern, like {:error,
> reason}
>
> connect
> |> receive_image
> |> resize
> |> rotate
> |> save
>
>
> If *receive_image* returns an error,  *resize* needs to handle it
>
> def resize({:error, _}=error), do:error
>
> and to propagate it down through the pipe. So *rotate* needs to do the
> same, etc..
>
> *The* *second* way I see is using the *with*, which to me seems to be
> more generic (and less clean)
>
> with {:ok, pid} <- connect,
>{:ok, image} <- receive_image(pid),
>{:ok, resized_image} <- resize(image),
>   {:ok, rotated_image} <- rotate(resized_image),
>   :ok <- save(rotated_image)
> do: IO.puts "saved"
>
>
> Now, the cool thing about *with* is that when one of the assignments
> fails, it exits returning the value that failed the pattern match.
>
> So, to you, what is the elixir way on handling the return errors on pipes
> ? Could *"with" *be seen as a new (and more generic) way of piping with
> error handling ?
>
> Thanks
>
> Alvise
>
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[elixir-core:6223] Elixir way to handle errors in pipes

[Alvise Susmel]

Hi, 

I've started thinking about this, as maybe many of you, when I needed to 
stop the pipe when an error is returned. I've seen that there are different 
conversation about this, but I haven't clear what is the *elixir way* to 
handle errors using pipes. 

I see two ways for achieving the same result.* The first* is to use the 
*pipe* *|>* and for each function catch the error and propagate it down. 
The error has to be always returned with the same pattern, like {:error, 
reason} 

connect
|> receive_image
|> resize
|> rotate
|> save


If *receive_image* returns an error,  *resize* needs to handle it

def resize({:error, _}=error), do:error

and to propagate it down through the pipe. So *rotate* needs to do the 
same, etc..

*The* *second* way I see is using the *with*, which to me seems to be more 
generic (and less clean)

with {:ok, pid} <- connect,
   {:ok, image} <- receive_image(pid),
   {:ok, resized_image} <- resize(image),
  {:ok, rotated_image} <- rotate(resized_image),
  :ok <- save(rotated_image)
do: IO.puts "saved"


Now, the cool thing about *with* is that when one of the assignments fails, 
it exits returning the value that failed the pattern match. 

So, to you, what is the elixir way on handling the return errors on pipes ? 
Could *"with" *be seen as a new (and more generic) way of piping with error 
handling ?

Thanks

Alvise

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