Re: [MirageOS-devel] result-y errors and MirageOS 3

[Hannes Mehnert <hannes@xxxxxxxxxxx>]

Thomas,

thank you so much for your work on this!  this is much better now :)

hannes

On 23/12/2016 12:08, Thomas Gazagnaire wrote:
> All the 30 pull request (!!) have been merged. Please open an issue if you 
> see any strange errors related to error types.
> 
> We decided to use the following error scheme after few months of going back 
> and forth:
> 
> - Every mirage-type signature (e.g. BLOCK, FLOW, etc) now defines an `error` 
> type (and sometime `write_error` too) which can either be abstract or which 
> can be exposed as a private polymorphic variant, like `type error = private 
> [> `Closed]`
> - Every mirage-type signature now exposes a `pp_error` (and sometime 
> `pp_write_error`) which can print the errors. 
> - Some helper printers have been temporary defined in `Mirage_pp` (from the 
> `mirage-runtime` module) which will disappear completely before 3.0 (see 
> bellow).
> - Module implementing these signature can use richer error types extending 
> the base errors (see mirage-channel[0]). It is also perfectly fine to export 
> these enriched error types in the mli.
> 
> The helper printers will move to individual related packages, like 
> `Mirage_block.pp_error` (this specific function has already been moved, 
> during the the signature split that I started to implement in the same 
> patchset, to see how it works in practice; short answer: it works well). 
> 
> Individual packages (with pretty-printer and sometimes much more[1]) now 
> exists for:
>   - DEVICE (Mirage_device[2] in mirage-device)
>   - CONSOLE (Mirage_console[3] in mirage-console)
>   - TIME (Mirage_time[4] in mirage-time)
>   - PCLOCK and MCLOCK (Mirage_clock[5] in mirage-clock)
>   - RANDOM (Mirage_random[6] in mirage-random)
>   - BLOCK (Mirage_block[7] and mirage-block)
>   - FLOW (Mirage_flow[8] in mirage-flow)
> 
> And same thing for their respective lwt implementation (V1_LWT.CONSOLE is an 
> alias to Mirage_console_lwt.S in mirage-console-lwt, etc.)
> 
> Thanks for everyone involved, especially Thomas Leonard, Mindy Preston and 
> Hannes Mehnert for the groundwork and Jeremy Yallop and Leo White for the 
> patience to explain the arcane of private polymorphic variants!
> 
> Best,
> Thomas
> 
> [0]: https://github.com/mirage/mirage-channel/blob/master/src/channel.ml#L35
> [1]: https://mirage.github.io/mirage-flow/
> [2]: https://mirage.github.io/mirage-device/
> [3]: https://mirage.github.io/mirage-console/
> [4]: https://mirage.github.io/mirage-time/
> [5]: https://mirage.github.io/mirage-clock/
> [6]: https://mirage.github.io/mirage-random/
> [7]: https://mirage.github.io/mirage-block/
> [8[: https://mirage.github.io/mirage-flow/
> 
> 
> 
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> 


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