[Haskell-cafe] exceptions, errors, random

[Ivan Lazar Miljenovic]

On 21 June 2017 at 03:19, Dennis Raddle <dennis.raddle at gmail.com> wrote:
> Looking at my application needs, such as access to pseudorandom numbers and
> threads, does this suggest a particular course of action?

For randomness, probably mwc-random, carrying the seed around in a
StateT with IO on the bottom of the stack.

For multi-threaded: parallelism or concurrency?  Simon Marlow's
Parallel and Concurrent Programming in Haskell is an excellent book on
the topic: http://shop.oreilly.com/product/0636920026365.do

>
> D
>
>
> On Tue, Jun 20, 2017 at 1:40 AM, Ivan Lazar Miljenovic
> <ivan.miljenovic at gmail.com> wrote:
>>
>> There are two general schools of thought as to how to deal with
>> exceptions:
>>
>> * ExceptT/MonadError from transformers/mtl:
>>
>> http://www.mega-nerd.com/erikd/Blog/CodeHacking/Haskell/what_do_you_mean.html
>>
>> * The exceptions package (which is a lifted variant of
>> Control.Exception in base):
>> https://www.fpcomplete.com/blog/2016/11/exceptions-best-practices-haskell
>>
>> On 20 June 2017 at 15:53, Dennis Raddle <dennis.raddle at gmail.com> wrote:
>> > Just want to bump this request as I have not gotten a reply.
>> >
>> > On Fri, Jun 16, 2017 at 1:45 PM, Dennis Raddle <dennis.raddle at gmail.com>
>> > wrote:
>> >>
>> >> I am wondering what exception/error and random classes I should use for
>> >> my
>> >> application.
>> >>
>> >> The application will be doing Monte Carlo backtracking search. I want
>> >> it
>> >> to be multithreaded and run on all four cores on my MacBook.
>> >>
>> >> I need detailed error messages in order to investigate errors. So I
>> >> will
>> >> throw errors or exceptions, then catch them in lower functions and
>> >> annotate
>> >> them with the parameters or computations within the lower function,
>> >> then
>> >> re-throw until finally the exception pops into the terminal.
>> >>
>> >> Because it's multi-threaded, at least some parts will needs to be in
>> >> IO.
>> >> Also, because it's a Monte Carlo algorithm it will need to make
>> >> pseudorandom
>> >> choices.
>> >>
>> >> Perhaps I should put everything in the IO monad? This will give me
>> >> access
>> >> to threads and the standard generator seed. But how about throwing,
>> >> catching/rethrowing exceptions in IO? I have done this in pure code
>> >> before:
>> >> not sure if it's better to do it that way, in which case I could put
>> >> some
>> >> kind of state monad to hold the random seed together with an error
>> >> monad and
>> >> IO at the core of the monad stack.
>> >>
>> >> Any advice welcome.
>> >> D
>> >>
>> >
>> >
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>>
>>
>> --
>> Ivan Lazar Miljenovic
>> Ivan.Miljenovic at gmail.com
>> http://IvanMiljenovic.wordpress.com
>
>



-- 
Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com
http://IvanMiljenovic.wordpress.com