[Haskell-cafe] indexed writer monad

[Nicholls, Mark]

Ah that assumes I know what a category is! (I did find some code that claimed the same thing)....maths doesn't scare me (much), and I suspect its nothing complicated (sounds like a category is a tuple then! Probably not), but I don't want to read a book on category theory to write a bit of code...yet.

Ideally there would be a chapter in something like "learn you an indexed Haskell for the great good".

Then I could take the code, use it...mess about with it...break it...put it back together in a slightly different shape and....bingo...it either works...or I find theres a good reason why it doesn't....(or I post a message to the café). 

-----Original Message-----
From: Roman Cheplyaka [mailto:roma at ro-che.info] 
Sent: 25 March 2015 2:46 PM
To: Nicholls, Mark; haskell-cafe at haskell.org
Subject: Re: [Haskell-cafe] indexed writer monad

An indexed monoid is just a Category.

On 25/03/15 16:32, Nicholls, Mark wrote:
> Anyone?
> 
>  
> 
> I can handle monads, but I have something (actually in F#) that feels 
> like it should be something like a indexed writer monad (which F# 
> probably wouldn't support).
> 
>  
> 
> So I thought I'd do some research in Haskell.
> 
>  
> 
> I know little or nothing about indexed monad (though I have built the 
> indexed state monad in C#).
> 
>  
> 
> So I would assume there would be an indexed monoid (that looks at bit 
> like a tuple?).
> 
>  
> 
> e.g.
> 
>  
> 
> (a,b) ++ (c,d) = (a,b,c,d)
> 
> (a,b,c,d) ++ (e) = (a,b,c,d,e)
> 
>  
> 
> ?
> 
>  
> 
> There seems to be some stuff about "update monads", but it doesn't 
> really look like a writer.
> 
>  
> 
> I could do with playing around with an indexed writer, in order to get 
> my head around what I'm doing..then try and capture what I'm 
> doing.then try (and fail) to port it back.
> 
>  
> 
>  
> 
> 
> 
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MTV Networks International, MTV Networks UK & Ireland, Greenhouse, Nickelodeon Viacom Consumer Products, VBSi, Viacom Brand Solutions International, Be Viacom, Viacom International Media Networks and VIMN and Comedy Central are all trading names of MTV Networks Europe.  MTV Networks Europe is a partnership between MTV Networks Europe Inc. and Viacom Networks Europe Inc.  Address for service in Great Britain is 17-29 Hawley Crescent, London, NW1 8TT.