[Haskell-cafe] indexed writer monad

[Roman Cheplyaka]

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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