[Haskell-cafe] indexed writer monad

Nicholls, Mark nicholls.mark at vimn.com
Wed Mar 25 14:32:43 UTC 2015


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?)...


(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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