[Haskell-cafe] The mother of all functors/monads/categories

Max Bolingbroke batterseapower at hotmail.com
Sun Jun 27 12:38:42 EDT 2010

On 27 June 2010 14:30, Roman Leshchinskiy <rl at cse.unsw.edu.au> wrote:
> In that case, isn't D just the dictionary for (X d) and a value of type (d a)? I.e., couldn't we always define it as:
> data D d a where { D :: X d => d a -> D d a }

I wondered about this, but how would you write e.g. the "return"
method for Codensity? You don't have an input dictionary to work with.


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