[Haskell-cafe] What are "free" Monads?

Sebastian Fischer sebf at informatik.uni-kiel.de
Tue Mar 2 03:53:27 EST 2010

On Mar 2, 2010, at 5:59 AM, Dan Doel wrote:

>  http://haskell.org/haskellwiki/Free_monad
>  http://haskell.org/haskellwiki/Free_structure

Nice, thank you for writing this.

> Feel free to make suggestions/changes.

I enjoyed reading it although Section 3 is challenging for people  
(like me) who know algebra but do not know the exact meaning of the  
mentioned terminology from CT even if they have read about it before.  
It would be helpful to add intuitive explanations. For example, after

     "Simplest" (in the sense we want) structures in that category  
will then
     either be initial or terminal, and thus, freeness can be defined  
in terms
     of such universal constructions.

I missed sentences

     Intuitively, "initial" means that ... and thus relates to the  
     description because ...

     Final means ... and expresses the informal idea of ...

Similarly, subsequent uses of CT terminology (like 'forgetful functor'  
and 'natural transformation') could be related to intuitions given  
before (or new ones).


Underestimating the novelty of the future is a time-honored tradition.

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