[Haskell-fr] Fw: Éclaircissements sur les monades

[Gautier DI FOLCO]

2014-03-27 6:07 GMT+01:00 Dan Popa <popavdan at yahoo.com>:

> Hi,
>
> Sorry for writing in english, I am not from France.
> Take a look here, please:
>
> http://www.haskell.org/haskellwiki/Modular_Monadic_Compilers_for_Programming_Languages
>
> The source  at  #3) on the above page is a code generator written using
> the State monad.
> The state monad is necessary because here it provides a sort of context,
> like a set of the global variables
> in imperative programming.
> And that is why we are using The State Monad, to simulate the
> use of a set of global (or local) variables, used to store values.
>
> Especially in this example, the lenghts of the pieces of generated code
> are stored in order to compute the length of the biggers codes, when they
> are catenated, (glued together).
>
> Other monads have specific use. Parser monad is used for glueing parsers,
> the list monad can simulate paralel computations and even backtracking
> (there is a backtracking monad too), the Maybe monad is used to make
> computations including Nothing in the set of values, etc.
>
> Basically monadic capsules can be seen like Christmas Giftts containing
> compuations. And monadic operators have two kind of use:
> - return is a package maker, it creates a capsule, a package, like
> wrapping a gift
> - bind is something like:  how to combine a function with a package. Open
> the package, compose functions, take care to produce an other package (or
> capsule).
>
> Hoping it helps,
> Sincerely yours,
> Dan Popa
>
>   ----- Forwarded Message -----
>  *From:* Gautier DI FOLCO <gautier.difolco at gmail.com>
> *To:* La liste Haskell Francophone <haskell-fr at haskell.org>
> *Sent:* Wednesday, March 26, 2014 12:10 PM
> *Subject:* [Haskell-fr] Éclaircissements sur les monades
>
> Bonjour,
>
> Vaste sujet en perspective : les monades.
> Je pense avoir compris le principe des monades (être en mesure d'effectuer
> des actions sur une valeur au sein d'un contexte), en revanche il y a deux
> choses que je ne comprends pas :
>  * La notion de contexte (ou de cadre de calcul) est un peu floue
>  * Pourquoi est-ce que les monades sont aptes à contenir les effets de
> bords (j'ai lu effectful computations) et pas d'autres typeclass (comme
> Applicative).
>
> Merci par avance pour vos réponses.
>
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>
State Monads are clearer to me, thanks.
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