[Haskell-cafe] Re: State nested structures
Horribly enough this one seems to work...
mapOnBofA :: SB a - SA a
mapOnBofA mf = get = \st@(A {b=temp}) -
let (ans,temp2) = runState mf temp
in put (st { b=temp2}) return ans
There is nothing horrible about that. You just run a new isolated
computation in the State Monad for B and use its results. More or less
see same solution as Dupont's.
@Dupont:
telling from your possible use case and your last post with your MAP-
Problem, these two are very similar. You have a monad and inside your
monad you temporarily want to run some computation in another Monad. I
think Monad-Transformers are maybe the better option for you
(especially your interpreter-Problem was a good use case for StateT/
ErrorT instead of State and some Either inside it...).
On 29 Okt., 17:35, Stephen Tetley stephen.tet...@gmail.com wrote:
2010/10/29 Dupont Corentin corentin.dup...@gmail.com:
Also, I can't manage to write the more generic function SB x - SA x.
However, I'd have to question why you want both SA and SB as state
functional types. Having inner runState's is sometimes good practice
(its an instance of the Local Effect pattern identified by Ralf
Laemmel and Joost Visser), but if you have it commonly I'd suspect
you design is somehow contrived and could be simplified.
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Re: [Haskell-cafe] Re: State nested structures
Thank you for your responses. I will look at monad transformers.
I already use them I think because actually I use something like StateT Game
IO a.
You mean I have to implement my own instance?
Oh, can you call me Corentin? This is my name ;)
Cheers,
Corentin
On Fri, Oct 29, 2010 at 6:19 PM, steffen steffen.sier...@googlemail.comwrote:
Horribly enough this one seems to work...
mapOnBofA :: SB a - SA a
mapOnBofA mf = get = \st@(A {b=temp}) -
let (ans,temp2) = runState mf temp
in put (st { b=temp2}) return ans
There is nothing horrible about that. You just run a new isolated
computation in the State Monad for B and use its results. More or less
see same solution as Dupont's.
@Dupont:
telling from your possible use case and your last post with your MAP-
Problem, these two are very similar. You have a monad and inside your
monad you temporarily want to run some computation in another Monad. I
think Monad-Transformers are maybe the better option for you
(especially your interpreter-Problem was a good use case for StateT/
ErrorT instead of State and some Either inside it...).
On 29 Okt., 17:35, Stephen Tetley stephen.tet...@gmail.com wrote:
2010/10/29 Dupont Corentin corentin.dup...@gmail.com:
Also, I can't manage to write the more generic function SB x - SA x.
However, I'd have to question why you want both SA and SB as state
functional types. Having inner runState's is sometimes good practice
(its an instance of the Local Effect pattern identified by Ralf
Laemmel and Joost Visser), but if you have it commonly I'd suspect
you design is somehow contrived and could be simplified.
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[Haskell-cafe] Re: State nested structures
Nothing hinders you writing:
StateT Game (StateT A IO)
or
GameT mt = ErrorT Err (StateT Game (mt IO))
with mt being another Monad-Transformer
Monad-Transformers can be quite tricky. The point is you don't have to
create new Monad instances.
On 29 Okt., 18:46, Dupont Corentin corentin.dup...@gmail.com wrote:
Thank you for your responses. I will look at monad transformers.
I already use them I think because actually I use something like StateT Game
IO a.
You mean I have to implement my own instance?
Oh, can you call me Corentin? This is my name ;)
Cheers,
Corentin
On Fri, Oct 29, 2010 at 6:19 PM, steffen
steffen.sier...@googlemail.comwrote:
Horribly enough this one seems to work...
mapOnBofA :: SB a - SA a
mapOnBofA mf = get = \st@(A {b=temp}) -
let (ans,temp2) = runState mf temp
in put (st { b=temp2}) return ans
There is nothing horrible about that. You just run a new isolated
computation in the State Monad for B and use its results. More or less
see same solution as Dupont's.
@Dupont:
telling from your possible use case and your last post with your MAP-
Problem, these two are very similar. You have a monad and inside your
monad you temporarily want to run some computation in another Monad. I
think Monad-Transformers are maybe the better option for you
(especially your interpreter-Problem was a good use case for StateT/
ErrorT instead of State and some Either inside it...).
On 29 Okt., 17:35, Stephen Tetley stephen.tet...@gmail.com wrote:
2010/10/29 Dupont Corentin corentin.dup...@gmail.com:
Also, I can't manage to write the more generic function SB x - SA x.
However, I'd have to question why you want both SA and SB as state
functional types. Having inner runState's is sometimes good practice
(its an instance of the Local Effect pattern identified by Ralf
Laemmel and Joost Visser), but if you have it commonly I'd suspect
you design is somehow contrived and could be simplified.
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[Haskell-cafe] Re: State nested structures
you can find a nice introduction on using monad transformers by
developing an interpreter at [1] and a little more detailed one at [2]
[1]http://www.grabmueller.de/martin/www/pub/Transformers.pdf
[2]http://www.haskell.org/all_about_monads/html/
On 29 Okt., 18:46, Dupont Corentin corentin.dup...@gmail.com wrote:
Thank you for your responses. I will look at monad transformers.
I already use them I think because actually I use something like StateT Game
IO a.
You mean I have to implement my own instance?
Oh, can you call me Corentin? This is my name ;)
Cheers,
Corentin
On Fri, Oct 29, 2010 at 6:19 PM, steffen
steffen.sier...@googlemail.comwrote:
Horribly enough this one seems to work...
mapOnBofA :: SB a - SA a
mapOnBofA mf = get = \st@(A {b=temp}) -
let (ans,temp2) = runState mf temp
in put (st { b=temp2}) return ans
There is nothing horrible about that. You just run a new isolated
computation in the State Monad for B and use its results. More or less
see same solution as Dupont's.
@Dupont:
telling from your possible use case and your last post with your MAP-
Problem, these two are very similar. You have a monad and inside your
monad you temporarily want to run some computation in another Monad. I
think Monad-Transformers are maybe the better option for you
(especially your interpreter-Problem was a good use case for StateT/
ErrorT instead of State and some Either inside it...).
On 29 Okt., 17:35, Stephen Tetley stephen.tet...@gmail.com wrote:
2010/10/29 Dupont Corentin corentin.dup...@gmail.com:
Also, I can't manage to write the more generic function SB x - SA x.
However, I'd have to question why you want both SA and SB as state
functional types. Having inner runState's is sometimes good practice
(its an instance of the Local Effect pattern identified by Ralf
Laemmel and Joost Visser), but if you have it commonly I'd suspect
you design is somehow contrived and could be simplified.
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