Ok, that works. On to code reading and, hopefully, enlightenment.
Thanks, all.
Michael
--- On Sun, 12/26/10, Daniel Fischer wrote:
From: Daniel Fischer
Subject: Re: [Haskell-cafe] Intro to monad transformers
To: haskell-cafe@haskell.org
Cc: "michael rice" , "David Menendez
On Sunday 26 December 2010 21:21:00, michael rice wrote:
> Ok, changed the last line and deleted the bad line. Maybe someone could
> recommend a better example?
>
> Michael
>
> =
>
> Prelude> :l test5
> [1 of 1] Compiling Main ( test5.hs, interpreted )
>
> test5.hs:16:4:
>
hen generalising the type(s) for `mplus'
In the instance declaration for `MonadPlus (MaybeT m)'
Failed, modules loaded: none.
--- On Sun, 12/26/10, David Menendez wrote:
From: David Menendez
Subject: Re: [Haskell-cafe] Intro to monad transformers
To: "michael rice"
Cc: h
On Sun, 26 Dec 2010, David Menendez wrote:
instance Show (MaybeT m a)
This is never valid. You've defined show, shows, and showsPrec in terms of each
other, creating
unbounded recursion. Delete it.
Unfortunately, the -Wall option of GHC won't help here, since all the
methods are defi
On Sunday 26 December 2010 20:00:02, michael rice wrote:
> I lifted the code below from here:
>
> http://en.wikibooks.org/wiki/Haskell/Monad_transformers
>
> Since the wiki page doesn't say what needs to be imported, I'm guessing.
>
> Not sure what is happening. Maybe someone can tell me.
It loops
On Sun, 26 Dec 2010, Antoine Latter wrote:
I haven't had a chance to dig into your example, but you might want to try the
maybeT library:
http://hackage.haskell.org/package/MaybeT
That way you could try to narrow down where the error is coming from.
MaybeT is also part of transformers libr
On Sun, Dec 26, 2010 at 2:00 PM, michael rice wrote:
> instance Monad m => MonadPlus (MaybeT m) where
> mzero = MaybeT $ return Nothing
> mplus x y = MaybeT $ do maybe_value <- runMaybeT x
> case maybe_value of
> Nothing
> instance Monad m => MonadPlus (MaybeT m) where
> mzero = MaybeT $ return Nothing
> mplus x y = MaybeT $ do maybe_value <- runMaybeT x
> case maybe_value of
> Nothing-> runMaybeT y
> Just
On Dec 26, 2010 2:01 PM, "michael rice" wrote:
>
> I lifted the code below from here:
>
> http://en.wikibooks.org/wiki/Haskell/Monad_transformers
>
> Since the wiki page doesn't say what needs to be imported, I'm guessing.
>
> Not sure what is happening. Maybe someone can tell me.
>
> Michael
>
I
On 26 December 2010 19:00, michael rice wrote:
>
> I lifted the code below from here:
>
> http://en.wikibooks.org/wiki/Haskell/Monad_transformers
>
> Since the wiki page doesn't say what needs to be imported, I'm guessing.
>
> Not sure what is happening. Maybe someone can tell me.
> instance Mona
I lifted the code below from here:
http://en.wikibooks.org/wiki/Haskell/Monad_transformers
Since the wiki page doesn't say what needs to be imported, I'm guessing.
Not sure what is happening. Maybe someone can tell me.
Michael
==
import Control.Monad
import Control.Monad.Trans.Cl
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