Comments on A Neighborhood of Infinity: Grok Haskell Monad Transformers

Here's another nice and thorough and typeset :...

2012-01-19T18:58:42.401-08:00

Here's another nice and thorough and typeset :-) tutorial, posted shortly after sigfpe's original:

http://www.grabmueller.de/martin/www/pub/Transformers.en.html

Can not agree more with your comments on those fak...

2011-07-20T17:19:53.216-07:00

Can not agree more with your comments on those fake tutorials. This is just what I want to know. After using that for few weeks, I will begin to understand what Transformer really is.

Can not agree any more with your comments on those...

2011-07-20T17:18:03.479-07:00

Can not agree any more with your comments on those egghead's explanation on Monad Transformers. Thanks a lot. Really what I want to know.

Yeah, I'm going to have to agree with sigfpe.....

2010-11-30T22:24:14.922-08:00

Yeah, I'm going to have to agree with sigfpe... it's really just up to you how you want to do it. Sometimes multiple solutions stink!

For those wondering why you would want to use this...

2009-03-25T23:16:00.000-07:00

For those wondering why you would want to use this: as an example, I'm trying to implement Ruby Quiz 19 (Yahtzee). How am I supposed to set up an interactive loop with the user and save the current score and random state (for die rolls) throughout the loop? You can't do IO () stuff like putStrLn to show dice rolls while using State (Score,StdGen) x because your return type is no longer IO (). But with something like the test5 example, it's now entirely possible. A terrible workaround would've been to use IO () to read/write the state to a file... Now I can StateT (Score,StdGen) IO () and all is solved.

chessguy,

It's up to you. If you're bothere...

2009-02-21T16:10:00.000-08:00

chessguy,

It's up to you. If you're bothered by the lack of symmetry from having a StateT and a State then you can use the Identitiy monad.

Hmm, do you really need to wrap this around Identi...

2009-02-21T15:44:00.000-08:00

Hmm, do you really need to wrap this around Identity? Can't you just stack StateT on top of State to just get sort of a DoubleState monad?

This post is really great. Thanks!

2008-03-23T13:16:00.000-07:00

This post is really great. Thanks!

Very helpful post, thanks!

One thing - did ...

2007-12-03T06:44:00.000-08:00

Very helpful post, thanks!

One thing - did you mean to say "Try :type test3 in ghci." rather than :type go3 ?

The latter just yields:
go3 :: (Integer, [Char])

Tim,

Exactly. Except that if you just have ...

2007-05-25T17:44:00.000-07:00

Tim,

Exactly. Except that if you just have two types then one can be an ordinary monad, and the other can be a monad transformer. Or you can use three levels where both the reader and the writer are monad transformers and they are applied to the identity monad. (I do the former in this post.)

So, if I wanted two kinds of state, one readable a...

2007-05-25T17:09:00.000-07:00

So, if I wanted two kinds of state, one readable and one readable and writable, I could wrap a StateT in a ReaderT? Or vice versa?

I STILL can't think of one real-world reaso...

2007-04-26T23:22:00.000-07:00

I STILL can't think of one real-world reason why I'd want to use one. I just don't get it (yet).

Thanks. I found this quite useful.

2007-04-09T06:41:00.000-07:00

Thanks. I found this quite useful.

Thanks. Great post.

2007-04-06T16:09:00.000-07:00

Thanks. Great post.

Thanks, like you I had read about monad transforme...

2006-09-13T01:56:00.000-07:00

Thanks, like you I had read about monad transformers and thought "but why on earth would I want to use one?".

Pete,

I was going to post this very example...

2006-08-15T18:47:00.000-07:00

Pete,

I was going to post this very example on the Haskell Wiki but I had trouble figuring out how to do this. I'm happy for you to do it. If you want, add a link back to here.

If I remember I'll write an example that doesn't use 'lift' and post it here. Otherwise search for "Looking for basic state transformer example" on USENET where I first posted an example. (The title of the USENET post is wrong, I meant to say "monad" but said "state" by accident.)

Great post! I've been struggling with the concept ...

2006-08-15T17:56:00.000-07:00

Great post! I've been struggling with the concept of monad transformers. This post was very concise and to the point without obfuscating the reader with unnecessary details. Would it be possible to take the content of your post to one of the more public Haskell wikis (of course with proper attribution)? I wish I had discovered this much sooner!

One followup question related to the "update" at the end of the post. It's not clear to me when you say one doesn't always have to use lift. Could you give a concrete example?

Comments on A Neighborhood of Infinity: Grok Haskell Monad Transformers

Here's another nice and thorough and typeset :...

Can not agree more with your comments on those fak...

Can not agree any more with your comments on those...

Yeah, I'm going to have to agree with sigfpe.....

For those wondering why you would want to use this...

chessguy,It's up to you. If you're bothere...

Hmm, do you really need to wrap this around Identi...

This post is really great. Thanks!

Very helpful post, thanks!One thing - did ...

Tim,Exactly. Except that if you just have ...

So, if I wanted two kinds of state, one readable a...

I STILL can't think of one real-world reaso...

Thanks. I found this quite useful.

Thanks. Great post.

Thanks, like you I had read about monad transforme...

Pete,I was going to post this very example...

Great post! I've been struggling with the concept ...

chessguy,

It's up to you. If you're bothere...

Very helpful post, thanks!

One thing - did ...

Tim,

Exactly. Except that if you just have ...

Pete,

I was going to post this very example...