Difference between Haskell ListT, LogicT and ChoiceT

Question

What is the difference between these three monad transformers?

You should probably link to the docs for the types you're referring to and make your question more specific. — jberryman
– jberryman, Commented Jan 2, 2013 at 16:24
Please be more specific -- do you mean just the MonadTrans instance for these types, or their behavior in general? — Don Stewart
– Don Stewart, Commented Jan 2, 2013 at 16:25

ertes · Accepted Answer · 2013-01-02 16:50:30Z

26

Well, first of all ListT is not a true monad transformer. It disobeys the associativity law for certain underlying monads. It is also pretty slow, as is the monadic interface to lists in general. It is built on actual lists internally.

LogicT is probably the best choice for list-like monad transformers. It not only implements a proper monad transformer, but also some very useful combinators for fair list products.

ChoiceT is my own work. It is basically just a CPSed version of LogicT and is inspired by both LogicT and the ChoiceT from monadLib. It's very fast, often outperforming (non-transformed) lists, but the types may be scary and you are bound to the result type, which may be in your way sometimes.

Conclusion: If you're serious, use LogicT.

answered Jan 2, 2013 at 16:50

ertes

2763 silver badges2 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

user824425 Over a year ago

Am I right in assuming that runLogicT and runChoiceT are folds?

C. A. McCann Over a year ago

@Tinctorius: Both LogicT and ChoiceT encode lists as folds of some sort anyway, and as usual the "run" functions just unwrap that. Folds are already similar to a CPS'd list, and ChoiceT adds an extra layer of proper CPS on top of that, which is why it has a type signature only a mother could love. ;]

rgrinberg Over a year ago

Would you mind describing this "proper CPS" in a little more detail or giving a reference? I originally thought that logictt was already basically a cpd's version of ListT done right

Collectives™ on Stack Overflow

Difference between Haskell ListT, LogicT and ChoiceT

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related