pastebin - pastes related to haskell

<acura> @src null

<lambdabot> null []     = True

<lambdabot> null (_:_)  = False

* phlpp has quit IRC ("leaving")

<BMeph> > let f a b = a* (a+b) in f 0 0

<lambdabot>  0

* swiert has joined #haskell

<RayNbow> hmm, why is the second pattern (_:_) and not just _?

 

module Main where

 

 

 

mergesort :: Ord a => [a] -> [a]

mergesort []  =  []

mergesort [x] =  [x]

mergesort xs  =  merge (mergesort xs1) (mergesort xs2)

 

module Main where

 

 

 

mergesort :: Ord a => [a] -> [a]

mergesort []  =  []

mergesort [x] =  [x]

mergesort xs  =  merge (mergesort xs1) (mergesort xs2)

 

<RayNbow> hmm... I was wondering... [] is an instance of the Monad class... would it be useful to make other collection types (for example, Data.Set) also an instance of the Monad class?

<Cale> RayNbow: If it were possible, Set would be an instance of Monad

<Cale> RayNbow: The problem is that in order to implement bind and/or return, you need an instance of Ord for your element type, which isn't guaranteed by either of those.

<Cale> :t (>>=)

<lambdabot> forall (m :: * -> *) a b. (Monad m) => m a -> (a -> m b) -> m b

<RayNbow> why would you need Ord?

<Cale> (nothing here says that a or b will have an instance of Ord)

<Cale> Because in order to build a Data.Set, which is really a binary tree structure, you need to have an ordering on the elements. That's how it gets its efficiency.