Re: [Haskell-cafe] list utilities -- shouldn't these be in the hierarchical libs somewhere?

2007-12-18 Thread Jules Bean

Thomas Hartman wrote:


I found

  http://haskell.cs.yale.edu/haskell-report/List.html

  had many useful one off type list functions such as subsequences 
and permutations which are nowhere to be found in hoogle, Data.List, 
or the haskell hierarchical libs


Weird.

It's not very many. Other that those, I spotted: sums, products, 
elemIndexBy, elemBy.


I have no idea why they were removed between that version of the report 
and haskell98.


Jules
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Re: [Haskell-cafe] list utilities -- shouldn't these be in the hierarchical libs somewhere?

2007-12-18 Thread Twan van Laarhoven

Jules Bean wrote:


Thomas Hartman wrote:



I found

  http://haskell.cs.yale.edu/haskell-report/List.html

  had many useful one off type list functions such as subsequences 
and permutations which are nowhere to be found in hoogle, Data.List, 
or the haskell hierarchical libs



Weird.

It's not very many. Other that those, I spotted: sums, products, 
elemIndexBy, elemBy.


I have no idea why they were removed between that version of the report 
and haskell98.


For the ones you mention:

 - sums, products:

  The names don't make it clear what they do, I could for instance 
imagine sums being 'map sum'. And should it be a 'scanl' or 'scanr'?


 - elemIndexBy, elemBy:

  elemBy f x = any (f x)
  elemIndexBy f xs x = findIndex (f x) xs

On the other hand, I would love to see subsequences and permutations 
added to Data.List. In fact, I made a library proposal to make this 
happen, hopefully they will be added to the standard library soon.


Twan
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