[GHC] #3631: Overload the Prelude iterate to support list input

[GHC]

#3631: Overload the Prelude iterate to support list input
-----------------------------+----------------------------------------------
Reporter:  shelbymoore3      |          Owner:                  
    Type:  feature request   |         Status:  new             
Priority:  normal            |      Component:  Prelude         
 Version:  6.10.4            |       Severity:  normal          
Keywords:                    |       Testcase:                  
      Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
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 Had to overload the Prelude function iterate to support list input.  The
 overload could be global (should be added to Prelude), no need to wrap in
 where.  My example fibonacci sequence usage follows.


 {{{
     fibs = 0 : 1 : zipWith (+) fibs (tail fibs)
 }}}


 Make forward iteration explicit, and remove self referential space "leak"
 above due direct recursion on fibs.


 {{{
     fibs = iterate (\x -> last x + last init x) [ 0 : 1 ] where
         iterate :: ([a] -> [a]) -> [a] -> [a]
         iterate f x =  iterate f (x : (f x))
         -- iterate f x == [x, f x, f (f x), ...]
 }}}


     Or verbosely:


 {{{
         fibs = iterate (\x -> fib -1 + fib -2 where fib i = | i==-1=last x
 | i==-2=last init x) [ 0 : 1 ]
                 -- negative indices in local function fib offset from end
 of list
 }}}



 P.S. Note I not using HUGS nor GHC, this is just in my head.  The above
 are my unique solutions, didn't lift them from www.  I am just learning FP
 and Haskell for first time in my head past few days.  So this might be
 rubbish.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3631>
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