#3631: Overload the Prelude iterate to support list input
---------------------------------+------------------------------------------
Reporter: shelbymoore3 | Owner:
Type: feature request | Status: closed
Priority: normal | Milestone:
Component: Prelude | Version: 6.10.4
Severity: normal | Resolution: wontfix
Keywords: | Difficulty: Unknown
Testcase: | Os: Unknown/Multiple
Architecture: Unknown/Multiple |
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Comment (by shelbymoore3):
Correction:
{{{
iterate f x y = y ++ iterate f (x ++ (f x)) (f x)
}}}
{{{
fibs = 0 : 1 : iterate (\x -> [last x + last init x]) [ 0 : 1 ] [] where
}}}
Alternative (IMHO the best):
{{{
iterate f x = x ++ iterate' f x [] where
iterate' f x y = y ++ iterate' f (x ++ (f x)) (f x)
}}}
{{{
fibs = iterate (\x -> [last x + last init x]) [ 0 : 1 ] where
}}}
Alternative (less general):
{{{
iterate :: ([a] -> a) -> [a] -> a -> [a]
iterate f x y = y : iterate f (x ++ [(f x)]) (f x)
}}}
{{{
fibs = 0 : iterate (\x -> last x + last init x) [0] 1 where
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3631#comment:16>
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