#3416: maximumBy uses too much stack
-----------------------------+----------------------------------------------
Reporter: bdonlan | Owner:
Type: bug | Status: new
Priority: normal | Component: libraries/base
Version: 6.10.4 | Severity: normal
Keywords: | Testcase:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
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maximumBy uses too much stack when working on long lists:
{{{
Prelude Data.List> maximumBy compare [1..1000000]
*** Exception: stack overflow
}}}
Here's a fixed implementation; the only change is replacing foldl1 with
foldl1'.
{{{
-- | The 'maximumBy' function takes a comparison function and a list
-- and returns the greatest element of the list by the comparison
function.
-- The list must be finite and non-empty.
maximumBy :: (a -> a -> Ordering) -> [a] -> a
maximumBy _ [] = error "List.maximumBy: empty list"
maximumBy cmp xs = foldl1' maxBy xs
where
maxBy x y = case cmp x y of
GT -> x
_ -> y
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3416>
GHC <http://www.haskell.org/ghc/>
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