#9742: The default definitions of foldl1 and foldr1 are too strict -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: ekmett Type: bug | Status: new Priority: normal | Milestone: 7.10.1 Component: Core | Version: 7.9 Libraries | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: Runtime | Blocked By: crash | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Description changed by dfeuer: Old description:

We currently have

{{{#!hs foldr1 :: (a -> a -> a) -> t a -> a foldr1 f xs = fromMaybe (error "foldr1: empty structure") (foldr mf Nothing xs) where mf x Nothing = Just x mf x (Just y) = Just (f x y) }}}

This has to traverse the entire list before it can do anything. What we want is

{{{#!hs mf x r = Just $ case r of Nothing -> x Just y -> f x y }}}

New description: We currently have {{{#!hs foldr1 :: (a -> a -> a) -> t a -> a foldr1 f xs = fromMaybe (error "foldr1: empty structure") (foldr mf Nothing xs) where mf x Nothing = Just x mf x (Just y) = Just (f x y) }}} This has to traverse the entire container before it can do anything. What we want is {{{#!hs mf x r = Just $ case r of Nothing -> x Just y -> f x y }}} -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9742#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9742: The default definitions of foldl1 and foldr1 are too strict -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: ekmett Type: bug | Status: patch Priority: normal | Milestone: 7.10.1 Component: Core | Version: 7.9 Libraries | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: Runtime | Blocked By: crash | Related Tickets: Test Case: | Blocking: | Differential Revisions: Phab:D416 | -------------------------------------+------------------------------------- Changes (by dfeuer): * status: new => patch * differential: => Phab:D416 Comment: This has met with a positive response on the libraries list. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9742#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9742: The default definitions of foldl1 and foldr1 are too strict -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: ekmett Type: bug | Status: patch Priority: normal | Milestone: 7.10.1 Component: Core | Version: 7.9 Libraries | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: Runtime | Blocked By: crash | Related Tickets: Test Case: | Blocking: | Differential Revisions: Phab:D423 | -------------------------------------+------------------------------------- Changes (by dfeuer): * differential: Phab:D416 => Phab:D423 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9742#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#9742: The default definitions of foldl1 and foldr1 are too strict -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: ekmett Type: bug | Status: closed Priority: normal | Milestone: 7.10.1 Component: Core | Version: 7.9 Libraries | Keywords: Resolution: fixed | Architecture: Unknown/Multiple Operating System: | Difficulty: Easy (less than 1 Unknown/Multiple | hour) Type of failure: Runtime | Blocked By: crash | Related Tickets: Test Case: | Blocking: | Differential Revisions: Phab:D423 | -------------------------------------+------------------------------------- Changes (by thomie): * status: patch => closed * resolution: => fixed -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9742#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler