#9545: Evaluate Takano Akio's foldrW/buildW fusion framework as a possible replacement for foldr/build -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: task | Status: closed Priority: normal | Milestone: Component: | Version: 7.9 libraries/base | Keywords: Resolution: wontfix | Architecture: Unknown/Multiple Operating System: | Difficulty: Project (more Unknown/Multiple | than a week) Type of failure: | Blocked By: None/Unknown | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Changes (by dfeuer): * status: new => closed * resolution: => wontfix Comment: Challenges seem to be piling up. The biggest problem is that no one has been able to find local criteria to ensure correctness. The interesting wrappers don't generally satisfy the trivial `wrap . unwrap = id` correctness condition; rather, they rely on more complex interactions with the loop bodies they're embedded in. To ensure correctness, we would need two things: 1. Rules about how a producer can/must use the wrapper, cons, and nil it receives, and 2. Rules about what properties the wrapper, cons, and nil a consumer uses must have to ensure correct behavior when used by a sufficiently well- behaved producer. In essence, these three things have to travel and transform ''together'' in a correct fashion as they travel from a consumer through transformers to a producer. Takano Akio did not write any such things down, and Joachim was unable to make contact. Joachim and Dan couldn't think of anything. Edward K. said this whole thing looked frightening. It may be that one of the wizards out there can come up with a way to make this work, but until then, I think it's probably best to set it aside. Joachim has some other ideas for addressing the underlying issues; hopefully one of them will work out. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9545#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler