#10837: Constant-time indexing of closed type family axioms -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: Type: task | Status: new Priority: low | Milestone: Component: Compiler | Version: 7.11 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Right now `CoAxiom` stores a list of `CoAxBranch`es in a `BranchList`. But it would be useful to actually have a constant-time indexing into axioms. One code fragment when I really wanted to have this feature is in `TcValidity.checkValidCoAxiom`: {{{#!hs -- Replace n-th element in the list. Assumes 0-based indexing. replace_br :: [CoAxBranch] -> Int -> CoAxBranch -> [CoAxBranch] replace_br brs n br = take n brs ++ [br] ++ drop (n+1) brs }}} I believe this code could be rewritten in a much more efficient way using constant-time indexing. The new data structure should most likely have a type that indicates whether the axiom is branched or not. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10837 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler