#9557: Deriving instances is slow -------------------------------------+------------------------------------- Reporter: Feuerbach | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Resolution: | Keywords: Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: | Blocked By: None/Unknown | Related Tickets: #8731 Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by rwbarton): Deriving a lot of instances for a lot of large types generates a lot of code. Language.Haskell.Exts.Annotated.Syntax desugared to a program with 126,396 terms and took 24.2 seconds to build (with -O0). By comparison, the longest (in terms of lines, roughly 2100) module Language.Haskell.Exts.Annotated.ExactPrint desugared to a program with only 12,181 terms and it took 2.7 seconds to build. So, I don't think there is anything wrong with the speed of deriving instances specifically. Now, it's possible that instance deriving could be made to generate smaller code than it currently does for some particular classes... but I didn't notice anything amiss scanning through the generated instances for Decl (with `-dsuppress-all -ddump-deriv -ddump-to-file`). So, I don't really think deriving is to blame here. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9557#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler