#9198: large performance regression in type checker speed in 7.8 -------------------------------------------------+------------------------- Reporter: carter | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Compiler (Type checker) | Version: 7.8.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time performance bug | Unknown/Multiple Test Case: | Difficulty: Blocking: | Unknown | Blocked By: | Related Tickets: -------------------------------------------------+------------------------- Comment (by simonpj): The types really do get twice as large each time you add an `a`, I think. Are you certain that 7.6 is really fast? It got slow for me, just as 7.8 does, and not surprisingly so. These "big type" examples are pretty rare in practice, but even basic old Hindley-Milner type inference is worst-case exponential in program size. That said, GHC makes it worse by dragging these large type right through the compiler pipeline; it's a price we pay for a properly typed intermediate language. See [http://research.microsoft.com/en- us/um/people/simonpj/papers/variant-f/index.htm Scrap your type applications] for a way to improve these bad cases -- at a cost in compiler code complexity. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9198#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler