Daniel Carrera wrote:
It looks like Haskell doesn't do very well. It seems to be near the bottom of the pile in most tests. Is this due to the inherent design of Haskell or is it merely the fact that GHC is young and hasn't had as much time to optimize as other compilers?
I don't think it's that bad. It depends on the particular test, but it's almost comparable to Java, iirc. On some tests, it's terrible, though.
For example, another very slow language is Ruby. In Ruby's case, there is a design factor that will always make it slow. I wonder if Haskell is in a smilar situation.
Haskell's syntax and type system are powerful enough that technically there are a lot of optimizations possible without involving FFI. It may become ugly, though, and less and less safe e.g. if you have to use unsafeWrite's to update arrays to eliminate boundchecks, etc. A lot of the benchmark problems (at least the ones GHC seems to do worse than usual, e.g. http://shootout.alioth.debian.org/gp4/benchmark.php?test=revcomp&lang=all) involve some sort of string processing. Idiomatic Haskell dictates that one uses a linked list of Char's because FastString is not part of the language. That is a lot of overhead for values as small as one byte. Also, the input string is 25M characters long in the revcomp case, thus there's a lot of difference between reversing it with and without in-place updates. If you look at the OCaml implementations, they usually use references, in-place updates and compile with boundchecks disabled (but that is idiomatic ocaml code). However, I don't think it is right to downplay these benchmarks. Such little tasks exist in one form or another in bigger programs. Perhaps we should include mutable arrays in 'idiomatic' Haskell as well. Otherwise it is similar to proposing std::getline() take a std::List<Char> as an argument from a performance point of view. And it's not right to blame naive implementors, either. I couldn't have guessed that the see the difference between the two haskell implementations for sum-file would be so massive. It's a pity that the super-slow version could very well be the version your coworker would have written even if you wouldn't. Cheers, Koray