You’re actually doing pretty well to have a 51ms pause time with over 200Mb of live data. The system I work on has a larger max pause time with half that amount of live data. Your assumption is correct, the major GC pause time is directly proportional to the amount of live data, and unfortunately … Read more
You can pass the argument to ghc from ghc-mod as: $ ghc-mod lint *.hs -g -dsuppress-module-prefixes This will send the argument -dsuppress-module-prefixes to ghc.
It’s a bit silly really. Every library that comes with GHC is provided in no less than 4 flavours: static dynamic profiled GHCi The GHCi version is just the static version linked together in a single .o file. The other three versions all have their own set of interface files (.hi files) too. The profiled … Read more
GHC also gives an option to SPECIALIZE a type-class instance declaration. I tried this with the (expanded) code of Foo.hs, by putting the following: instance (Num r, V.Vector v r, Factored m r) => Num (VT v m r) where {-# SPECIALIZE instance ( Factored m Int => Num (VT U.Vector m Int)) #-} VT … Read more
This GHC Trac page also explains the passes fairly well. This page explains the optimization ordering, though, like the majority of the Trac Wiki, it is out of date. For specifics, the best thing to do is probably to look at how a specific program is compiled. The best way to see which optimizations are … Read more
GHC Core is the System FC language into which all Haskell is translated. The (approximate) grammar for Core is given by: Core is closely related to the simpler and better known System F. All transformations GHC does on the Core level are type-preserving refactorings of this Core representation, to improve performance. And, not so well … Read more
I don’t see any published version of syntactic whose signature for sugarSym uses those exact type names, so I’ll be using the development branch at commit 8cfd02^, the last version which still used those names. So, why does GHC complain about the fi in your type signature but not the one for sugarSym? The documentation … Read more
I agree with Dietrich Epp: it’s a combination of several things that make GHC fast. First and foremost, Haskell is very high-level. This enables the compiler to perform aggressive optimisations without breaking your code. Think about SQL. Now, when I write a SELECT statement, it might look like an imperative loop, but it isn’t. It … Read more
First of all, your function has the wrong type; I am pretty sure it should be (without the context) a -> (a -> b) -> b. GHC 7.10 is somewhat more helpful in pointing that out, because with your original code, it complains about a missing constraint Internal (a -> b) ~ (Internal a -> … Read more
Let’s start with a code example: foob :: forall a b. (b -> b) -> b -> (a -> b) -> Maybe a -> b foob postProcess onNothin onJust mval = postProcess val where val :: b val = maybe onNothin onJust mval This code doesn’t compile (syntax error) in plain Haskell 98. It requires … Read more