Skip to content

Instantly share code, notes, and snippets.

Niklas Hambüchen nh2

Block or report user

Report or block nh2

Hide content and notifications from this user.

Learn more about blocking users

Contact Support about this user’s behavior.

Learn more about reporting abuse

Report abuse
View GitHub Profile
nh2 / realToFrac-rewrite-rules.txt
Created Feb 9, 2014
Discussion on #haskell about realToFrac performance
View realToFrac-rewrite-rules.txt
Does realToFrac compile to a no-op for (CFloat <-> Float / CDouble <-> Double)?
(14:27:30) kosmikus: nh2: it'll be a noop in many situations. CDouble normally is a newtype wrapper around Double. There are GHC Rule pragmas that'll turn realToFrac between Double and CDouble into a realToFrac between Double and Double by applying the constructor. Applying the constructor is a no-op, and there's a Double/Double instance having id as implementation.
(14:28:17) kosmikus: nh2: that being said, it's known that while simple applications of newtype constructors are newtypes, that doesn't translate to all contexts (such as mapping the constructor over a datastructure, for example)
(14:28:55) FreeFull: kosmikus: realToFrac isn't part of a typeclass though, it is defined as realToFrac = fromRational . toRational
(14:30:37) kosmikus: FreeFull: hm, you're right, I've been looking at the wrong place. let's check again.
(14:32:38) nh2: kosmikus, FreeFull: I really hope that realToFrac has rewrite rules for Double/CDouble and
nh2 / matmult.hs
Created Feb 9, 2014
Example of how Haskell's forM_ [1..N] is slow and custom loops are fast (lack of fusion)
View matmult.hs
{-# LANGUAGE ScopedTypeVariables, BangPatterns #-}
-- Example of how forM_ [1..N] is slow
module Main (main) where
import Prelude hiding (read)
import Control.Monad
import Data.Vector ((!), Vector)
import qualified Data.Vector as V
nh2 / time-natural.hs
Created Mar 1, 2014
Natural time in Haskell: `2 hours + 4 seconds`
View time-natural.hs
{-# LANGUAGE FlexibleInstances, GeneralizedNewtypeDeriving #-}
newtype TimeUnit = TimeUnit Integer -- how many microseconds
deriving (Eq, Show, Num)
instance Num (TimeUnit -> TimeUnit) where
fromInteger n = \(TimeUnit scale) -> TimeUnit (n * scale)
-- a + b = ... -- task for you
nh2 /
Last active Aug 29, 2015
Generates a git repository with dual history and some branches on top (for fixing a Jenkins performance bug)
# Creates a git repository called "testgit-generated"
# with two separate histories branching from the initial
# commit, each being 500 commits long.
# On top of each, we create 200 branches with one extra
# commit per branch.
# Should take around 30 seconds.
set -e
nh2 / k-smallest-benchmark.hs
Created Apr 6, 2014
Benchmark for finding the k-smallest element in a list in Haskell
View k-smallest-benchmark.hs
import Criterion.Main
import Data.List (sort)
import Data.Vector (Vector, fromList, unsafeThaw)
import qualified Data.Vector.Mutable as VM
import Data.Vector.Algorithms.Heap (select)
import Control.Monad.ST (runST)
import Data.Maybe (fromJust)
kSmallest1 :: Int -> [Int] -> Int
nh2 / reverse-deps-sorted.hs
Created Apr 10, 2014
Sorts and prints Haskell packages by number of reverse dependencies
View reverse-deps-sorted.hs
import Data.List (sort)
import qualified Data.Map as Map
import Distribution.PackDeps
import Control.Monad
main :: IO ()
main = do
newest <- loadNewest
let reverses = getReverses newest
nh2 / list-loop.hs
Last active Aug 29, 2015
Benchmark: forM_ [1..n] against manual loop
View list-loop.hs
{-# LANGUAGE BangPatterns, ScopedTypeVariables #-}
module Main (main) where
import Criterion.Main
import Control.Monad
import Data.Vector ((!), Vector)
import qualified Data.Vector as V
import qualified Data.Vector.Unboxed as U
import qualified Data.Vector.Unboxed.Mutable as UM
nh2 / reinterpret-cast.c
Created Apr 30, 2014
reinterpret_cast in C
View reinterpret-cast.c
#include <stdio.h>
int main(int argc, char const *argv[])
float f = 1.23;
int i = * (int *) &f;
printf("%d\n", i);
float f2 = * (float *) &f;
nh2 / generic-show.hs
Last active Aug 29, 2015
Haskell sorcery with Generics and Typeable for showing the structure of any value
View generic-show.hs
import GHC.Generics
import Data.Typeable
deriving instance Show (f p) => Show (M1 i c f p)
deriving instance (Show (f p), Show (g p)) => Show ((f :*:g) p)
deriving instance (Show (f p), Show (g p)) => Show ((f :+:g) p)
deriving instance (Show c) => Show (K1 i c p)
deriving instance Show (V1 p)
deriving instance Show (U1 p)
deriving instance Show D
nh2 / Haskell-Conditional-Compilation.txt
Created May 14, 2014
MIN_VERSION_base vs. __GLASGOW_HASKELL__ for conditional compilation
View Haskell-Conditional-Compilation.txt
nh2: does `#if MIN_VERSION_base(4,7,0)` fail when using ghci / do I need to build with cabal? I'm trying to get my packages 7.8-ready
thoughtpolice: that macro is only defined by Cabal, IIRC. so yes, you do need cabal
nh2: thoughtpolice: is what they describe in a valid workaround, using __GLASGOW_HASKELL__?
carter: nh2: yup, only in cbal
carter: yes
thoughtpolice: nh2: sure, __GLASGOW_HASKELL__ should be fine, since the accompanying version of base is fixed anyway
thoughtpolice: nh2: so you probably want something like '#if __GLASGOW_HASKELL__ >= 708'
thoughtpolice: nh2: but note __GLASGOW_HASKELL__ does not account for the minor version, so you can't distinguish base from for example
thoughtpolice: (although i think historically we've never bumped an update like that - only very minor bumps per release)
carter: thoughtpolice: edward just pointed out to me that GHC doesn't expose GHC minor version cpp
You can’t perform that action at this time.