#3339: Data.Monoid: Add (<>) as a synonym for mappend
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Reporter: bos | Owner:
Type: proposal | Status: new
Priority: normal | Milestone: Not GHC
Component: libraries/base | Version: 6.10.3
Resolution: | Keywords:
Testcase: | Blockedby:
Difficulty: Unknown | Os: Unknown/Multiple
Blocking: | Architecture: Unknown/Multiple
Failure: None/Unknown |
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Comment(by nominolo):
Benchmarks checking whether changing associativity of (<>) in `pretty`
would lead to performance issues:
{{{
import Text.PrettyPrint
import Data.List
import Criterion.Main
f_left :: Int -> Doc
f_left n = foldl' (<>) empty (map (text . show) [10001..10000+n])
f_right :: Int -> Doc
f_right n = foldr (<>) empty (map (text . show) [10001..10000+n])
main =
defaultMain $
[ bench "left" $ nf (length . render . f_left) 10000
, bench "right" $ nf (length . render . f_right) 10000
, bench "left20k" $ nf (length . render . f_left) 20000
, bench "right20k" $ nf (length . render . f_right) 20000
, bench "left30k" $ nf (length . render . f_left) 30000
, bench "right30k" $ nf (length . render . f_right) 30000
]
}}}
Results (lower numbers are better):
{{{
Iterations
_10K__________20K__________30K________
Left 10.1 (0.5) 24.4 (0.6) 40.0 (1.3)
Right 8.9 (0.2) 22.7 (3.1) 31.2 (4.6)
Format: runtime (stddev) all in milliseconds
}}}
So switching to right-associativity may actually increase performance
slightly. Scaling doesn't seem to be quite linear, but that could be due
to cache effects or suchlike; and it's also outside the scope of this
proposal.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3339#comment:22>
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