PerfT is a monad transformer designed to collect performance information. The transformer can be used to add performance measurent to an existing code base using Measures.

For example, here's some code doing some cheesey stuff:

  -- prior to Perfification
  result <- do
      txt <- readFile "examples/examples.hs"
      let n = Text.length txt
      let x = foldl' (+) 0 [1..n]
      putStrLn $ "sum of one to number of characters is: " <>
          (show x :: Text)
      pure (n, x)

And here's the code after Perfification, measuring performance of the components.

  (result', ms) <- runPerfT $ do
          txt <- perf "file read" cycles $ readFile "examples/examples.hs"
          n <- perf "length" cycles $ pure (Text.length txt)
          x <- perf "sum" cycles $ pure (foldl' (+) 0 [1..n])
          perf "print to screen" cycles $
              putStrLn $ "sum of one to number of characters is: " <>
              (show x :: Text)
          pure (n, x)

Running the code produces a tuple of the original computation results, and a Map of performance measurements that were specified. Indicative results:

file read                               4.92e5 cycles
length                                  1.60e6 cycles
print to screen                         1.06e5 cycles
sum                                     8.12e3 cycles