gistfile1.hs

import Text.ParserCombinators.Parsec

data RailsLogSummaryLine = RailsLogSummaryLine {
  requestStatus                ::  String,
  requestTotalTime             ::  String,
  requestDbTime                ::  String,
  requestViewTime              ::  String
} deriving (Show, Ord, Eq)

data RailsLogParsingResult = Fail String
  | Summary RailsLogSummaryLine

plainValue :: Parser String
plainValue = many1 (noneOf " ()")

timeValue :: Parser String
timeValue = many1 (noneOf "ms")

bracketedValue = do
    char '('
    plainValue
    space
    viewTime <- timeValue
    plainValue
    space
    char '|'
    space
    plainValue
    space
    dbTime <- timeValue
    plainValue
    char ')'
    return (viewTime, dbTime)

summaryLogLine :: Parser RailsLogSummaryLine
summaryLogLine = do
  plainValue
  space
  status <- plainValue
  space 
  plainValue
  space
  plainValue
  space
  totalTime <- timeValue
  plainValue
  space
  viewAndRenderTime <- bracketedValue
  return $ RailsLogSummaryLine status totalTime (fst viewAndRenderTime) (snd viewAndRenderTime)

parseSummaryLine inputLine = case parse summaryLogLine "(summary)" inputLine of
    Left  err -> Fail $ show err
    Right res -> Summary res

clearFailedParses [] result = result
clearFailedParses (h:hs) result = 
  case h of
    Summary smr -> clearFailedParses hs (show smr : result)
    Fail err    -> clearFailedParses hs result

clearFailedParses' [] result = result
clearFailedParses' (h:hs) result = 
  case h of
    Summary smr -> clearFailedParses' hs (smr : result)
    Fail err    -> clearFailedParses' hs result

logEntryTimes e = 
  case e of
    RailsLogSummaryLine _ total view db -> [ (read total :: Float), (read view :: Float), (read db :: Float)]

avgTimes [] (total:view:db) = [show total, show view, show db] 
avgTimes (h:hs) result =
  let total = ((result !! 0) + ((logEntryTimes h) !! 0)) / 2.0 in
    let view = ((result !! 1) + ((logEntryTimes h) !! 1)) / 2.0 in
      let db = ((result !! 2) + ((logEntryTimes h) !! 2)) / 2.0 in
        avgTimes hs [ total, view, db ]

main = do 
  file <- readFile "production.log"
  let logLines = lines file in
    let parseResult = map parseSummaryLine logLines in
      let results = clearFailedParses parseResult [] in
        let results' = clearFailedParses' parseResult [] in
          let vals = avgTimes results' [1.0, 1.0, 1.0] in
            mapM putStrLn vals