Re: [Haskell-cafe] Undocumented cost-centres (.\) using auto-all, and SCC pragma not being honored

16 Feb 2012


      On Wed, Feb 15, 2012 at 9:51 PM, Thomas Schilling
wrote:
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On 15 February 2012 16:17, Dan Maftei  wrote:
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1 When profiling my code with -auto-all, my .prof file names some
sub-expressions with a backslash. Cf. below. What are these?
...
e_step
      e_step.ewords
      e_step.\
       e_step.\.\
        e_step.update_counts
      e_step.fwords
Yup, those are anonymous functions.
Thank you. I'm still curious why other (named) expressions don't show up.
I'm running the profiler again now and they DO. Odd...
...
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2. A related question: I tried using the SCC pragma instead of auto-all.
I added it to all seven expressions inside the let, and to the nested
folds. However, only two showed up in the .prof file! How come?
It would be helpful if you pasted the code.  I think SCC pragmas
around lambdas get ignored and you should put them inside.  (It may be
the other way around, though.)
God this is embarrassing... it's horrible code, I don't know monads yet
and EM makes more sense in an imperative paradigm, but I felt like pushing
the envelope and failed miserably lol. Anyways:

e_step ttable (fsentence, esentence) (counts, totals) =
  let
    ewords = {-# SCC "ewords" -#} T.words esentence
    fwords = {-# SCC "fwords" -#} T.words fsentence
    -- calculate s-total(e) map

    sTotal = {-# SCC "sTotal" -#} foldr (update_sTotal fwords) M.empty
ewords
    update_sTotal fwords e sTotal = {-# SCC "update_sTotal" -#}
      foldr (\f sTotal ->
              M.insertWith (+) e (getProb f e ttable) sTotal)
      sTotal fwords
    -- helpers for updating counts

    update_counts counts e f sTotal = {-# SCC "update_counts" -#}
      let !adding = (getProb f e ttable) / (sTotal M.! e)
      in M.insertWith (M.unionWith (+)) f (M.singleton e adding) counts
    update_totals totals e f sTotal = {-# SCC "update_totals" -#}
      let !adding = (getProb f e ttable) / (sTotal M.! e)
      in M.insertWith' (+) f adding totals
  in {-# SCC "folds" -#}
   -- update counts by iterating over words

   foldr (\f (!counts, !totals) ->
           foldr (\e (!counts, !totals) ->
                   let !newCounts = update_counts counts e f sTotal
                       !newTotals = update_totals totals e f sTotal
                   in (newCounts, newTotals))
           (counts, totals) ewords)
   (counts, totals) fwords