April 2008 - Glasgow-haskell-users

ANN: prof2dot, a graphical profiling tool
by Gregory Wright 02 Apr '08

02 Apr '08

I am pleased to announce the first release of prof2dot, a graphical profiling tool for use with GHC. While GHC has in the past worked with graphical profiling tools, they have been heavyweight and/or proprietary. Prof2dot is a simple tool for converting profiling information into a graphical format, released under a BSD3 license. It is simple because it offloads all of the work of rendering the graph onto Graphviz. So you need to install the Graphviz tools in order to use it. The program is a filter that takes the profiling output generated by running a GHC-compiled program with the "+RTS -px -RTS" option and turns it into a dot file. (The "dot" format is a textual representation of a directed or undirected graph.) The dot file can rendered in any format supported by Graphviz's dot program, and the file itself can be post-processed or edited to adjust the layout. Features of prof2dot: * display either the call graph (default) or the call tree, * colorize by cost center count, time or allocations, * group cost centers in the same module. Prof2dot installs as a typical caballized application. Running "prof2dot -?" from the command line will give a short summary of how to use the program and its options. Rendering very large graphs can exceed the internal resource limits of dot. You may have to compile your own version of the Graphviz tools with higher limits to handle these cases. A example of a colorized profile of a medium sized project is shown on our company's web site: http://antiope.com/downloads.html. Click on the small image to download a pdf of the complete profile graph. Prof2dot is available from hackage or the link given above. -Greg

2 2

ghc fails to find the right instance
by Joachim Breitner 01 Apr '08

01 Apr '08

Hi, I was told on #haskell that I should bring this up here, to ask whether this is a bug in ghc6 or otherwise explain this to me. I’m trying to write the function "addd" which takes an arbitrary number of Integer arguments and returns the sum. This code works: -- Try 1 class More a where more ::Integer -> a instance (More a, Integral i) => More (i -> a) where more v1 v2 = more (v1 + toInteger v2) instance More Integer where more v = v addd :: More a => a addd = more 0 printI :: Integer -> IO () printI = print main = do printI $ addd printI $ addd 1 printI $ addd 1 2 printI $ addd 1 2 3 -- SNIP But when I try to use a concret type (Integer) instead of the (Integral i =>) condition (which should make the program more concrete, I’d say) and write the following instance: -- Try 2 (changed lines of code) instance More a => More (Integer -> a) where more v1 v2 = more (v1 + v2) -- SNIP I get this error: test.hs:4:0: Illegal instance declaration for `More (Integer -> a)' (All instance types must be of the form (T a1 ... an) where a1 ... an are distinct type *variables* Use -XFlexibleInstances if you want to disable this.) In the instance declaration for `More (Integer -> a)' Failed, modules loaded: none. Well, I add {-# LANGUAGE FlexibleInstances #-} and get this error for the line "printI $ addd 1" (and similar errors for the other following addd lines): test.hs:19:17: No instance for (More (t -> Integer)) arising from a use of `addd' at test.hs:19:17-22 Possible fix: add an instance declaration for (More (t -> Integer)) In the second argument of `($)', namely `addd 1' In the expression: printI $ addd 1 In a 'do' expression: printI $ addd 1 And this is the point where I’m lost and would like to ask for hints what this means. Thanks, Joachim -- Joachim "nomeata" Breitner mail: mail(a)joachim-breitner.de | ICQ# 74513189 | GPG-Key: 4743206C JID: nomeata(a)joachim-breitner.de | http://www.joachim-breitner.de/ Debian Developer: nomeata(a)debian.org

2 3

simple CSE?
by Conal Elliott 01 Apr '08

01 Apr '08

I'd like to know if it's possible to get GHC to perform some simple CSE for function-level programming. Here's a simple example: liftA2 (*) sin sin :: Double -> Double which inlines and simplifies to \ t -> sin t * sin t A more realistic, equivalent, example: let b = sin <$> id in liftA2 (*) b b Can GHC be nudged into computing 'sin t' once rather than twice? Thanks, - Conal

4 3

patch-applied messages
by Christian Maeder 01 Apr '08

01 Apr '08

(resent this request for cvs-ghc(a)haskell.org to glasgow-haskell-users) Hi, could the actual change-diff of patches also be posted via this list (or a web-link to the change)? I think this was the case with the old cvs repository. This would teach a bit Haskell programming and how to write expressive log messages. Currently I never look up changes, although the log messages make me curious sometimes. (I rarely use darcs.) Cheers Christian This is just an example (with an uninteresting diff) > Tue Mar 25 17:49:32 PDT 2008 Ian Lynagh <igloo(a)earth.li> > * Remove a redundant type sig > > M ./compiler/ghci/InteractiveUI.hs -1

1 1