| Andrew Cooke | Contents | Latest | RSS | Twitter | Previous | Next

C[omp]ute

Welcome to my blog, which was once a mailing list of the same name and is still generated by mail. Please reply via the "comment" links.

Always interested in offers/projects/new ideas. Eclectic experience in fields like: numerical computing; Python web; Java enterprise; functional languages; GPGPU; SQL databases; etc. Based in Santiago, Chile; telecommute worldwide. CV; email.

Personal Projects

Lepl parser for Python.

Colorless Green.

Photography around Santiago.

SVG experiment.

Professional Portfolio

Calibration of seismometers.

Data access via web services.

Cache rewrite.

Extending OpenSSH.

C-ORM: docs, API.

Last 100 entries

Even; Cherry Jam; Lebanese Writer Amin Maalouf; Learning From Trump; Chinese Writer Hu Fayun; C++ - it's the language of the future; And; Apricot Jam; Also; Excellent Article on USA Politics; Oh Metafilter; Prejudice Against The Rurals; Also, Zizek; Trump; Why Trump Won; Doxygen + Latex on CentOS 6; SMASH - Solve 5 Biggest Problems in Physics; Good article on racism, brexit, and social divides; Grandaddy are back!; Consciousness From Max Entropy; Democrats; Harvard Will Fix Black Poverty; Modelling Bicycle Wheels; Amusing Polling Outlier; If Labour keeps telling working class people...; Populism and Choice; Books on Defeat; Enrique Ferrari - Argentine Author; Transcript of German Scientists on Learning of Hiroshima; Calvert Journal; Owen Jones on Twitter; Possible Japanese Authors; Complex American Literature; Chutney v5; Weird Componentized Virus; Interesting Argentinian Author - Antonio Di Benedetto; Useful Thread on MetaPhysics; RAND on fighting online anarchy (2001); NSA Hacked; Very Good LRB Article on Brexit; Nussbaum on Anger; Tasting; Apple + Kiwi Jam; Hit Me; Sudoku - CSP + Chaos; Recycling Electronics In Santiago; Vector Displays in OpenGL; And Anti-Aliased; OpenGL - Render via Intermediate Texture; And Garmin Connect; Using Garmin Forerunner 230 With Linux; (Beating Dead Horse) StackOverflow; Current State of Justice in China; Axiom of Determinacy; Ewww; Fee Chaos Book; Course on Differential Geometry; Okay, but...; Sparse Matrices, Deep Learning; Sounds Bad; Applebaum Rape; Tomato Chutney v4; Have to add...; Culturally Liberal and Nothing More; Weird Finite / Infinite Result; Your diamond is a beaten up mess; Maths Books; Good Bike Route from Providencia / Las Condes to Panul; Iain Pears (Author of Complex Plots); Plum Jam; Excellent; More Recently; For a moment I forgot StackOverflow sucked; A Few Weeks On...; Chilean Book Recommendations; How To Write Shared Libraries; Jenny Erpenbeck (Author); Dijkstra, Coins, Tables; Python libraries error on OpenSuse; Deserving Trump; And Smugness; McCloskey Economics Trilogy; cmocka - Mocks for C; Concept Creep (Americans); Futhark - OpenCL Language; Moved / Gone; Fan and USB issues; Burgers in Santiago; The Origin of Icosahedral Symmetry in Viruses; autoenum on PyPI; Jars Explains; Tomato Chutney v3; REST; US Elections and Gender: 24 Point Swing; PPPoE on OpenSuse Leap 42.1; SuperMicro X10SDV-TLN4F/F with Opensuse Leap 42.1; Big Data AI Could Be Very Bad Indeed....; Cornering; Postcapitalism (Paul Mason); Black Science Fiction; Git is not a CDN

© 2006-2015 Andrew Cooke (site) / post authors (content).

Topological Sort in Erlang

From: "andrew cooke" <andrew@...>

Date: Thu, 19 Apr 2007 01:47:25 -0400 (CLT)

This uses the monad library described at
http://www.acooke.org/cute/MonadsinEr0.html

Some variables/functions:
- gr_get_out returns a list of edges for the named node in the graph
- repeat_app is repeat using lists:append for joining
- drop pulls the final result out of the monad
- the initial function bootstraps with an initial set of edges

Personally, I am surprised how clean this is.  When I wrote the monad code
I hadn't even considered tree-like program flow.  Note that Graph is
actually constant throughout.

Andrew

top_sort(Name, Graph) ->
    drop([], [],
      repeat_app(
        fun top_sort/1,
        ({gr_get_out(Name, Graph), gb_sets:new(), Graph}))).

top_sort({[], _, _}) -> fail;
top_sort({[Head|Tail], Visited, Graph}) ->
    case gb_sets:is_element(Head, Visited) of
        % already visited - do nothing
        true -> {empty, {Tail, Visited, Graph}};
        % visit all children then add this node to the list
        _ -> Visited2 = gb_sets:add_element(Head, Visited),
             case repeat_app(fun top_sort/1,
                             {gr_get_out(Head, Graph), Visited2, Graph}) of
                 % this shouldn't happen
                 fail -> fail;
                 % no children, so we are at the end of a chain
                 {empty, {_, Visited3, Graph2}} ->
                     {[Head], {Tail, Visited3, Graph2}};
                 % append this node to the sorted children and continue
                 {Sorted, {_, Visited3, Graph2}} ->
                     {[Head|Sorted], {Tail, Visited3, Graph2}}
             end
    end.

Comment on this post