I'd just use a cond to flatten a nested if. That's usually all you need, imo.
On Thu, Sep 5, 2013 at 1:07 PM, Bruno Kim Medeiros Cesar < brunokim...@gmail.com> wrote: > Thanks for your suggestion, didn't know about that! One of the things that > made someone say that "Clojure looks like a language from the near future". > However, I'm having a hard time using it with its full power. Could you > recommend any other resource, besides the overview page on github, to learn > pattern matching? Maybe a project that uses them? > > For the record, my code uses a simple truth table now: > > > (defn add-edge > ([g v1 v2 & vs] (add-edge g (concat [v1 v2] vs))) > ([g edge] > (let [two? (= 2 (count edge)) > dist? (apply distinct? edge) > e (match [(hyper? g) (looped? g)] ; e will be nil if edge is > invalid for this graph > [false false] (when (and two? dist?) edge) > [false true ] (when two? edge) > [true false] (when dist? edge) > [true true ] edge] > (if e > (update-in g [:edges] conj (if (directed? g) (vec e) (set e))) > g)))) > > On Wednesday, September 4, 2013 7:07:06 PM UTC-3, Leonardo Borges wrote: > >> You could use pattern matching with core.match >> On 05/09/2013 6:57 AM, "Bruno Kim Medeiros Cesar" <bruno...@gmail.com> >> wrote: >> >>> I'm writing (another) basic graph library, and would like to treat >>> inputs depending on the type of the graph. A graph can be >>> >>> - Directed, in which case edges are vectors. Otherwise, edges are >>> sets; >>> - Looped, allowing edges from a node to itself; >>> - Pseudo (or multi), allowing multiples edges between the same >>> endpoints; and >>> - Hyper, allowing edges with more than two vertices. >>> >>> To illustrate better these characteristics you can think of a scientific >>> publication network as a directed, looped, pseudo-hypergraph. Vertices are >>> authors, and edges are articles containing multiple researchers (hyper) who >>> can publish alone (looped). There are multiple articles between the same >>> researchers (pseudo) and in some contexts author order matters (directed). >>> >>> Now, I've created a flowchart <http://imgur.com/IdgsGFG> to decide if >>> an edge should be conjed in a graph :edges entry, that leads to the >>> following straightforward function: >>> (defn add-edge >>> ([graph v1 v2 & vs] (add-edge graph (concat [v1 v2] vs))) >>> ([graph edge] >>> (if (and (multi? graph) (not= 2 (count edge))) >>> graph >>> (if (and (looped? graph) (not (distinct? edge))) >>> graph >>> (let [e (if (directed? edge) (vec edge) (set edge))] >>> (update-in graph [:edges] conj e)))))) >>> >>> That looks ugly and a pattern that could propagate in a codebase. So I >>> tried to factor out multimethods from it, and ended with the following: >>> >>> (defmulti ^:private add-edge0 (fn [g e] (hyper? g))) >>> (defmulti ^:private add-edge1 (fn [g e] (looped? g))) >>> (defmulti ^:private add-edge2 (fn [g e] (directed? g))) >>> (defn ^:private add-edge3 [g e] >>> (update-in g [:edges] conj e)) >>> >>> (defmethod add-edge0 :hyper [g e] (add-edge1 g e)) >>> (defmethod add-edge0 :default [g e] (if (= 2 (count e)) >>> ** (add-edge1 g e) >>> ** g)) >>> (defmethod add-edge1 :looped [g e] (add-edge2 g e)) >>> (defmethod add-edge1 :default [g e] (if (distinct? e) >>> ** (add-edge2 g e) >>> ** g)) >>> (defmethod add-edge2 :directed [g e] (add-edge3 g (vec e))) >>> (defmethod add-edge2 :default [g e] (add-edge3 g (set e))) >>> >>> (defn add-edge >>> ([g v1 v2 & vs] (add-edge g (concat [v1 v2] vs))) >>> ([g edge] (add-edge0 g edge))) >>> >>> That doesn't look much better, as the amount of boilerplate increased, >>> but at least the concerns for each type are separated. >>> >>> Do you have any suggestions on how to improve this design? Thanks for >>> any consideration! >>> >>> Bruno Kim Medeiros Cesar >>> Engenheiro de Computação >>> Pesquisador em Redes Complexas >>> www.brunokim.com.br >>> >>> -- >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Clojure" group. >>> To post to this group, send email to clo...@googlegroups.com >>> >>> Note that posts from new members are moderated - please be patient with >>> your first post. >>> To unsubscribe from this group, send email to >>> clojure+u...@**googlegroups.com >>> >>> For more options, visit this group at >>> http://groups.google.com/**group/clojure?hl=en<http://groups.google.com/group/clojure?hl=en> >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "Clojure" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to clojure+u...@**googlegroups.com. >>> >>> For more options, visit >>> https://groups.google.com/**groups/opt_out<https://groups.google.com/groups/opt_out> >>> . >>> >> -- > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > --- > You received this message because you are subscribed to the Google Groups > "Clojure" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to clojure+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/groups/opt_out. > -- -- You received this message because you are subscribed to the Google Groups "Clojure" group. 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