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"
> <[email protected]<javascript:>>
> 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
>>
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