;; Better yet...
(if (or (and (multi? graph) (not= 2 (count edge)))
(and (looped? graph) (not (distinct? edge))))
graph
(let [e (if (directed? edge) (vec edge) (set edge))]
(update-in graph [:edges] conj e))))
On Thu, Sep 5, 2013 at 2:22 PM, Alex Baranosky <
[email protected]> wrote:
> 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 <
> [email protected]> 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" <[email protected]>
>>> 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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