Thanks Mark for you reply. Well I realized we can do that .. but I feel it
would be more expressive and readable if I could do the wild-card like
pattern matching when I am defining the method.
Sunil.
On Mon, Sep 6, 2010 at 9:25 AM, Mark Rathwell <mark.rathw...@gmail.com>wrote:
>
> You can add essentially one more level of indirection to your dispatch
> function logic and return an integer (or string or whatever) and match on
> that. So, with your example, when you want "method1" called, return 1 from
> the dispatch function, when you want "method2" return 2, you get the idea:
>
> (defmulti foo mclass)
> (defmethod foo 1 [s] (str "I'm method 1"))
> (defmethod foo 2 [s] (str "I'm method 2"))
> ...
>
> Is this what you are getting at?
>
> - Mark
>
> On Sun, Sep 5, 2010 at 8:50 PM, Sunil S Nandihalli <
> sunil.nandiha...@gmail.com> wrote:
>
>> Hello everybody,
>> It is awesome that we can specify our own dispatch functions and
>> corresponding values.. However, I feel we should also have control over the
>> functions that is used to match the value of the dispatch function with that
>> of the one specified in the defmethod.
>> For instance if my dispatch function is
>>
>> *(defn mclass [s]*
>> * (vec (reverse (loop [ret '() val s]*
>> * (if (coll? val)*
>> * (recur (cons (class val) ret) (first val))*
>> * (cons (class val) ret))))))*
>>
>> which basically tries to give a list of all the nested types of a value.
>> If a value is a collection, then all its elements are of same type.
>> so the above function when applied on .. let us say
>>
>> *(mclass #{'([1 2] [3 4])*
>> * '([5 6] [7 8])})*
>>
>> the return value would be
>>
>> *[clojure.lang.PersistentHashSet clojure.lang.PersistentList
>> clojure.lang.PersistentVector java.lang.Integer]*
>>
>> I would like to despatch based on some pattern of the return value of my
>> dispatch function *mclass*
>> *
>> *
>> For instance I would like to say something like when the second element of
>> return value of the dispatch function is *PersistentList call method1
>> and call method2 when say the first element is PersistentList and second
>> element is say PersistentHashSet and call method3 for some other
>> pattern. Basically a general pattern matching .. So if only I could have a
>> way of changing how the equality for the purpose of dispatching behaves ..
>> it would be wonderful. We could either do this or we could change the
>> dispatch-val to a dispatch-function with a single argument .. Or is there a
>> way to already do this?*
>>
>> In short is it possible to do a generic pattern-matching during dispatch
>> in multimethods?
>>
>> Sunil.
>>
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