On Wednesday, January 11, 2017 at 4:23:28 PM UTC-6, david swift wrote:
>
> Been working on a tiny snippet of code related to multimethods (something
> I've never quite wrapped my head around) and when it comes to the
> dispatching of the function I'm confused by the order in which I've to pass
> the arguments in as it seems to go against all common sense.
>
> To show what I am trying to do (to begin with); ignoring name
> conflictions. Without implementing algorithm details I supply a simple
> string for ease.
> (defmulti transform (fn [language data] language))
>
> (defmethod transform :html
> [_ data]
> (str data " will be transformed into html")))
>
^ extra ) at the end there fyi
>
>
> (defmethod transform :java-fx
> [_ data]
> (str data " will be transformed into javafx"))
>
> What I would expect from this outcome would be to do the following on
> dispatch
> (transform :html "some data") => "some data will be transformed into html"
>
This is what I see and that looks right to me. I suspect you somehow have
old method impls in your repl state. You should try with a fresh repl.
>
> But instead the output I actually get ends up being
> "some data"
> which I assume to be the default for mulitmethods to return the data
> value. Though if I were to instead to change the order of the arguments
> like so.
>
> (transform "some data" :html) => "some data will be transformed into html"
> The expect outcome I wanted but not with the "correct" argument order I
> was expecting, and to also note this (for me) prevents me from having more
> than one argument and dispatch case.
>
I get
IllegalArgumentException No method in multimethod 'transform' for dispatch
value: some data clojure.lang.MultiFn.getFn (MultiFn.java:156)
I know that I can do this approach
> (transform {:language :html} "some data")
> and it would work in the correct order but it's extra data I'm looking to
> avoid for the sake of correct argument order
>
> Ideally I would of like the code to look something like below
> (defmulti transform :language)
>
> (defmethod transform :html
> [data]
> (str data " will be transformed into html"))
>
> (defmethod transform :java-fx
> [data]
> (str data " will be transformed into javafx"))
>
> I'd be grateful if someone could give me some simple examples to go by
> that work by keyword dispatch that isn't foobaz, thank you :)
>
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