_Why Yown Is Funny So You Can Laugh Too | Hacker News Reader

_Why Yown Is Funny So You Can Laugh Too

discoveringio.blogspot.com

20 pointsphaedrus10 comments

I don't think I can read Io that well, but this doesn't seem like a very unique trick; Ruby has method_missing (like the first commenter mentions) and Python has __getattr__. Is there something else I'm not seeing in there?

And Perl has AUTOLOAD. However the difference to these is that Io is being lazy in the examples provided in the blog post. NB. its all just messages and no commas (ie. no args).

ref: "Lazy Bricks, Lazy Mortar" by why - WayBackMachine link: http://web.archive.org/web/20080430135919/http://hackety.org...

BTW here is a quick & dirty example of Io laziness and shows what can be done without forward (did-not-understand/method_missing/__getattr__/AUTOLOAD):

    Hash := Object clone do (
        with := method (
            hash := Map clone
            call message arguments foreach (arg,
                # arg = k(v)  for eg. t(0)
                k := arg name
                v := arg argAt(0) asString
                hash atPut (k, doString (v))
            )
            hash
        )
    )


    h  := Hash with (t(0), f(1+1), with("hello"), writeln("not writeln!"))
    h2 := Hash with (t(100), f("hello" asUppercase), at("my at"), atPut("my atPut"))

Above lazily goes through the Hash with() building the key/value pairs without ever running methods/functions with, writeln, at, atPut and simply takes the method/func name and evaluates its argument into a key/value pair:

    h  at ("writeln") println  # => "not writeln!"
    h  at ("f") println        # => 2
    h2 at ("f") println        # => "HELLO"

This is the reflection alternative the author is referring to in his post.

Personally I thought Yown was a work in progress and just _why dabbling with Io rather than a practical joke.

I think Yown got me more interested in playing with Io than anything else. However the Builder is limited (because everything gets converted to a html tag). There are more complete HTML builders for Io on github.

Bruce Tate also provides a nice example of a HTML builder in *Seven languages in 7 weeks". Below is my slightly amended version of it:

    Builder := Object clone
    Builder forward := method ( 
        write ("<", call message name, ">") 
        call message arguments foreach (arg, 
            content := self doMessage (arg);
            if (content type == "Sequence" or content type == "Number", write(content))
        )
        write ("</", call message name, ">")
    )

    Builder do (
        html (
            h1 ("header")
            div (
                p ("paragraph", b ("bold"), "more text")
                ul (list(1,2,3) foreach (n, li (n)))
            )
        )
    )

Sort of tooting my own horn here, but here's an HTML builder in the language I'm working on: http://gist.github.com/513228 (Example usage and output at the bottom.) I write these a lot to test a language's flexibility.

Seems like Io's "forward" is a lot like "did-not-understand" (and similar mechanisms in Ruby/etc. languages), but it takes priority over messages that would've otherwise been understood.

Thats OK, toot away! But I'll toot my own as well then :) http://github.com/draegtun/builder

Mine (in perl) is more akin to Ruby's Builder by Jim Weirich (http://builder.rubyforge.org/) than out and out HTML builder.

BTW, other HTML builders have been mentioned on HN before: http://news.ycombinator.com/item?id=1518096

Neat! They're pretty fun to make; I write them a lot to test a language's flexibility.

Seems like Io's "forward" is a lot like "did-not-understand" (and similar mechanisms in Ruby/etc. languages), but it takes priority over messages that would've otherwise been understood.

Yes its same as did-not-understand/method_missing/__getattr__/AUTOLOAD but no it doesn't take priority over other defined messages.

For eg, If I change the first line in my code above to:

    Builder := Object do (
        foo := method (arg, write (arg))
    )

And do:

    Builder do (
        h1 (
            foo ("Foo here!")
            p ("paragraph")
        )
    )

I get a untagged "Foo Here!":

    <h1>Foo here!<p>paragraph</p></h1>

Ah, ok - I misinterpreted the article.

Actually, the article seems to be wrong? It seems to imply that this shouldn't work:

    Io> x := Object clone do( forward := 0; a := 1 )
    ==>  Object_0x1003a2e90:
      a                = 1
      forward          = 0

    Io> x a
    ==> 1
    Io> x b
    ==> 0
    Io> x b := 2
    ==> 2
    Io> x b
    ==> 2

(paragraph: There are some things you should know about forward(). It's very powerful. Too powerful. [...])

Not sure what the article is referring to there? As far as I know you would have to amend the objects protos or overwrite the setSlot message (which := is an alias for) to change this behaviour.

The documentation clearly states for forward that: If an object doesn't respond to a message, it will invoke its "forward" method if it has one.

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