From: Julian Leviston <julian@...>
Date: 2009-02-09T11:50:10+09:00
Subject: Re: ruby interpreter written in ruby..

I don't think a measure such as that is useful for anything much. IMHO  
you'd want a language written in itself so you could understand it  
better at a lower level: pedagogy.

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On 09/02/2009, at 9:42 AM, John Carter <john.carter@tait.co.nz> wrote:

> On Sun, 8 Feb 2009, Dylan Evans wrote:
>
>>> I was wondering is there a ruby written ruby interpreter  
>>> available? somehow
>>> i`d like to be able to read the interpreter source.
>
> Hokay, so this is at the trivial "HEY! You Cheated!!" level... but
> it's still useful...
>
> ri 'Kernel#eval'
> ------------------------------------------------------------  
> Kernel#eval
>     eval(string [, binding [, filename [,lineno]]])  => obj
> --- 
> ---------------------------------------------------------------------
>     Evaluates the Ruby expression(s) in _string_. If _binding_ is
>     given, the evaluation is performed in its context. The binding may
>     be a +Binding+ object or a +Proc+ object. If the optional
>     _filename_ and _lineno_ parameters are present, they will be used
>     when reporting syntax errors.
>
>        def getBinding(str)
>          return binding
>        end
>        str = "hello"
>        eval "str + ' Fred'"                      #=> "hello Fred"
>        eval "str + ' Fred'", getBinding("bye")   #=> "bye Fred"
>
>
>> Why would you want a ruby interpreter written in ruby?
>
> Actually the original poster asked a very intelligent question.
>
> Why would you want such a thing?
>
> It's a _very_ effective measure of the simplicity and expressiveness
> combined of the language.
>
> For example, here is a minimal (non-trivial) Joy0 interpeter written
> in Joy0 that will interpret itself.
> Source http://www.latrobe.edu.au/philosophy/phimvt/joy/jp-joyjoy.html
>
> joy0  ==
>    [ [ [ joy0          body            joy0     ]
>        [ []                                     ]
>        [ pop           pop             pop      ]
>        [ cons          pop             cons     ]
>        [ opcase        pop             opcase   ]
>        [ body          pop             body     ]
>        [ i             pop             joy0     ]
>        [ step          pop [joy0] cons step     ]
>        [               [] cons         i        ] ]
>      opcase
>      i ]
>    step
>
>
> Yup. That was it. All of it.
>
> Says something very very powerful about the simplicity of the Joy
> language.
>
> I'll admit I learnt several things about the language when I read that
> close enough to understand it.
>
> I bet you'd have a good few "Aha!" moments if you could do the same
> with Ruby.
>
> Conversely, if you could strip Ruby to a Ruby0 essence in which you
> could easily write a ruby0 in ruby0 interpreter... you'd learn what
> was the essence of the language and what was sugar.
>
>
> John Carter                             Phone : (64)(3) 358 6639
> Tait Electronics                        Fax   : (64)(3) 359 4632
> PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
> New Zealand
>
>