[plt-scheme] "appending" to classes rather than extending

Yeah, seems to just work in Ruby (see code below).

It seems strange to me that I can't just "re-export" the definition of foo:

(define-unit extension-unit%
  (import sig^)
  (export sig^)

  (define (bar)
    "appended bar impl"))

But unfortunately? it gives me:

define-unit: import foo is exported in: (define-unit extension-unit%
(import sig^) (export sig^) (define (bar) "appended bar impl"))

Here's that Ruby code:

class Foo
  def initialize(count)
    @count = count
  end

  def bar
    if @count <= 0
      print "done\n"
    else
      print "bar\n"
      @count = @count - 1
      baz
    end
  end
end

class Foo
  def baz
    if @count <= 0
      print "done\n"
    else
      print "baz\n"
      @count = @count - 1
      bar
    end
  end
end

Foo.new(4).bar =>
bar
baz
bar
baz
done




On Wed, Mar 5, 2008 at 2:25 PM, Matthias Felleisen <matthias at ccs.neu.edu> wrote:
>
>  Yes. Since you want to talk about both base:bar and extension:bar in
>  one unit, I don't see how to do it w/o some name shuffling.
>
>  BTW, happens if the foo and bar methods are (mutually) recursive in
>  Ruby. Does this "just work"?
>
>  -- Matthias
>
>
>
>
>
>
>
>
>  On Mar 5, 2008, at 4:51 PM, Rob Hunter wrote:
>
>  > Thanks, Matthias.  Below is my interpretation of your suggestion of
>  > using units to get this effect.  The only parts of my solution that I
>  > don't like is how I had to prefix the import in extension-unit%, and
>  > how I had to explicitly define foo for export even though I didn't
>  > want to override it.  Surely there's a way to avoid both of those
>  > things...
>  >
>  > Thanks,
>  > Rob
>  >
>  > (define-signature sig^ (foo bar))
>  >
>  > (define-unit base-unit%
>  >   (import)
>  >   (export sig^)
>  >
>  >   (define (foo)
>  >     "foo base impl")
>  >
>  >   (define (bar)
>  >     "bar base impl"))
>  >
>  > (define-unit extension-unit%
>  >   (import (prefix base: sig^))
>  >   (export sig^)
>  >
>  >   (define foo base:foo)
>  >
>  >   (define (bar)
>  >     "appended bar impl"))
>  >
>  > (define-compound-unit merged-unit%
>  >   (import)
>  >   (export RESULT)
>  >   (link [((BASE : sig^)) base-unit%]
>  >         [((RESULT : sig^)) extension-unit% BASE]))
>  >
>  >
>  > REPL interaction:
>  >> (define-values/invoke-unit merged-unit% (import) (export sig^))
>  >> (foo)
>  > "foo base impl"
>  >> (bar)
>  > "appended bar impl"
>  >
>  >
>  >
>  >
>  >
>  >
>  > On Wed, Mar 5, 2008 at 12:58 PM, Matthias Felleisen
>  > <matthias at ccs.neu.edu> wrote:
>  >>
>  >>  You could achieve this kind of effect (via units) but re-definitions
>  >>  in a module (and that's what this boils down to) of the same name
>  >> are
>  >>  frowned upon in Scheme. -- Matthias
>  >>
>  >>  P.S. Re-definitions at the top-level have been around for a LONG
>  >> time
>  >>  and there is a reason why Schemers are moving away from that
>  >> approach.
>  >>
>  >>
>  >>
>  >>  On Mar 5, 2008, at 3:41 PM, Rob Hunter wrote:
>  >>
>  >>> Hi all,
>  >>>
>  >>> I'm looking to be able to append a few methods to a class.  In
>  >>> Ruby, I
>  >>> can do something like this:
>  >>>
>  >>> class Foo
>  >>>   def bar
>  >>>     ...
>  >>>   end
>  >>>   ...
>  >>> end
>  >>>
>  >>> class Foo
>  >>>   def baz
>  >>>     ...
>  >>>   end
>  >>> end
>  >>>
>  >>> and both bar and baz will be a part of Foo (these two class defs
>  >>> could
>  >>> be in the same file, or in two different files that are both
>  >>> loaded).
>  >>> Anything like this in the PLT Scheme class system?
>  >>>
>  >>> Thanks,
>  >>> Rob
>  >>> _________________________________________________
>  >>>   For list-related administrative tasks:
>  >>>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>  >>
>  >>
>
>