From: ptkwt@... (Phil Tomson)
Date: 2004-04-03T17:54:23+09:00
Subject: Re: Learning Ruby, was a C geek...

In article <Pine.LNX.4.44.0404021817070.6456-100000@localhost.localdomain>,
Nicholas Paul Johnson  <nickjohnson@virginia.edu> wrote:
>Hello all,
>
>As I'm learning Ruby, I've decided to write a few programs in Ruby to get
>a feel for the language.
>
>I've been a C programmer for a long time.  As such, I worry that I'm
>thinking too much like a C programmer, and not like a Ruby programmer...
>
>My first attempt has been an emulator for a cs-toy processor called IBCM 
>(itty-bitty computing machine).  Its spec (only 5 pages) is available at: 
>http://www.cs.virginia.edu/~cs216/notes/ibcm-poo.pdf
>
>I've written it, and it works correctly when compared to my program 
>written in C, but at its core is a large case-when-end statement.  
>This is not `sexy.'  I was wondering if there was a better way to do 
>this in Ruby, or if I'm just missing the point.
>
>My code is at: http://manjac.ath.cx/nick/ruby-ibcm.rb
>

One thing I notice about your code that seems very C-ish is that you use 
only integers as options for your case statements.  Ruby's case 
statements are a lot more flexible than C's switch. (Maybe you need to do 
this because you're reading & executing a binary file of IBCM code.)  If 
you'd rather work at a higher level of abstraction with assembly code you 
could perhaps do  something like:


  case opcode
  when :halt
    #do halt stuff
  when :and
    #do and stuff
  when ...
  end



Or perhaps you could even define a set of opcode classes that each 
ecapsulate the bahavior of each opcode.  Then instead of a case statement 
you could just call a 'execute' (or whatever you want to call it) on each 
statement that you read, so it would look something like:

  class Machine
    include Singleton
    attr_accessor :accum
    def initialize
      @accum = 0 
      #define registers, states of the machine here
    end
  end

  class Add
    def initialize(value)
      @value=value
      @machine = Machine.instance
    end
    def execute
      @machine.accum += value  #scope of accum is an issue here, of course
    end
    def to_code #so you can convert the mnemonic to a code
      5         #this gives you an assembler for free, but I'm not sure
               
    end
  end

  def Add(value)
    Add.new(value)
  end

#...main loop

File.foreach("IBCM.program"){ |line|  #no more case statement
  op = eval(line.strip)
  op.execute #or if you want to convert to machine code: op.to_code
}


#contents of IBCM.program:

  Load(0x55)
  Add(2)
  And(0xFF)
  Xor(0x0F)
  #....


So then your IBCM.program files are actually valid Ruby code.
  

....but then again, if you've got to read in binary data anyway, 
maybe it wouldn't make sense to do it this way.

Phil