Initial import of Russ's first version

README.md

@@ -0,0 +1,13 @@
+russ forth
+==========
+
+A simple Forth interpreter in Ruby (1.9).
+
+    1 2 dup + +
+    .
+    5
+    
+    3 2 1 + *
+    .
+    9
+

src/rforth.rb

@@ -0,0 +1,128 @@
+require 'pp'
+
+class Dictionary
+  def initialize
+    @entries = {}
+  end
+
+  def word( name, &block )
+    @entries[name] = { :name => name, :block => block, :immediate => false }
+  end
+
+  def immediate_word( name, &block )
+    @entries[name] = { :name => name, :block => block, :immediate => true }
+  end
+
+  def []( name )
+    @entries[name]
+  end
+end
+
+class RForth
+
+  def initialize( s_in = $stdin, s_out = $stdout )
+    @s_in = s_in
+    @s_out = s_out
+    @dictionary = initial_dictionary
+    @stack = []
+  end
+
+  def initial_dictionary
+    d = Dictionary.new
+    d.word(':') { define_word }
+    d.word('.'){ @s_out.print( @stack.pop ) }
+    d.word('cr') { @s_out.puts }
+    d.word('+') { @stack << (@stack.pop + @stack.pop) }
+    d.word('*') { @stack << (@stack.pop * @stack.pop) }
+    d.word('-') do
+      a = @stack.pop
+      b = @stack.pop
+      @stack << b - a
+    end
+
+    d.word('/') do
+      a = @stack.pop
+      b = @stack.pop
+      @stack << b / a
+    end
+    d
+  end
+
+  def define_word
+    name = read_word
+    blocks = []
+    while (word = read_word)
+      break if word == ';'
+      entry = @dictionary.word(word)
+      raise "no such word: #{word}" unless entry
+      if entry[:immediate]
+        entry[:block].call
+      else
+        blocks << entry[:block]
+      end
+    end
+
+    @dictionary.word(name) do
+      blocks.each {|b| b.call}
+    end
+  end
+
+  def forth_eval( word )
+    if @dictionary[word]
+      @dictionary[word][:block].call
+    elsif (x = to_number(word))
+      @stack << x
+    else
+      @s_out.puts "#{word} ??"
+    end
+  end
+
+  def to_number( word )
+    begin
+      return Integer( word )
+    rescue
+      puts $!
+    end
+    begin
+      return Float( word )
+    rescue
+      puts $!
+    end
+    nil
+  end
+
+  def read_char
+    @s_in.readchar
+  end
+
+  def read_word
+    result = nil
+    ch = nil
+    until @s_in.eof?
+      ch = read_char
+      if result and is_space?(ch)
+        break
+      elsif result.nil?
+        result = ch
+      else
+        result << ch
+      end
+    end
+    return result if result
+    nil
+  end
+
+  def is_space?( ch )
+    /\W/ =~ ch
+  end
+
+  def run
+    until $stdin.eof?
+      @s_out.flush
+      word = read_word
+      forth_eval( word )
+    end
+  end
+end
+
+RForth.new.run