Updating Tomáš Matoušek’s repl.rb & adding repl.py

In April 2009, Tomáš Matoušek created a nifty IronRuby script that demonstrated the sharing of ScriptScopes in the Dynamic Language Runtime (DLR). The examples on Tomáš’ blog post still work.

The script is like the movie Inception, with languages within languages; but at its core shows how the DLR permits object sharing between languages within the same scope. The code itself is IronRuby; the script spins up a new ScriptRuntime and Engine to perform the acrobatics.

NOTE: These two small scripts are now published to my github account

As IronRuby has moved to 1.1.x.x, and supporting the Ruby 1.9.x language, I’ve updated the code a little (essentially, replacing ‘:’ with ‘then’)

Code Snippet

1. load_assembly 'Microsoft.Scripting'
2. Hosting = Microsoft::Scripting::Hosting
3. Scripting = Microsoft::Scripting
4.  
5. class REPL
6.   def initialize
7.     @engine = IronRuby.create_engine
8.     @scope = @engine.create_scope
9.     @exception_service = @engine.method(:get_service).of(Hosting::ExceptionOperations).call
10.     @language = "rb"
11.   end
12.  
13.   def run
14.     while true
15.       print "#@language> "
16.       line = gets
17.       break if line.nil?
18.  
19.       if line[0] == ?#
20.         execute_command line[1..-1].rstrip
21.       else
22.         execute_code read_code(line)
23.       end
24.     end
25.   end
26.  
27.    # Reads lines from standard input until a complete or invalid code snippet is entered.
28.   # Returns ScriptSource that represents an interactive code.
29.   def read_code first_line
30.     code = first_line
31.     while true
32.       interactive_code = @engine.create_script_source_from_string(code, Scripting::SourceCodeKind.InteractiveCode)
33.       case interactive_code.get_code_properties
34.         when Scripting::ScriptCodeParseResult.Complete, Scripting::ScriptCodeParseResult.Invalid then
35.           return interactive_code
36.  
37.         else
38.           print "#@language| "
39.           next_line = gets
40.           return interactive_code if next_line.nil? or next_line.strip.size == 0
41.           code += next_line
42.       end
43.     end
44.   end
45.  
46.   # Executes given ScriptSource and prints any exceptions that it might raise.
47.   def execute_code source
48.     source.execute(@scope)
49.   rescue Exception => e
50.     message, name = @exception_service.get_exception_message(e)
51.     puts "#{name}: #{message}"
52.   end
53.  
54.   def execute_command command
55.     case command
56.       when 'exit' then exit
57.       when 'ls?' then display_languages
58.       else puts "Unknown command '#{command}'" unless switch_language command
59.     end
60.   end
61.  
62.   def display_languages
63.     @engine.runtime.setup.language_setups.each { |ls| puts "#{ls.display_name}: #{ls.names.inspect}" }
64.   end
65.  
66.   def switch_language name
67.     has_engine, engine = @engine.runtime.try_get_engine(name)
68.     @language, @engine = name, engine if has_engine
69.     has_engine
70.   end
71. end
72.  
73. REPL.new.run

In my Pycon-AU keynote, I demonstrated the above piece of fun. Showing Ruby in a Python keynote did not result in my immediate death – just in case, for the forthcoming Kiwi Pycon I decided to rewrite this in IronPython:

Code Snippet

1. import clr, sys
2. clr.AddReference("Microsoft.Scripting")
3. from Microsoft.Scripting import *
4.  
5. class REPL :
6.     def __init__ (self) :
7.         self.currentlanguage = "py"
8.         self.runtime = Hosting.ScriptRuntime.CreateFromConfiguration()
9.         self.engine = self.runtime.GetEngineByFileExtension(self.currentlanguage)
10.         self.scope = self.engine.CreateScope()
11.     def run (self) :
12.         while (True) :
13.             scriptinput = raw_input("{0}> ".format(self.currentlanguage))
14.             if scriptinput == "" :
15.                 sys.exit()
16.             if scriptinput[0] == "#" :
17.                 self.execute_command(scriptinput[1:])
18.             else :
19.                 self.execute_code(self.read_code(scriptinput))
20.     def read_code(self, firstline):
21.         code = firstline
22.         while (True) :
23.             interactivecode = self.engine.CreateScriptSourceFromString(code, SourceCodeKind.InteractiveCode)
24.             parseresult = interactivecode.GetCodeProperties()
25.             if parseresult ==  ScriptCodeParseResult.Complete or parseresult == ScriptCodeParseResult.Invalid :
26.                 return interactivecode
27.             else :
28.                 scriptinput = raw_input("{0}| ".format(self.currentlanguage))
29.                 if scriptinput == "" :
30.                     return interactivecode
31.                 else :
32.                     code = code + "\n" + scriptinput
33.     def execute_code(self, source):
34.         try:
35.             source.Execute(self.scope)
36.         except Exception, e:
37.             print "{0}".format(e)
38.     def execute_command(self, command):
39.         if command == 'exit' :
40.             sys.exit()
41.         elif command == 'ls' :
42.             self.display_languages()
43.         else :
44.             self.engine = self.switch_language(command)
45.     def display_languages (self) :
46.         for i in self.engine.Runtime.Setup.LanguageSetups:
47.             print '{0}'.format(i.DisplayName)
48.     def switch_language(self, name) :
49.         old_engine = self.engine
50.         try :
51.             new_engine = self.runtime.GetEngineByFileExtension(name)
52.             self.currentlanguage = name
53.         except :
54.             print "{0} is an unknown script engine file association".format(name)
55.             new_engine = old_engine
56.         return new_engine
57.  
58. r = REPL()
59. r.run()