gistfile1.txt

class Parser
rule
	target		:	unit
			|			{ result = 0 }

	unit		:	stat
			|	unit stat
	stat		:	expr SEMICOLON

	expr_list	:	expr
			|	expr_list expr

	expr		:	bind
			|	lambda
			|	applicative

	term		:	IDENTIFIER			{ result = Reference.new(val[0]) }
			|	INTEGER				{ result = Constant.new(val[0]) }
			|	STRING				{ result = Constant.new(val[0]) }
			|	LETTER				{ result = Constant.new(val[0]) }
			|	LPAREN RPAREN			{ result = Constant.new([]) }
			|	LPAREN expr_list RPAREN		{ result = val[1] }


	bind		:	LET IDENTIFIER COLON expr
			|	LET IDENTIFIER COLON expr ARROW expr

	lambda		:	LAMBDA IDENTIFIER ARROW expr

	applicative	:	term
			|	applicative term		{ result = Applicative.new(val[0],val[1]) }
end

----header

class Contant
   def initialize(value)
      @value = value
   end

   def evaluate(scope)
      @value
   end

   def to_s()
     "\"#{@value}\""
   end
end

class Reference
   def initialize(id)
      @id = id
   end

   def evaluate(scope)
      scope[@id]
   end

   def to_s()
      "#{@id}"
   end
end

class Cell
   def initialize(car,cdr)
      @car = car
      @cdr = cdr
   end

   def evaluate(scope)
      [@car,@cdr]
   end

   def to_s()
      "(#{@car},#{@cdr})"
   end
end

class Lambda
   def initialize(id,expr)
      @id = id
      @expr = expr
   end

   def evaluate(scope)
      lambda { |arg|
         scope[@id] = arg
         @expr.evaluate(@id)
      }
   end

   def to_s()
      "(#{@id} -> #{@expr})"
   end
end

class Applicative
   def initialize(expr,parameter)
      @expr = expr
      @parameter = parameter
   end

   def evaluate(scope)
      
   end

   def to_s()
      "(#{@expr} #{@parameter})"
   end
end

class Scope
   def initialize(parent= nil,table = init_table())
      @parent = parent
      @table = table
   end

   def []=(id,value)
      @table[id] = value
   end

   def [](id)
      result = self[id]
      return result if result
      if self.parent
        self.parent[id]
      else
        nil
      end
   end

   def local()
      Scope.new(self,{})
   end

   def parent()
      @parent
   end

   def init_table()
     table = {}

     table
   end
end