module DynamicVars

# File lib/dynamic_vars.rb, line 37
def [](key)
  variables[key]
end

# File lib/dynamic_vars.rb, line 41
def []=(key, value)
  variables[key] = value
end

# File lib/dynamic_vars.rb, line 7
def here!
  Thread.current[:DYNAMIC] = Hash.new { |hash, key|
    raise NameError, "no such dynamic variable: #{key}"
  }.update Thread.main[:DYNAMIC]
end

# File lib/dynamic_vars.rb, line 52
def let(bindings, &block)
  save = {}
  bindings.to_hash.collect { |key, value|
    save[key] = self[key]
    self[key] = value
  }
  begin
    block.call
  ensure
    variables.update save
  end
end

# File lib/dynamic_vars.rb, line 65
def method_missing(name, *args)
  if match = /=\Z/.match(name.to_s)    # setter?
    raise ArgumentError, "invalid setter call"  unless args.size == 1
    self[match.pre_match.intern] = args.first
  else
    raise ArgumentError, "invalid getter call"  unless args.empty?
    self[name]
  end
end

# File lib/dynamic_vars.rb, line 45
def undefine(*keys)
  keys.each { |key|
    self[key]
    variables.delete key
  }
end

# File lib/dynamic_vars.rb, line 17
def variable(definition)
  case definition
  when Symbol
    if variables.has_key? definition
      raise NameError, "dynamic variable `#{definition}' already exists"
    end
    variables[definition] = nil
  when Hash
    definition.each { |key, value|
      if variables.has_key? key
        raise NameError, "dynamic variable `#{key}' already exists"
      end
      variables[key] = value
    }
  else
    raise ArgumentError,
    "can't create a new dynamic variable from #{definition.class}"
  end
end

# File lib/dynamic_vars.rb, line 13
def variables
  Thread.current[:DYNAMIC] or here!
end