ahoward/main

NAME
  main.rb

SYNOPSIS
  a class factory and dsl for generating command line programs real quick

URI
  http://codeforpeople.com/lib/ruby/
  http://rubyforge.org/projects/codeforpeople/
  http://github.com/ahoward/main

INSTALL
  gem install main

DESCRIPTION
  main.rb features the following:

    - unification of option, argument, keyword, and environment parameter
      parsing
    - auto generation of usage and help messages
    - support for mode/sub-commands
    - io redirection support
    - logging hooks using ruby's built-in logging mechanism
    - intelligent error handling and exit codes 
    - use as dsl or library for building Main objects
    - parsing user defined ARGV and ENV
    - zero requirements for understanding the obtuse apis of *any* command
      line option parsers
    - leather pants

  in short main.rb aims to drastically lower the barrier to writing uniform
  command line applications.

  for instance, this program

    require 'main'

    Main {
      argument 'foo'
      option 'bar'

      def run
        p params['foo']
        p params['bar']
        exit_success!
      end
    }

  sets up a program which requires one argument, 'bar', and which may accept one
  command line switch, '--foo' in addition to the single option/mode which is always
  accepted and handled appropriately: 'help', '--help', '-h'.  for the most
  part main.rb stays out of your command line namespace but insists that your
  application has at least a help mode/option.

  main.rb supports sub-commands in a very simple way

    require 'main'

    Main {
      mode 'install' do
        def run() puts 'installing...' end
      end

      mode 'uninstall' do
        def run() puts 'uninstalling...' end
      end
    }

  which allows a program, called 'a.rb', to be invoked as

    ruby a.rb install

  and

    ruby a.rb uninstall

  for simple programs main.rb is a real time saver but it's for more complex
  applications where main.rb's unification of parameter parsing, class
  configuration dsl, and auto-generation of usage messages can really streamline
  command line application development.  for example the following 'a.rb'
  program:

    require 'main'

    Main {
      argument('foo'){
        cast :int
      }
      keyword('bar'){
        arity 2
        cast :float
        defaults 0.0, 1.0
      }
      option('foobar'){
        argument :optional
        description 'the foobar option is very handy'
      }
      environment('BARFOO'){
        cast :list_of_bool
        synopsis 'export barfoo=value'
      }

      def run
        p params['foo'].value
        p params['bar'].values
        p params['foobar'].value
        p params['BARFOO'].value
      end
    }

  when run with a command line of

    BARFOO=true,false,false ruby a.rb 42 bar=40 bar=2 --foobar=a

  will produce

    42
    [40.0, 2.0]
    "a"
    [true, false, false]

  while a command line of

    ruby a.rb --help

  will produce

    NAME
      a.rb

    SYNOPSIS
      a.rb foo [bar=bar] [options]+

    PARAMETERS
      * foo [ 1 -> int(foo) ]

      * bar=bar [ 2 ~> float(bar=0.0,1.0) ]

      * --foobar=[foobar] [ 1 ~> foobar ]
          the foobar option is very handy

      * --help, -h

      * export barfoo=value

  and this shows how all of argument, keyword, option, and environment parsing
  can be declartively dealt with in a unified fashion - the dsl for all
  parameter types is the same - and how auto synopsis and usage generation saves
  keystrokes.  the parameter synopsis is compact and can be read as

      * foo [ 1 -> int(foo) ]

        'one argument will get processed via int(argument_name)'

          1        : one argument
          ->       : will get processed (the argument is required)
          int(foo) : the cast is int, the arg name is foo

      * bar=bar [ 2 ~> float(bar=0.0,1.0) ]

        'two keyword arguments might be processed via float(bar=0.0,1.0)'

          2                  : two arguments
          ~>                 : might be processed (the argument is optional)
          float(bar=0.0,1.0) : the cast will be float, the default values are
                               0.0 and 1.0

      * --foobar=[foobar] [ 1 ~> foobar ]

        'one option with optional argument may be given directly'

      * --help, -h

        no synopsis, simple switch takes no args and is not required

      * export barfoo=value

        a user defined synopsis

SAMPLES

  <========< samples/a.rb >========>

  ~ > cat samples/a.rb

    require 'main'
    
    ARGV.replace %w( 42 ) if ARGV.empty?
    
    Main {
      argument('foo'){
        required                    # this is the default
        cast :int                   # value cast to Fixnum
        validate{|foo| foo == 42}   # raises error in failure case 
        description 'the foo param' # shown in --help
      }
    
      def run
        p params['foo'].given?
        p params['foo'].value
      end
    }

  ~ > ruby samples/a.rb

    true
    42


  <========< samples/b.rb >========>

  ~ > cat samples/b.rb

    require 'main'
    
    ARGV.replace %w( 40 1 1 ) if ARGV.empty?
    
    Main {
      argument('foo'){
        arity 3                             # foo will given three times
        cast :int                           # value cast to Fixnum
        validate{|foo| [40,1].include? foo} # raises error in failure case 
        description 'the foo param'         # shown in --help
      }
    
      def run
        p params['foo'].given?
        p params['foo'].values
      end
    }

  ~ > ruby samples/b.rb

    true
    [40, 1, 1]


  <========< samples/c.rb >========>

  ~ > cat samples/c.rb

    require 'main'
    
    ARGV.replace %w( foo=40 foo=2 bar=false ) if ARGV.empty?
    
    Main {
      keyword('foo'){
        required  # by default keywords are not required
        arity 2
        cast :float
      }
      keyword('bar'){
        cast :bool
      }
    
      def run
        p params['foo'].given?
        p params['foo'].values
        p params['bar'].given?
        p params['bar'].value
      end
    }

  ~ > ruby samples/c.rb

    true
    [40.0, 2.0]
    true
    false


  <========< samples/d.rb >========>

  ~ > cat samples/d.rb

    require 'main'
    
    ARGV.replace %w( --foo=40 -f2 ) if ARGV.empty?
    
    Main {
      option('foo', 'f'){
        required  # by default options are not required, we could use 'foo=foo'
                  # above as a shortcut
        argument_required
        arity 2
        cast :float
      }
    
      option('bar=[bar]', 'b'){  # note shortcut syntax for optional args
        # argument_optional      # we could also use this method
        cast :bool
        default false
      }
    
      def run
        p params['foo'].given?
        p params['foo'].values
        p params['bar'].given?
        p params['bar'].value
      end
    }

  ~ > ruby samples/d.rb

    true
    [40.0, 2.0]
    nil
    false


  <========< samples/e.rb >========>

  ~ > cat samples/e.rb

    require 'main'
    
    ARGV.replace %w( x y argument )
    
    Main {
      argument 'argument'
      option 'option'
    
      def run() puts 'run' end
    
      mode 'a' do
        option 'a-option'
        def run() puts 'a-run' end
      end
    
      mode 'x' do
        option 'x-option'
    
        def run() puts 'x-run' end
    
          mode 'y' do
            option 'y-option'
    
            def run() puts 'y-run' end
          end
      end
    }

  ~ > ruby samples/e.rb

    y-run


  <========< samples/f.rb >========>

  ~ > cat samples/f.rb

    require 'main'
    
    ARGV.replace %W( compress /data )
    
    Main {
      argument('directory'){ description 'the directory to operate on' }
    
      option('force'){ description 'use a bigger hammer' }
    
      def run
        puts 'this is how we run when no mode is specified'
      end
    
      mode 'compress' do
        option('bzip'){ description 'use bzip compression' }
    
        def run
          puts 'this is how we run in compress mode' 
        end
      end
    
      mode 'uncompress' do
        option('delete-after'){ description 'delete orginal file after uncompressing' }
    
        def run
          puts 'this is how we run in un-compress mode' 
        end
      end
    }

  ~ > ruby samples/f.rb

    this is how we run in compress mode


  <========< samples/g.rb >========>

  ~ > cat samples/g.rb

    require 'main'
    
    ARGV.replace %w( 42 ) if ARGV.empty?
    
    Main {
      argument( 'foo' )
      option( 'bar' )
    
      run { puts "This is what to_options produces: #{params.to_options.inspect}" }
    }

  ~ > ruby samples/g.rb

    This is what to_options produces: {"help"=>nil, "foo"=>"42", "bar"=>nil}


  <========< samples/h.rb >========>

  ~ > cat samples/h.rb

    require 'main'
    
    # block-defaults are instance_eval'd in the main instance and be combined with
    # mixins
    #
    # ./h.rb   #=> forty-two
    # ./h.rb a #=> 42 
    # ./h.rb b #=> 42.0 
    #
    
    Main {
      fattr :default_for_foobar => 'forty-two' 
    
      option(:foobar) do
        default{ default_for_foobar }
      end
    
      mixin :foo do
        fattr :default_for_foobar => 42
      end
    
      mixin :bar do
        fattr :default_for_foobar => 42.0
      end
    
    
      run{ p params[:foobar].value }
    
      mode :a do
        mixin :foo
      end
    
      mode :b do
        mixin :bar
      end
    }

  ~ > ruby samples/h.rb

    "forty-two"


  <========< samples/j.rb >========>

  ~ > cat samples/j.rb

    #!/usr/bin/env ruby
    
    require 'open-uri'
    
    require 'main'
    require 'digest/sha2'
    
    # you have access to a sequel/amalgalite/sqlite db for free
    #
    
    Main {
      name :i_can_haz_db
    
      db {
        create_table(:mp3s) do
          primary_key :id
          String :url
          String :sha
        end unless table_exists?(:mp3s)
      }
    
      def run
        url = 'http://s3.amazonaws.com/drawohara.com.mp3/ween-voodoo_lady.mp3'
        mp3 = open(url){|fd| fd.read}
        sha = Digest::SHA2.hexdigest(mp3)
    
        db[:mp3s].insert(:url => url, :sha => sha)
        p db[:mp3s].all
        p db
      end
    }

  ~ > ruby samples/j.rb

    [{:url=>"http://s3.amazonaws.com/drawohara.com.mp3/ween-voodoo_lady.mp3", :sha=>"54c99ac7588dcfce1e70540b734805e9c69ff98dcca001e6f2bdec140fb0f9dc", :id=>1}, {:url=>"http://s3.amazonaws.com/drawohara.com.mp3/ween-voodoo_lady.mp3", :sha=>"54c99ac7588dcfce1e70540b734805e9c69ff98dcca001e6f2bdec140fb0f9dc", :id=>2}]
    #<Sequel::Amalgalite::Database: "amalgalite://Users/ahoward/.i_can_haz_db/db.sqlite">



DOCS
  test/main.rb
  vim -p lib/main.rb lib/main/*rb
  API section below

HISTORY
  5.1.0
    - support for STATE_DIRNAME and STATE_BASENAME environment variables
  5.0.0
    ?
  4.4.0
    - support for automatic sequel/sqlite/amalgalite dbs for persistent state
      across invocations

        Main {
          db {
            create_table :foo do
              String key
              String val
            end unless table_exists? :foo
          }

          def run
            db[:foo].create(:key => 'using', :val => 'amalgalite')
          end
        }

      - support for automatic config files with auto populated template data

          Main {
            config :email => '[email protected]', :password => 'pa$$word'

            def run
              email = config[:email]
            end
          }

      - new paramter types :pathname, :path, :slug, :input, and :output 

      - input/output parameters.  can be filenames or '-' to supply
        stdin/stdout respectively

          Main {
            input :i
            output :o

            def run
              i = params[:i].value
              o = params[:o].value

              line = i.gets
              o.puts line
            end
          }

       - clean up warnings running with 'ruby -w'

       - fix a failing test

       - ability to ignore parameters in sub modes

          Main {
            argument :foo
            argument :bar

            def run
              p param[:bar].value
            end

            mode :ignoring do
              params[:foo].ignore!
            end
          }
  4.0.0
    - avoid duping ios.  new methods Main.push_ios! and Main.pop_ios! are
    utilized for testing.  this was done to make it simple to wrap
    daemon/servolux programs around main, althought not strictly required.
    not the version bump - there is not reason to expect existing main
    programs to break, but it *is* and interface change which requires a major
    version bump.

  3.0.0
    - major refactor to support modes via module/extend vs. subclassing.
    MIGHT NOT be backward compatible, though no known issues thus far.

  2.9.0
    - support ruby 1.9

  2.8.3
    - support for block defaults


  2.8.2
    - fixes and tests for negative arity/attr arguments, options, eg

        argument(:foo){
          arity -1  
        }

        def run  # ARGV == %w( a b c )
          p foo  #=> %w( a b c )
        end

      thanks nathan

  2.8.1
    - move from attributes.rb to fattr.rb

  2.8.0 
    - added 'to_options' method for Parameter::Table.  this allows you to convert
      all the parameters to a simple hash.  
      for example

        Main {
          option 'foo'
          argument 'baz'

          run { puts params.to_options.inspect } 

        }

  2.7.0
    - removed bundled arrayfields and attributes.  these are now dependancies
      mananged by rubygems.  a.k.a. you must have rubygems installed for main
      to work.

  2.6.0
    - added 'mixin' feaature for storing, and later evaluating a block of
      code.  the purpose of this is for use with modes where you want to keep
      your code dry, but may not want to define something in the base class
      for all to inherit.  'mixin' allows you to define the code to inherit
      once and the selectively drop it in child classes (modes) on demand.
      for example

        Main {
          mixin :foobar do
            option 'foo'
            option 'bar'
          end

          mode :install do
            mixin :foobar
          end

          mode :uninstall do
            mixin :foobar
          end

          mode :clean do
          end
        }

    - mode definitions are now deferred to the end of the Main block, so you
      can do this

        Main {
          mode 'a' do
            mixin :foo
          end

          mode 'b' do
            mixin :foo
          end

          def inherited_method
            42
          end

          mixin 'foo' do
            def another_inherited_method
              'forty-two'
            end
          end
        }

    - added sanity check at end of paramter contruction

    - improved auto usage generation when arity is used with arguments

    - removed 'p' shortcut in paramerter dsl because it collided with
      Kernel.p.  it's now called 'param'.  this method is availble *inside* a
      parameter definition

        option('foo', 'f'){
          synopsis "arity = #{ param.arity }"
        }
      
    - fixed bug where '--' did not signal the end of parameter parsing in a
      getoptlong compliant way

    - added (before/after)_parse_parameters, (before/after)_initialize, and
      (before/after)_run hooks

    - fixed bug where adding to usage via

        usage['my_section'] = 'custom message'

      totally horked the default auto generated usage message

    - updated dependancies in gemspec.rb for attributes (~> 5.0.0) and
      arrayfields (~> 4.3.0)

    - check that client code defined run, iff not wrap_run! is called.  this is
      so mains with a mode, but no run defined, still function correctly when 
      passed a mode

    - added new shortcut for creating accessors for parameters.  for example

        option('foo'){
          argument :required
          cast :int
          attr
        }

        def run
          p foo ### this attr will return the parameter's *value*
        end

      a block can be passed to specify how to extract the value from the
      parameter

        argument('foo'){
          optional
          default 21 
          cast :int
          attr{|param| param.value * 2}
        }

        def run
          p foo #=> 42 
        end

    - fixed bug where 'abort("message")' would print "message" twice on exit
      if running under a nested mode (yes again - the fix in 2.4.0 wasn't
      complete)

    - added a time cast, which uses Time.parse

        argument('login_time'){ cast :time }

    - added a date cast, which uses Date.parse

        argument('login_date'){ cast :date }
    

  2.5.0
    - added 'examples', 'samples', and 'api' kewords to main dsl.  each
      keyword takes a list of strings which will be included in the help
      message
        
        Main {
          examples "foobar example", "barfoo example"

          samples <<-txt
            do this

            don't do that
          txt

          api %(
            foobar string, hash

            barfoo hash, string
          ) 
        }

      results in a usage message with sections like

      ...

      EXAMPLES
        foobar example
        barfoo example

      SAMPLES
        do this

        don't do that

      API
        foobar string, hash

        barfoo hash, string

      ...

  2.4.0
    - fixed bug where 'abort("message")' would print "message" twice on exit
      if running under a nested mode.

    - allowed parameters to be overridden completely in subclasses (modes)

  2.3.0
    - re-worked Main.new such that client code may define an #initialize
      methods and the class will continue to work.  that is to say it's fine
      to do this

        Main {
          def initialize
            @a = 42
          end

          def run
            p @a
          end

          mode 'foo' do
            def run
              p @a
            end
          end
        }

      the client #initialize will be called *after* main has done it's normal
      initialization so things like @argv, @env, and @stdin will all be there
      in initialize.  of course you could have done this before but you'd have
      to both call super and call it with the correct arguments - now you can
      simply ignore it.

  2.2.0
    - added ability for parameter dsl error handlers to accept an argument,
      this will be passed the current error.  for example

        argument(:x) do
          arity 42
        
          error do |e|
            case e
              when Parameter::Arity
            ...
          end
        end  

    - refined the mode parsing a bit: modes can now be abbreviated to uniqness
      and, when the mode is ambiuous, a nice error message is printed, for
      example:

        ambiguous mode: in = (inflate or install)?

  2.1.0
    - added custom error handling dsl for parameters, this includes the ability
      to prepend, append, or replace the standard error handlers:

        require 'main'

        Main {
          argument 'x' do
            error :before do
              puts 'this fires *before* normal error handling using #instance_eval...'
            end

            error do
              puts 'this fires *instead of* normal error handling using #instance_eval...'
            end

            error :after do
              puts 'this fires *after* normal error handling using #instance_eval...'
            end
          end
          
          run(){ p param['x'].given? }
        }

    - added ability to exit at any time bypassing *all* error handling using
      'throw :exit, 42' where 42 is the desired exit status.  throw without a
      status simply exits with 0.

    - added 'help!' method which simply dumps out usage and exits

  2.0.0
    - removed need for proxy.rb via Main::Base.wrap_run!
    - added error handling hooks for parameter parsing
    - bundled arrayfields, attributes, and pervasives although gems are tried
      first
    - softened error messages for parameter parsing errors: certain classes of
      errors are now 'softspoken' and print only the message, not the entire
      stacktrace, to stderr.  much nicer for users.  this is configurable.
    - added subcommand/mode support
    - added support for user defined exception handling on top level
      exceptions/exits
    - added support for negative arity.  this users ruby's own arity
      semantics, for example:
      
        lambda{|*a|}.arity     == -1
        lambda{|a,*b|}.arity   == -2
        lambda{|a,b,*c|}.arity == -3
        ...

      in otherwords parameters now support 'zero or more', 'one or more' ...
      'n or more' argument semantics

  1.0.0
    - some improved usage messages from jeremy hinegardner

  0.0.2
    - removed dependancy on attributes/arrayfields.  main now has zero gem
      dependancies.

    - added support for io redirection.  redirection of stdin, stdout, and
      stderr can be done to any io like object or object that can be
      inerpreted as a pathname (object.to_s)

    - main objects can now easily be created and run on demand, which makes
      testing a breeze

        def test_unit_goodness!
          main = 
            Main.new{
              stdout StringIO.new 
              stderr '/dev/null'

              def run
                puts 42
              end
            }

          main.run
          main.stdout.rewind

          assert main.stdout.read == "42\n"
        end

    - added API section to readme and called it 'docs'

    - wrote a bunch more tests.  there are now 42 of them.

  0.0.1

    initial version.  this version extracts much of the functionality of alib's
    (gen install alib) Alib.script main program generator and also some of jim's
    freeze's excellent CommandLine::Aplication into what i hope is a simpler and
    more unified interface 

API

  Main {

  ###########################################################################
  #                       CLASS LEVEL API                                   #
  ###########################################################################
  #
  # the name of the program, auto-set and used in usage 
  #
    program 'foo.rb'
  #
  # a short description of program functionality, auto-set and used in usage
  #
    synopsis "foo.rb arg [options]+"
  #
  # long description of program functionality, used in usage iff set
  #
    description <<-hdoc
      this text will automatically be indented to the right level.

      it should describe how the program works in detail
    hdoc
  #
  # used in usage iff set
  #
    author '[email protected]'
  #
  # used in usage
  #
    version '0.0.42'
  #
  # stdin/out/err can be anthing which responds to read/write or a string
  # which will be opened as in the appropriate mode 
  #
    stdin '/dev/null'
    stdout '/dev/null'
    stderr open('/dev/null', 'w')
  #
  # the logger should be a Logger object, something 'write'-able, or a string
  # which will be used to open the logger.  the logger_level specifies the
  # initalize verbosity setting, the default is Logger::INFO
  #
    logger(( program + '.log' ))
    logger_level Logger::DEBUG
  #
  # you can configure exit codes.  the defaults are shown
  #
    exit_success # 0
    exit_failure # 1
    exit_warn    # 42
  #
  # the usage object is rather complex.  by default it's an object which can
  # be built up in sections using the 
  #
  #   usage["BUGS"] = "something about bugs'
  #
  # syntax to append sections onto the already pre-built usage message which
  # contains program, synopsis, parameter descriptions and the like
  #
  # however, you always replace the usage object wholesale with one of your
  # chosing like so
  #
    usage <<-txt
      my own usage message
    txt

  ###########################################################################
  #                         MODE API                                        #
  ###########################################################################
  #
  # modes are class factories that inherit from their parent class.  they can
  # be nested *arbitrarily* deep.  usage messages are tailored for each mode.
  # modes are, for the most part, independant classes but parameters are
  # always a superset of the parent class - a mode accepts all of it's parents
  # paramters *plus* and additional ones
  # 
    option 'inherited-option'
    argument 'inherited-argument'

    mode 'install' do
      option 'force' do
        description 'clobber existing installation'
      end

      def run
        inherited_method()
        puts 'installing...'
      end

      mode 'docs' do
        description 'installs the docs'

        def run
          puts 'installing docs...'
        end
      end
    end

    mode 'un-install' do
      option 'force' do
        description 'remove even if dependancies exist'
      end

      def run
        inherited_method()
        puts 'un-installing...'
      end
    end

    def run
      puts 'no mode yo?'
    end

    def inherited_method
      puts 'superclass_method...'
    end


  ###########################################################################
  #                         PARAMETER API                                   #
  ###########################################################################
  #
  # all the parameter types of argument|keyword|option|environment share this
  # api.  you must specify the type when the parameter method is used.
  # alternatively used one of the shortcut methods
  # argument|keyword|option|environment.  in otherwords
  #
  #   parameter('foo'){ type :option } 
  #
  # is synonymous with
  #
  #   option('foo'){ } 
  #
    option 'foo' {
    #
    # required - whether this paramter must by supplied on the command line.
    # note that you can create 'required' options with this keyword
    #
      required # or required true
    #
    # argument_required - applies only to options.
    #
      argument_required # argument :required
    #
    # argument_optional - applies only to options.
    #
      argument_optional # argument :optional
    #
    # cast - should be either a lambda taking one argument, or a symbol
    # designation one of the built in casts defined in Main::Cast.  supported
    # types are :boolean|:integer|:float|:numeric|:string|:uri.  built-in
    # casts can be abbreviated
    #
      cast :int
    #
    # validate - should be a lambda taking one argument and returning
    # true|false
    #
      validate{|int| int == 42}
    #
    # synopsis - should be a concise characterization of the paramter.  a
    # default synopsis is built automatically from the parameter.  this
    # information is displayed in the usage message
    #
      synopsis '--foo'
    #
    # description - a longer description of the paramter.  it appears in the
    # usage also.
    #
      description 'a long description of foo'
    #
    # arity - indicates how many times the parameter should appear on the
    # command line.  the default is one.  negative arities are supported and
    # follow the same rules as ruby methods/procs.
    #
      arity 2
    #
    # default - you can provide a default value in case none is given.  the
    # alias 'defaults' reads a bit nicer when you are giving a list of
    # defaults for paramters of > 1 arity
    #
      defaults 40, 2
    #
    # you can add custom per-parameter error handlers using the following
    #
      error :before do
        puts 'this fires *before* normal error handling using #instance_eval...'
      end

      error do
        puts 'this fires *instead of* normal error handling using #instance_eval...'
      end

      error :after do
        puts 'this fires *after* normal error handling using #instance_eval...'
      end
    }

  ###########################################################################
  #                       INSTANCE LEVEL API                                #
  ###########################################################################
  #
  # you must define a run method.  it is the only method you must define.
  #
    def run
      #
      # all parameters are available in the 'params' hash and via the alias
      # 'param'.  it can be indexed via string or symbol.  the values are all
      # Main::Parameter objects
      #
        foo = params['foo']
      #
      # the given? method indicates whether or not the parameter was given on
      # the commandline/environment, etc.  in particular this will not be true
      # when a default value was specified but no parameter was given 
      #
        foo.given?
      #
      # the list of all values can be retrieved via 'values'.  note that this
      # is always an array.
      #
        p foo.values
      #
      # the __first__ value can be retrieved via 'value'.  note that this
      # never an array.
      #
        p foo.value
      #
      # the methods debug|info|warn|error|fatal are delegated to the logger
      # object
      #
        info{ "this goes to the log" }
      #
      # you can set the exit_status at anytime.  this status is used when
      # exiting the program.  exceptions cause this to be ext_failure if, and
      # only if, the current value was exit_success.  in otherwords an
      # un-caught exception always results in a failing exit_status
      #
        exit_status exit_failure
      #
      # a few shortcuts both set the exit_status and exit the program.
      #
        exit_success!
        exit_failure!
        exit_warn!
    end

  }