From: itsme213 <itsme213@...>
Date: 2005-04-12T13:09:39+09:00
Subject: Re: [ANN] cmd 0.7.0: Library for Line-Oriented Command Interpreters (initial release)


"Marcel Molina Jr." <marcel@vernix.org> wrote

> > Any plans to go towards interactive commands e.g. some commands valid
only
> > within scope of other commands?
>
> By interactive commands do you mean something like?
>
>   > foo
>   # now you are in a context within 'foo' that opens you up to a whole
other
>   # set of things

Sort-of ... lousy description on my part. I can see the command interpreter
as a state machine consisting of a current object + the available commands
on the current object. I'll start with the latter.

The available commands on the current object could change as you do things
to it. Suppose each of its commands has some declared pre-condition. A
command is disabled if its precondition is false. Here is one of many ways
to do this.

class PhoneBook < Cmd
  # ... define commands & docs
  pre :add { |pb| pb.condition_on_phonebook_add }
  pre :remove { |pb| pb.condition_on_phonebook_remove }
end

All commands whose pre is true are 'enabled', all others are 'greyed-out'.
Preconditions could have a descriptive string for help purposes.

Secondly the current object itself could be switched. e.g If you add some
special commands to "cd", "pushd", and "popd" to any command-able object, to
start working in a new command context.

PBook>    pushd `find Sam`
          - execute command "find Sam" in current context
          - perhaps check return (e.g. a Person) is command-able
          - make that the new command context, so ...
Sam>      first Sammy
          last Brown
          popd
PBook>

Plug in a Dir class and you have a command shell.

And, lastly, every command has arguments. Each argument has a range of valid
values that can depend on current state. If you store an array of blocks
that computes the possible values for each argument given the current
context object (when applicable), you can even provide completion for
arguments to commands.

class PhoneBook < Cmd
  # can only delete X if X currently in phonebook
  command :delete do
    args [  {|pb| pb.people.collect { |p| p.name }}
            # even better if returned objects, not strings
            # using to_s or some protocol to get strings for completion
            # command intereter keeps map of string->object
            # refuse to execute if no valid completion
            # inner code just deals with objects
         ]
  end
end

PBook> delete <TAB>
       #--> Sammy Mary
PBook> delete S<TAB>
       #--> delete Sammy


btw: have you considered adding a Command class to keep all info about one
command?