From: "Gulyás Attila" <toraritte@...>
Date: 2013-02-12T19:50:23+09:00
Subject: Re: Playing with DSLs, a question or two

Hi,

Dwemthy's Array by Why can also be helpful
http://mislav.uniqpath.com/poignant-guide/dwemthy/

ati

On 2/11/13, Peter Hickman <peterhickman386@googlemail.com> wrote:
> Thanks Ryan.
>
> That was just the sort of thing I was looking for.
>
> Thanks for that.
>
>
> On 11 February 2013 17:18, Ryan Cook <cookrn@gmail.com> wrote:
>
>> Hey Peter,
>>
>> How does this look? https://gist.github.com/cookrn/4755773
>>
>> By making the Room a separate object, the scoping might be more as you
>> had
>> hoped e.g. the door method
>>
>> Regarding the yield vs. instance_eval -- this is a matter of opinion. If
>> you wanted to be very explicit, you could yield the adventure and room
>> objects to the blocks given to those methods. This makes your DSL seem a
>> bit less magic, but maybe that's ok.
>>
>> I gave a talk on DSLs at Boulder Ruby a while back that you might find
>> interesting: https://speakerdeck.com/cookrn/dsls-as-teaching-tools
>>
>> Ryan
>>
>>
>> On Mon, Feb 11, 2013 at 8:18 AM, Peter Hickman <
>> peterhickman386@googlemail.com> wrote:
>>
>>> I am playing around with writing some DSLs to help me get more familier
>>> with how they work and I have a couple of questions. First here's an
>>> example of one I am playing with (based on the classic dungeon adventure
>>> problem)
>>>
>>> class Adventure
>>>   def initialize
>>>     @rooms = Hash.new
>>>     @current_room = nil
>>>   end
>>>
>>>   def room(reference, &block)
>>>     if @rooms.has_key?(reference)
>>>       puts "Error: Room #{reference} has already been defined"
>>>     else
>>>       @rooms[reference] = {:short => '', :long => '', :exits =>
>>> Hash.new}
>>>     end
>>>
>>>     @current_room = reference
>>>
>>>     yield block
>>>   end
>>>
>>>   def short(text)
>>>     @rooms[@current_room][:short] = text
>>>   end
>>>
>>>   def long(text)
>>>     @rooms[@current_room][:long] = text
>>>   end
>>>
>>>   def door(direction, destination, &block)
>>>     if @rooms[@current_room][:exits].has_key?(direction)
>>>       puts "Error: Room #{@current_room} already has an exit defined in
>>> #{direction}"
>>>     else
>>>       @rooms[@current_room][:exits][direction] = {:where => destination,
>>> :condition => block_given? ? block : true}
>>>     end
>>>   end
>>> end
>>>
>>> class Object
>>>   def adventure(&block)
>>>     a = Adventure.new
>>>
>>>     a.instance_eval(&block)
>>>   end
>>> end
>>>
>>> adventure do
>>>   room :cave do
>>>     short "You are in a large cave"
>>>     long "You are in a very large cave"
>>>     door :west, :another_cave
>>>     door :east, :exit do
>>>       if player.has_item(:key)
>>>         true
>>>       else
>>>         false
>>>       end
>>>     end
>>>   end
>>>
>>>   room :another_cave do
>>>     short "A cave"
>>>     long "Oh great ... another cave"
>>>     door :east, :cave
>>>   end
>>>
>>>   room :exit do
>>>     short "Freedom"
>>>     long "Freeeeeeeeeeedom!!!!!!"
>>>     door :west, :cave
>>>   end
>>>
>>>   require 'pp'
>>>   pp @rooms
>>> end
>>>
>>> Now this works just fine but a couple of things just don't seem right.
>>> Notice the @current_room variable that is set in the room method and
>>> referenced in short, long and door. This seems clunky - it is basically
>>> a
>>> global variable to help tie things together. Is there some better way of
>>> doing this? Perhaps by passing it as a parameter somehow.
>>>
>>> Also is the yield at the bottom of the room method the right way to go
>>> or
>>> should I be calling instance_eval or similar?
>>>
>>> Also how do I stop, for example, the door method being called outside of
>>> the room method? I have a solution where I set @current_room to nil
>>> after
>>> the yield and then each method checks to see if it is set and if not it
>>> errors. But again this seems to be quite a pain.
>>>
>>>
>>
>>
>> --
>> Ryan Cook
>> 720.319.7660
>>
>