From: Alec Ross <alec@...>
Date: 2006-02-02T19:23:17+09:00
Subject: Re: Grammars (mini-scripting languages)

In message <2548bfcd61b269091ed82e31994ade42@ruby-forum.com>, Michael 
Judge <mjudge@surveycomplete.com> writes
>Ross Bamford wrote:
>> On Thu, 2006-02-02 at 09:57 +0900, Michael Judge wrote:
>>
>>>     1. Storing executable code in the database is a security problem
>>>     2. instance_eval is slow
>>>     3. The alternative (a big if/elsif tree) would span many pages and
>>> be unweildy.
>>>
>>> Have a better suggestion?
>>
>> Not necessarily better, but how about something like:
>>
>>      class Commands
>>         [snip]
>>        def dispatch(line)
>>          if line =~ /([QXM])-?(.*)/
>>            send($1.intern, $2)
>>          else
>>            raise "Invalid input: #{line}"
>>          end
>>        end
>>      end
>
>That's neat, Ross.  I wasn't familiar with the send command.  Looks like
>the consequence is that the grammar has to fit an easy regular
>expression or you'd be duplicating it in the match and again in the
>method definition... Well, that's not necessarily a bad thing.
>Consistency is good too.
>
>I need to think about this.
>
>What do programmers normally do when they have a case statement that's
>30 or more items long?  Previously I've just left it as a case statement
>and spent the life of the project ticked at it.
>

My inclination is generally to drive the execution by table lookup.

-- 
Alec Ross