From: Robert Klemme <lists@...>
Date: 2012-04-04T17:05:57+09:00
Subject: Re: RegEx for a string between two symbols

Jan E. wrote in post #1054940:
> Christopher D. wrote in post #1054934:
>> Hey, thanks for the reply. I've been practising my ruby but if you have
>> a JSON or XML solution I will look at / learn those too as Ruby is often
>> used in tandem with XML and JSON
>>
>> So I'm looking to start up a text file where I can type words and then
>> its corresponding definition on the same line. For example.
>>
>> In dictionary.txt I would have
>> word1 - definition1;
>> word2 - definition2;
>
> If it's only one word and one definition per line, then XML or JSON is
> probably too much. But I wouldn't use a hyphen as a separator, because
> it may also appear in words or definitions. Use something special like a
> double colon:
>
> word :: definition
>
> You don't have to mark the end of the definition, because you can simply
> read the whole line.
>
> The "parser" could be something like this:
>
> ####
> dictionary = {}
> File.foreach 'C:/dictionary.txt' do |line|
>   next if line.strip.empty?             # skip empty lines
>   parts = line.split('::').map &:strip  # split line at the double colon

That's unsafe because it will break if there is a '::' in the 
definition.

>   if parts.length == 2 and parts.none? &:empty?
>     word, definition = parts
>     raise "multiple definitions for #{word}" if
>         dictionary.has_key? word.to_sym
>     dictionary[word.to_sym] = definition
>   else
>     raise "invalid line: #{line}"
>   end
> end
>
> p dictionary
> ####

I would separate parsing and dictionary building.  For example

def read_dict(file_name)
  File.foreach file_name do |line|
    line.chomp!

    if %r{\A\s*(\w+)\s*::\s*+(.*?)\s*\z} =~ line
      yield $1, $2 # word, def
    else
      raise "invalid line: #{line}"
    end
  end
end

def load_dict(file_name)
  dict = {}

  read_dict file_name do |word, definition|
    raise "multiple definitions for #{word}" if
      dict.has_key? word

    dict[word] = definition
  end

  dict
end

Btw, I wouldn't use symbols for the words because there are potentially 
many and they are not GC'ed.

Kind regards

robert

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