I am writing a program which will tokenize the input text depending upon some specific rules. I am using C++ for this.
Rules
Letter 'a' should be converted to token 'V-A'
Letter 'p' should be converted to token 'C-PA'
Letter 'pp' should be converted to token 'C-PPA'
Letter 'u' should be converted to token 'V-U'
This is just a sample and in real time I have around 500+ rules like this. If I am providing input as 'appu', it should tokenize like 'V-A + C-PPA + V-U'. I have implemented an algorithm for doing this and wanted to make sure that I am doing the right thing.
Algorithm
All rules will be kept in a XML file with the corresponding mapping to the token. Something like
<rules>
<rule pattern="a" token="V-A" />
<rule pattern="p" token="C-PA" />
<rule pattern="pp" token="C-PPA" />
<rule pattern="u" token="V-U" />
</rules>
1 - When the application starts, read this xml file and keep the values in a 'std::map'. This will be available until the end of the application(singleton pattern implementation).
2 - Iterate the input text characters. For each character, look for a match. If found, become more greedy and look for more matches by taking the next characters from the input text. Do this until we are getting a no match. So for the input text 'appu', first look for a match for 'a'. If found, try to get more match by taking the next character from the input text. So it will try to match 'ap' and found no matches. So it just returns.
3 - Replace the letter 'a' from input text as we got a token for it.
4 - Repeat step 2 and 3 with the remaining characters in the input text.
Here is a more simple explanation of the steps
input-text = 'appu'
tokens-generated=''
// First iteration
character-to-match = 'a'
pattern-found = true
// since pattern found, going recursive and check for more matches
character-to-match = 'ap'
pattern-found = false
tokens-generated = 'V-A'
// since no match found for 'ap', taking the first success and replacing it from input text
input-text = 'ppu'
// second iteration
character-to-match = 'p'
pattern-found = true
// since pattern found, going recursive and check for more matches
character-to-match = 'pp'
pattern-found = true
// since pattern found, going recursive and check for more matches
character-to-match = 'ppu'
pattern-found = false
tokens-generated = 'V-A + C-PPA'
// since no match found for 'ppu', taking the first success and replacing it from input text
input-text = 'u'
// third iteration
character-to-match = 'u'
pattern-found = true
tokens-generated = 'V-A + C-PPA + V-U' // we'r done!
Questions
1 - Is this algorithm looks fine for this problem or is there a better way to address this problem?
2 - If this is the right method, std::map is a good choice here? Or do I need to create my own key/value container?
3 - Is there a library available which can tokenize string like the above?
Any help would be appreciated
:)