Overview of the parse () Function

The parse() function declares the bit stream pattern as an array of twenty characters, then it initialises the array to null. It creates an array to hold the output of up to two hundred and fifty characters. Parse() begins by breaking down the incoming sentence into numerical values to give the bit stream pattern. The function uses two counters to compare each string in the sentence to the words in each lexical array in order to identify them as either a verb, adjective, interrogative etc. On discovering a match, the bit stream pattern is assigned the numerical value of the lexical array i.e. verb is 4, interrogative is 6. For example, the bit stream pattern that would be assigned to "What does he like?" is 6434, interrogative, verb, pronoun and verb.

At the end of the parse() function there is a list of patterns that the program considers to be correct. At the moment, the list consists of two patterns. The patterns considered to be legal to the program are extensible. If the pattern is considered to be legal, it is passed to response(). If this is not the case, an error messages is selected at random and passed to display(). For example, " I beg your pardon" or "I don�t understand the question".

Overview of the response () Function

Response() takes as its argument, a pointer to pattern. That is, the address of pattern is passed to the function. The function creates an array for the response of up to two hundred and fifty six characters, and initialises it to null or empty. In this function a flag �ok� is created as an integer value. The flag is used as a switch. If it is set to 0, a line of code is read. If it is set to 1, the same line of code is not read. This was for simplicity. It is worth mentioning only because it is the only use of a flag in the program.

At points in response(), the statement "If the pattern of the question is a match for this pattern then do this" appears. If the answer is true, the following code will be executed. If not, the program will jump to the next occurrence of the same statement, holding a different pattern. The code that handles each pattern will generate a response using a different grammatical structure.

For the example "what does he like?" the match is pattern 643. The number �6� represents an interrogative. The list of interrogatives is now given a question identity. �What� now has an ident_question identity of �What�. The question identity will be used to match the response to a suitable collection of templates, from the template file.

The rewrite rules then look at the input pronoun and select an appropriate response for whichever one is used. The verb is then examined in order to make a grammatically correct response. If the sentence is longer than three words (which is the length of the pattern in this case), the next word is examined. If the next word is a verb listed in the lexicon, then it is included in the response. If the first verb is �does�, then the second verb may have to have �s� or �es� added to it. The rewrite rules perform this. In our example, the response generated should be "he likes�.". However, "What do you like" should return "I like�.". If the fourth word in the input sentence is a prepositional, the remainder of the sentence is taken into the response. For example, " Why is he here today in this rain?" should return "he is here today in this rain�". The examples show that it is possible to write code that deals with the pattern of the input sentence and to generate a response that is grammatically correct. If transitive and intransitive verbs had been listed as separate classes, this would be more apparent. If a transitive verb is found in the sentence, the rest of the sentence could be included in the response, as it is with the prepositional.

Once a response has been generated, it is inserted into a template from the template file. This is one of the reasons for having question identities. The last two commands in response() are to pass the sentence and the question identity to templ_database() and display(outp) which sends to display() the output, returned from templ_database.