I'm assuming you know what parsing is, and what syntax-directed translation is. If not, the wikipedia articles (http://en.wikipedia.org/wiki/Parsing and http://en.wikipedia.org/wiki/Syntax-directed_translation) offer a reasonable explanation.
The grammar file is generally laid out as follows:
Question ::= Phrase1 | Phrase2 | Phrase3 ...
Phrase1 ::= 'if' 'the' Noun 'is' Color 'what' 'color' 'is' 'it' [and now return the word which matched Color]
Noun ::= [sequence of characters]
Color ::= 'red' | 'blue' ...
The trickiest part of it was getting it to correctly interpret numbers like 'twenty one thousand eight hundred and ninety nine'
That part is basically laid out as
Number ::= Number QuantifiedNumber | Number 'and' QuantifiedNumber | QuantifiedNumber
QuantifiedNumber ::= NumberGroup | NumberGroup Quantifier
NumberGroup ::= SingleNumber SingleNumber | SingleNumber
SingleNumber ::= 'one' | 'two' | ... 'twenty' | 'thirty' | ...
I'm assuming you know what parsing is, and what syntax-directed translation is. If not, the wikipedia articles (http://en.wikipedia.org/wiki/Parsing and http://en.wikipedia.org/wiki/Syntax-directed_translation) offer a reasonable explanation.
The grammar file is generally laid out as follows:
Question ::= Phrase1 | Phrase2 | Phrase3 ...
Phrase1 ::= 'if' 'the' Noun 'is' Color 'what' 'color' 'is' 'it' [and now return the word which matched Color]
Noun ::= [sequence of characters]
Color ::= 'red' | 'blue' ...
The trickiest part of it was getting it to correctly interpret numbers like 'twenty one thousand eight hundred and ninety nine'
That part is basically laid out as
Number ::= Number QuantifiedNumber | Number 'and' QuantifiedNumber | QuantifiedNumber
QuantifiedNumber ::= NumberGroup | NumberGroup Quantifier
NumberGroup ::= SingleNumber SingleNumber | SingleNumber
SingleNumber ::= 'one' | 'two' | ... 'twenty' | 'thirty' | ...