Solution
The correct answer is A → .
Key Points
- In the context of LR parsing in the field of computer science, an 'item' of a grammar rule represents a partially recognized rule. The dot in the item is used to indicate how much of a rule has been seen at a particular point in the parse process.
- For example, if we have a rule such as A -> BCD, when parsing begins, no part of the right side has been recognized, so the initial item is A -> .BCD. As parsing proceeds and B, C, and D are recognized, the dot moves rightward: A -> B.CD, A -> BC.D, and A -> BCD. respectively.
- Now, let's consider your rule A -> ε, which means that A can produce an empty string (epsilon). In the context of recognizing this rule, initially we've seen none of it, hence the item is A -> .. After recognizing the ε (meaning, recognizing that there's nothing to recognize), the item would be A -> ε..
- So, where we haven't parsed any symbols yet, the correct representation would be A -> .. The 'ε' isn't generally shown in the item because the dot alone indicates that no part of the right hand side has been seen, which is appropriate for a production that generates the empty string.
