The left corner of a production rule in a context-free grammar is the left-most symbol on the right side of the rule.
For example, in the rule A→Xα, X is the left corner.
The left corner table associates a symbol with all possible left corners for that symbol, and the left corners of those symbols, etc.
Given the grammar
- S→VP
- S→NP VP
- VP→V NP
- NP→DET N
| Symbol | Left corner(s) |
|---|---|
| S | VP, NP, V, DET |
| NP | Det |
| VP | V |
Left corners are used to add bottom-up filtering of a top-down parser.
You can use the left corners to do top-down filtering of a bottom-up parser.
Famous quotes containing the words left and/or corner:
“Where has it gone, the lifetime?
Search me. What’s left is drear.
Unchilded and unwifed, I’m
Able to view that clear:
So final. And so near.”
—Philip Larkin (1922–1986)
“... research is never completed ... Around the corner lurks another possibility of interview, another book to read, a courthouse to explore, a document to verify.”
—Catherine Drinker Bowen (1897–1973)