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:
“It’s so lonely here. Like we were the only two people left in the whole world. Maybe we are. Maybe when we get back to shore everybody else will have disappeared. I’d like that, wouldn’t you?”
—Michael Wilson (1914–1978)
“There’s only one corner of the universe you can be certain of improving, and that’s your own self.”
—Aldous Huxley (1894–1963)