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:
“I realized that, while I would never be my mother nor have her life, the lesson she had left me was that it was possible to love and care for a man and still have at your core a strength so great that you never even needed to put it on display.”
—Anna Quindlen (b. 1952)
“If I should die, think only this of me:
That there’s some corner of a foreign field
That is for ever England.”
—Rupert Brooke (1887–1915)