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:
“He was a lucky fox that left his tail in the trap. The muskrat will gnaw his third leg off to be free. No wonder man has lost his elasticity.”
—Henry David Thoreau (1817–1862)
“People think that if a man has undergone any hardship, he should have a reward; but for my part, if I have done the hardest possible day’s work, and then come to sit down in a corner and eat my supper comfortably—why, then I don’t think I deserve any reward for my hard day’s work—for am I not now at peace? Is not my supper good?”
—Herman Melville (1819–1891)