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 tell you there isn’t a thing under the sun that needs to be done at all, but what a man can do better than a woman, unless it’s bearing children, and they do that in a poor make-shift way; it had better ha’ been left to the men.”
—George Eliot [Mary Ann (or Marian)
“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)