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:
“Nothing will be left white but here a birch,
And there a clump of houses with a church.”
—Robert Frost (1874–1963)
“Knighterrantry is a most chuckleheaded trade, and it is tedious hard work, too, but I begin to see that there is money in it, after all, if you have luck. Not that I would ever engage in it, as a business, for I wouldn’t. No sound and legitimate business can be established on a basis of speculation. A successful whirl in the knighterrantry line—now what is it when you blow away the nonsense and come down to the cold facts? It’s just a corner in pork, that’s all.”
—Mark Twain [Samuel Langhorne Clemens] (1835–1910)