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:
“The path was a vague parting in the grass
That led us to a weathered windowsill.
We pressed our faces to the pane. “You see,” he said,
“Everything’s as she left it when she died....””
—Robert Frost (1874–1963)
“Many said selfishness was the flaw of our modern age; but then self-conceit emerged from a corner of the deepest hell to join selfishness.”
—Franz Grillparzer (1791–1872)