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:
“On the 31st of August, 1846, I left Concord in Massachusetts for Bangor and the backwoods of Maine,... I proposed to make excursions to Mount Ktaadn, the second highest mountain in New England, about thirty miles distant, and to some of the lakes of the Penobscot, either alone or with such company as I might pick up there.”
—Henry David Thoreau (1817–1862)
“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)