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:
“Summer set lip to earth’s bosom bare
And left the flushed print in a poppy there.”
—Francis Thompson (1859–1907)
“Have you not budged an inch, then? Such is the daily news. Its facts appear to float in the atmosphere.... We should wash ourselves clean of such news. Of what consequence, though our planet explode, if there is no character involved in the explosion? In health we have not the least curiosity about such events. We do not live for idle amusement. I would not run round a corner to see the world blow up.”
—Henry David Thoreau (1817–1862)