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:
“My only companions were the mice, which came to pick up the crumbs that had been left in those scraps of paper; still, as everywhere, pensioners on man, and not unwisely improving this elevated tract for their habitation. They nibbled what was for them; I nibbled what was for me.”
—Henry David Thoreau (1817–1862)
“All that Shakespeare says of the king, yonder slip of a boy that reads in the corner feels to be true of himself.”
—Ralph Waldo Emerson (1803–1882)