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:
“Most magazines have that look of being predestined to be left which one sees on the faces of the women whose troubles bring them to the Law Courts.”
—Rebecca West (1892–1983)
“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)