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:
“It is extraordinary how the house and the simplest possessions of someone who has been left become so quickly sordid.... Even the stain on the coffee cup seems not coffee but the physical manifestation of one’s inner stain, the fatal blot that from the beginning had marked one for ultimate aloneness.”
—Coleman Dowell (1925–1985)
“And with the corner of a Creed,
The more shall be your meed.”
—John Skelton (1460?–1529)