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:
“I am secretly afraid of animals.... I think it is because of the usness in their eyes, with the underlying not-usness which belies it, and is so tragic a reminder of the lost age when we human beings branched off and left them: left them to eternal inarticulateness and slavery. Why? their eyes seem to ask us.”
—Edith Wharton (1862–1937)
“And with the corner of a Creed,
The more shall be your meed.”
—John Skelton (1460?–1529)