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:
“Zola: I need someone to remind me of the old, struggling, carefree days. Fighting for a foothold.
Paul Cézanne: You can never go back to it. And I never left it.”
—Norman Reilly Raine (1895–1971)
“Good Lord, for alliance! Thus goes every one to the world but I, and I am sunburnt; I may sit in a corner and cry “Heigh-ho for a husband!””
—William Shakespeare (1564–1616)