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:
“The path was a vague parting in the grass
That led us to a weathered windowsill.
We pressed our faces to the pane. “You see,” he said,
“Everything’s as she left it when she died....””
—Robert Frost (1874–1963)
“Man torturing man is a fiend beyond description. You turn a corner in the dark and there he is. You congeal into a bundle of inanimate fear. You become the very soul of anaesthesia. But there is no escaping him. It is your turn now.”
—Henry Miller (1891–1980)