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:
“Nearing again the legendary isle
Where sirens sang and mariners were skinned,
We wonder now what was there to beguile
That such stout fellows left their bones behind.”
—Cecil Day Lewis (1904–1972)
“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)