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:
“Power and violence are opposites; where the one rules absolutely, the other is absent. Violence appears where power is in jeopardy, but left to its own course it ends in power’s disappearance.”
—Hannah Arendt (1906–1975)
“I used to join the murmurings about “Where are the qualified women?” As we murmured, we would all gaze about the room, up toward the chandelier, into the corner behind the potted palm, under the napkin, hoping perhaps that qualified women would pop out like leprechauns.”
—Jane O’Reilly, U.S. feminist and humorist. The Girl I Left Behind, ch. 5 (1980)