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:
“Logic and hope fade somewhat by thirty-six, when endings seem more like clear warnings than useful experience.”
—Jane O’Reilly, U.S. feminist and humorist. The Girl I Left Behind, ch. 2 (1980)
“A man who sees another man on the street corner with only a stump for an arm will be so shocked the first time he’ll give him sixpence. But the second time it’ll only be a threepenny bit. And if he sees him a third time, he’ll have him cold-bloodedly handed over to the police.”
—Bertolt Brecht (1898–1956)