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:
“La la la, Oh music swims back to me
and I can feel the tune they played
the night they left me
in this private institution on a hill.”
—Anne Sexton (1928–1974)
“Jupiter, not wanting man’s life to be wholly gloomy and grim, has bestowed far more passion than reason—you could reckon the ration as twenty-four to one. Moreover, he confined reason to a cramped corner of the head and left all the rest of the body to the passions.”
—Desiderius Erasmus (c. 1466–1536)