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:
“I cannot trust myself to put in words what I feel at this time. Every kind thought that is in your minds and every good wish that is in your hearts for me finds its responsive wish and thought in my mind and heart for each of you. I love this city. It has been my own cherished home. Twice before I have left it to discharge public duties and returned to it with gladness, as I hope to do again.”
—Benjamin Harrison (1833–1901)
“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)