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:
“Therefore when thou doest thine alms, do not sound a trumpet before thee, as the hypocrites do in the synagogues and in the streets, that they may have glory of men. Verily I say unto you, they have their reward. But when thou doest alms, let not thy left hand know what thy right hand doeth.”
—Bible: New Testament Matthew 6:2-3.
The Sermon on the Mount.
“The arbitrary division of one’s life into weeks and days and hours seemed, on the whole, useless. There was but one day for the men, and that was pay day, and one for the women, and that was rent day. As for the children, every day was theirs, just as it should be in every corner of the world.”
—Alice Caldwell Rice (1870–1942)