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:
“Had I but died an hour before this chance
I had lived a blessed time; for from this instant
There’s nothing serious in mortality.
All is but toys. Renown and grace is dead;
The wine of life is drawn, and the mere lees
Is left this vault to brag of.”
—William Shakespeare (1564–1616)
“Many said selfishness was the flaw of our modern age; but then self-conceit emerged from a corner of the deepest hell to join selfishness.”
—Franz Grillparzer (1791–1872)