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)
“Good Lord, for alliance! Thus goes every one to the world but I, and I am sunburnt; I may sit in a corner and cry “Heigh-ho for a husband!””
—William Shakespeare (1564–1616)