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:
“When we come down into the distant village, visible from the mountain-top, the nobler inhabitants with whom we peopled it have departed, and left only vermin in its desolate streets. It is the imagination of poets which puts those brave speeches into the mouths of their heroes.”
—Henry David Thoreau (1817–1862)
“Passion is here a soilure of the wits,
We’re told, and Love a cross for them to bear;
Joy shivers in the corner where she knits
And Conscience always has the rocking-chair,
Cheerful as when she tortured into fits
The first cat that was ever killed by Care.”
—Edwin Arlington Robinson (1869–1935)