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:
“Wild as it was, it was hard for me to get rid of the associations of the settlements. Any steady and monotonous sound, to which I did not distinctly attend, passed for a sound of human industry.... Our minds anywhere, when left to themselves, are always thus busily drawing conclusions from false premises.”
—Henry David Thoreau (1817–1862)
“Moving between the legs of tables and of chairs,
Rising or falling, grasping at kisses and toys,
Advancing boldly, sudden to take alarm,
Retreating to the corner of arm and knee,
Eager to be reassured, taking pleasure
In the fragrant brilliance of the Christmas tree....”
—T.S. (Thomas Stearns)