Left Corner

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:

    “He has left off reading altogether, to the great improvement of his originality.”
    —Charles Lamb (1775–1834)

    “O curse of marriage,
    That we can call these delicate creatures ours
    And not their appetites! I had rather be a toad,
    And live upon the vapour of a dungeon
    Than keep a corner in the thing I love
    For others’ uses.”
    —William Shakespeare (1564–1616)