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:

    “If you’re going to burn, burn.
    If you’re going to boil, boil
    and if you’re breaking, O Heart,
    go ahead and break,
    for I’ve just left him,
    that no-good man.”
    —Hla Stavhana (c. 50 A.D.)

    “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)