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:

    “Ae spring brought off her master hale,
    But left behind her ain grey tail:”
    —Robert Burns (1759–1796)

    “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)