In contrast, LR parser

• uses rightmost derivation
• accumulates right-hand side on stack
• then decides which production to use

We look at this rightmost derivation backwards, so:

• left-to-right parsing
• rightmost derivation (when going from start, replace rightmost non-terminal)
• we display it backwards (from strings to start symbol)

Consider grammar

E ::= T | E + T
T ::= ID

ID + ID + ID
 T + ID + ID
 E + ID + ID
 E +  T + ID
 E + ID
 E +  T
 E

LR Parser looks at the largest suffix on stack that corresponds to RHS

• if found, can reduce: replace suffix on stack by non-terminal
• alternatively, can shift input symbol onto stack