Shift-Reduce Parser

Based on the current state and current input, action[ S_m , a_j ] gives one of four possible actions:

• Shift s: Shift the current input a_j onto the stack and go to the specified next state s.

• Reduce r: Given the production r: A → β , remove enough items from the stack to match β, produce output structure from those items, and put the resulting structure A back on the stack. The next state is found from the goto table.

• Accept: Parsing is completed; return top of stack as result.

• Error: The input cannot be parsed according to the grammar; call an error recovery routine. Error entries are denoted by blanks in the parsing table.