Shift reduce parsing is a process of reducing a string to the start symbol of a grammar. Shift reduce parsing uses a stack to hold the grammar and an input tape to hold the string. Shift reduce parsing Sift reduce parsing performs the two actions: shift and reduce. That's why it is known as shift reduces parsing. At the shift action, the current symbol in the input string is pushed to a stack. At each reduction, the symbols will replaced by the non-terminals. The symbol is the right side of the production and non-terminal is the left side of the production.