A pushdown automaton is a way to implement a context-free grammar in a similar way we design DFA for a regular grammar. A DFA can remember a finite amount of information, but a PDA can remember an infinite amount of information. This part has been taken from   TutorialsPoint . This example shows how PDA's yields notation and parse tree notation are done step-by-step. This language accepts the expression 0*1(0+1)*