How can you explain reverse polish notation in simple words?

Answer 1

Reverse Polish Notation (RPN) is a system where expressions are evaluated from left to right, with no precedence, with operators stated following the operands. A typical RPN expression might be ab+c*, which in infix means (a+b)*c. (Infix is our "standard" system which we use when writing programs) Note that the infix expression required parenthesis to override operator precedence, but the RPN expression did not. If you said in infix a+b*c, the RPN equivalent would be abc*+. The value of RPN is that it is easy to build a stack machine that processes the expression. Each time you encounter an operand, you push it on the stack. Each time you encounter an operator, you process it, replacing the top two elements of the stack with the result (for binary operators), or replacing the top element of the stack with the result (for unary operators). RPN is often used in compiler design.

Answer 2

Reverse polish notation is a notation where expressions are evaluated from left to right. It is called reverse polish notation because it is the reverse of polish notation, which was invented in 1920 by the Polish mathematician Jan Łukasiewicz. Operands are stated first, followed by operators. (In polish notation, operators are first.)

There are no parenthesis, and there is no operator precedence. The only limitation is that operator arity, such as unary, binary, ternary, etc. must be defined distinctly, i.e. the unary minus is not the same as binary minus, and must be recognized as such.

Typical implementation...

When an operand is encountered, it is pushed on the stack. When an operator is encountered it acts on the top one or two elements of the stack and replaces them.

Some examples...

a + b * c is expressed as ab*+
(a + b) * c is expressed as ab+c*
a + b * c + d is expressed as abc*d++
a * b + c * d is expressed as ab*cd*+
a * - b is expressed as ab-* where - is unary, not binary