Reverse Polish Notation (RPN) Calculator

The calculator has a stack that can contain real numbers.

• The calculator waits for user input and expects to receive strings containing whitespace separated lists of numbers and operators.

• Numbers are pushed on to the stack. Operators operate on numbers that are on the stack. • Available operators are +, -, *, /, sqrt, undo, clear.

• Operators pop their parameters off the stack, and push their results back onto the stack.

• The ‘clear’ operator removes all items from the stack.

• The ‘undo’ operator undoes the previous operation. “undo undo” will undo the previo us two operations.

• sqrt performs a square root on the top item from the stack.

• The ‘+’, ‘-’, ‘*’, ‘/’ operators perform addition, subtraction, multiplication and division respectively on the top two items from the stack.

• After processing an input string, the calculator displays the current contents of the stack as a space-separated list.

• Numbers should be stored on the stack to at least 15 decimal places of precision, but displayed to 10 decimal places (or less if it causes no loss of precision).

• All numbers should be formatted as plain decimal strings (ie. no engineering formatting).

• If an operator cannot find a sufficient number of parameters on the stack, a warning is displayed: operator (position: ): insufficient parameters

• After displaying the warning, all further processing of the string terminates and the current state of the stack is displayed.

Ideas behind the design

• I was trying to be as expressive in code as possible, by naming things according to domain terms and project requirements like: SorryCannotFindSufficientNumberOfParametersInTheStack , Operation.performOperationAndAddResultToStack(), etc., to make the code as clear as possible for those who understand the domain
• I was trying to follow Hexagonal/DDD approach, by splitting the whole project to domain, application and infrastructure layers
• infrastructure layer contains only CLI interface, but later on — will be able to support also web interface
• All the calculator logic is contained in the domain layer, and adding a new operation shall not involve anything from application or infrastructure layers

Install

git clone [email protected]:ibudasov/rpn-calculator.git

Use

MainKt.main 👈 run it in your IDE 💁‍

Todo

• preserve stack between inputs, so the operations can be chained