lotabout / rpn-calculator

An experimental RPN(Reverse Polish Notation) calculator

RPN(Reverse Polish Notation) Calculator

A Command-Line based RPN calculator. Main goal is to be maintainable, extensible and testable and fun.

Quick Start

$ mvn clean package
$ java -jar rpn-console-calculator/target/rpn-console-calculator-1.0-SNAPSHOT-jar-with-dependencies.jar
Type in RRNs(reverse polish notation) to start calculation, Ctrl-D to exit
4 5
stack: 4 5
2 -
stack: 4 3
sqrt
stack: 4 1.7320508075
clear
stack:

Features

• History Manipulation, could undo operations and clear stack:

  1 2 +
  stack: 3
  4 -
  stack: -1
  undo
  stack: 3 4
  5 -
  stack: 3 -1

• Easy for extending operators
  • extend ArithmeticOp class and mark it @Component and ready to go
• Properly abstracted. Easy tweaking the components for your own need. For example default implementation would show the contents on console, could easily implement Printer to send the results to HTTP responses.

Show me the code

• rpn-console-calculator: Main entry that construct and run a REPL.
  • implement console based read/write utility
  • create instances of components and wire them up.
• rpn-repl: contains the abstractions of a REPL.
  • Tokenizer will transform input string into tokens;
  • REPL itself would lookup the corresponding operators and execute them
  • operators are passed a CalcContext they can operate on
  • implement RealNumber, the main operand of operators
  • Formatter is used for formatting the context and error messages
  • Printer would be needed to print the formatted messages, be it console or HTTP responses.
  • RealNumber is built upon BigDecimal for keeping enough precisions(>=15).
• rpn-operators: pluggable package that implement operators.

ChangeLog

2021-01-16

• Segregate history management from math ops.
  • Take "memento pattern"'s idea and Context handles only save/restore snapshot, but not the undo/redo function.
  • REPL now deal with undo/redo cause the history management operators are finite and special(different from math ops).
• Tokenizer now returns tokens, not ops.

2021-01-14

• BigDecimal support. Cause double could not represents financial numbers correctly though its precision is around 15 digits.
• Use big-math library for sqrt implementation. Math.sqrt don't have enough precision.

2021-01-12

• Introduce Spring and replace SPI with Spring's @autowire.
• Realize that Operator is stateless. That means a single bean is enough, remove OperatorReaders.
• Introduce wrapper class Token that wraps positions and Operator to be executed.
• Make Context specific, because it's too complex and unnecessary to introduce generic.
• Replace RegexTokenizer with a simple space-separated one.