https://github.com/howardabrams/rpn-calc

A streaming calculator that computes in reverse polish notation.
https://github.com/howardabrams/rpn-calc

Last synced: 2 months ago
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A streaming calculator that computes in reverse polish notation.

• Host: GitHub
• URL: https://github.com/howardabrams/rpn-calc
• Owner: howardabrams
• License: epl-1.0
• Created: 2016-06-01T03:09:12.000Z (about 10 years ago)
• Default Branch: master
• Last Pushed: 2016-06-01T03:49:12.000Z (about 10 years ago)
• Last Synced: 2025-12-26T09:34:12.076Z (6 months ago)
• Language: Clojure
• Size: 9.77 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.org
  • License: LICENSE

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README

          
#+TITLE:  RPN Calculator

#+AUTHOR: Howard Abrams

#+EMAIL:  howard.abrams@gmail.com

#+DATE:   2016 May 15

The project answers a programming problem in [[https://gist.github.com/ckolbeck/33760242f760f6d82658][this gist]] about making a

stream calculator that calculates in reverse polish notation. While the

gist request Java, the introduction I received mentioned any language.

I hoped using Clojure would require a shorter amount of code, and a

result that was easier to read.

* Homework Problem

  Write a reverse polish notation calculator in Java. Your calculator

  should take a RPN statements composed of space separated integers

  and operators (see below) on a single line from stdin and perform

  the requested operation. In the event of unparseable input your

  program should print a sane error message to stderr and continue. If

  the result of a calculation is not a single integer your program

  should print the current state of the stack. You should include unit

  and functional tests. Please don't spend more than 2-3 hours on

  this.

  Operators:

    +

        integer addition

    -

        integer subtraction

    *

        integer multiplication

    /

        integer quotient

    %

        integer modulus

    p

        print: remove and print the top value on the stack

    d

        duplicate the value on the top of the stack

* Example Session

  #+BEGIN_EXAMPLE

    6 7 +

    13

    4 -2 * 2 *

    -16

    2 3 4 + d p *

    7

    14

    2 8 2 +

    2 10

    2 +

    Error: insufficient input for '+' operator

    2 2 r

    Error: Couldn't parse 'r' as an integer or operator

    2.5 3 +

    Error: Couldn't parse '2.5' as an integer or operator

  #+END_EXAMPLE

* Extra Credit

  Instead of taking a line at a time, accept a stream of integers and

  operators on stdin, one per line. If a line is unparseable or would

  put the stack into a bad state, print an error message, drop the bad

  input, and continue on. If the program exits due to an EOF, print

  the current state of the stack before exiting.

* Final Thoughts

  The original project required that the calculations only work with

  Integers, so I simply called out to Clojure's built-in =read-string=

  which the REPL uses to convert a =String= to other Clojure primitives,

  like =Integer=, symbols, Floats, etc.

  While the parser/tokenizer may create a =Float=, I ignore these during

  the process phase.