Calculator REPL

Description

A simple calculator application that performs basic arithmetic operations in a REPL.

This calculator supports basic arithmetic operations (+, -, *, / ^, %) and combinations of these operations using parentheses ((1 + 2) * 3) to change the order of operations, otherwise the default precedence is used. The application also supports history tracking for the last 3 expressions. These values can be referenced using (p1, p2, p3) in an expression.

This project is an artifact of my Clojure learning journey. As a learning project, this application is not intended to be a complete, fully functional calculator. It is intended to be used as a tool for me to practice building practical applications in Clojure. I would appreciate any constructive feedback. If you have any suggestions or feedback, please feel free to open an issue.

This project is still a work in progress and I will continue to improve it.

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Objectives

1. Apply knowledge of Clojure syntax, functions, and collections to build a practical project.
2. Gain experience structuring a Clojure project and implementing core arithmetic functions.
3. Practice user input handling, function composition, and error handling.
4. Practice building a simple REPL.

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Functional Requirements

1. Basic Arithmetic Operations:
   • Support for addition, subtraction, multiplication, and division.
   • Division by zero should be handled gracefully with an appropriate error message.
2. User Input Handling:
   • Collect user input for numbers and an operation (+, -, *, /, ^, %).
   • Validate input to ensure it's either a valid number or operation symbol.
   • Provide feedback for invalid inputs.
3. Calculator Logic:
   • Perform the chosen arithmetic operation on the input numbers and display the result.
   • Include error handling for invalid inputs and invalid operations.
4. REPL Operation:
   • The calculator should run in a loop, continuously accepting input until a stop command is given.
   • The stop commands will be "quit" or "exit", which the user can type to stop the program.
5. (Stretch Goal 1) Expression Parsing:
   • Support for user input of more complex expressions, allowing users to input expressions like 1 + 2 * 3 or (1 + 2) * 3.
   • Expressions are parsed into an AST before being evaluated.
   • Provide error handling for malformed or invalid expressions.
6. (Stretch Goal 2) History Tracking:
   • Support for tracking the user's last 3 evaluated expressions.
   • Add additional syntax for the REPL to allow users to reference and use the tracked values in new expressions.

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Non-Functional Requirements

1. User Interface:
   • Provide a simple command-line interface that allows the user to perform basic arithmetic operations.
2. Error Handling:
   • Ensure the application handles errors gracefully, providing helpful messages for invalid inputs or operations.
3. Project Structure:
   • Maintain a clean and organized Clojure project structure, separating user input, calculations, and expression evaluation logic.

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Testing

1. Unit Testing:
   • Test the arithmetic functions with valid and invalid inputs (e.g., division by zero).
2. Integration Testing:
   • Test the continuous operation of the calculator by simulating various inputs, including numbers, operations, and stop commands.
3. Edge Case Handling:
   • Ensure the program handles invalid inputs, malformed expressions, and invalid commands appropriately, with clear error messages.

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Future Work

1. Expand the functionality of the calculator to support more advanced arithmetic operations and expression parsing.
2. Add support for optionally reading user input from a file or other source.
3. Add better logging and error reporting.
4. Add better handling for exiting the application.

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References

1. Crafting Interpreters
   • Specifically chapters 4 - 7
2. Clojure Docs
3. Clojure Defmulti and Defmethod

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Special Thanks

A special thanks to the memebers of the Clojure Camp community. They do amazing work for the Clojure community and their feedback has been greatly appreciated.