CalcPro - Custom Formula Interpreter 📐e = ∑∞ⁿ⁼⁰ ¹ₙ🤓

CalcPro is a colourful, math-inclined single-file Java demo that implements the Interpreter Design Pattern to parse and evaluate custom formulas like ADD(5, 10), MULTIPLY(ADD(2,3),4) and DIVIDE(SUBTRACT(20,4),2). It also supports variables via a Context (e.g., x = 5).

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🚀 Highlights

• Clean AST-based interpreter: each operation is an Expression implementation (Add, Subtract, Multiply, Divide, …).
• Operator registry — register new operators (e.g., POWER) without touching parser code.
• Interactive Swing GUI: colourful header, math doodles, variables panel and instant evaluation.
• Simple, single-file implementation ideal for learning, prototyping, or extending.

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📁 Repository

GitHub: https://github.com/Tharindu714/CalcPro-Custom-Formula-Interpreter

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🧪 Quick demo (console outputs)

• ADD(5, 10) → 15.0
• MULTIPLY(ADD(2, 3), 4) → 20.0
• DIVIDE(SUBTRACT(20, 4), 2) → 8.0
• MULTIPLY(ADD(x, 3), 2) with x = 5 → 16.0

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🛠️ Build & Run

1. Ensure you have Java (JDK 8+) installed.
2. Clone the repo:

git clone https://github.com/Tharindu714/CalcPro-Custom-Formula-Interpreter.git
cd CalcPro-Custom-Formula-Interpreter

3. Compile & run the single Java file (it's included at the root):

javac CalcPro_Interpreter_GUI.java
java CalcPro_Interpreter_GUI

The app prints demo outputs to the console and opens the colourful CalcPro GUI.

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🧠 Design overview (Interpreter pattern)

• Expression (interface) — exposes double interpret(Context ctx).
• Terminal expressions — NumberExpression, VariableExpression.
• Non-terminal (composite/binary) — BinaryExpression (left/right) with subclasses AddExpression, SubtractExpression, MultiplyExpression, DivideExpression, PowerExpression.
• Context — holds variable name/value map and resolves variables at runtime.
• FormulaParser — parses strings into an AST, handles nested function calls and top-level comma splitting.
• OperatorRegistry — maps operation names (ADD, POWER) to small factory lambdas that build Expression objects.

This separation keeps the parser stable while new functionality is added by registering new expression creators.

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✨ Adding a new operator (example: POWER)

1. Create the expression (already present in code as PowerExpression):

class PowerExpression extends BinaryExpression {
    public PowerExpression(Expression left, Expression right) { super(left, right); }
    @Override
    public double interpret(Context ctx) throws Exception {
        return Math.pow(left.interpret(ctx), right.interpret(ctx));
    }
}

2. Register it in OperatorRegistry (one line):

OperatorRegistry.register("POWER", args -> {
    requireArgCount("POWER", args, 2);
    return new PowerExpression(args.get(0), args.get(1));
});

No parser changes required — just class + registry entry.

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📐 UML (PlantUML) — Class Diagram & Sequence Diagram

Class Diagram (PlantUML)

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Sequence Diagram (PlantUML)

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🖼️ Scenario

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✅ Contribution

Contributions welcome — fork the repo, add operators, file issues, or submit PRs. If you add interesting operators (TRIG, LOG, SUM over lists), please include tests and example formulas.

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📜 License

MIT — feel free to reuse and adapt.

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Created with ❤️ for learners and tinkers — Tharindu's CalcPro demo.