🧮 AST Calculator

An example calculator meant to illustrate Abstract Syntax Trees (AST, https://en.wikipedia.org/wiki/Abstract_syntax_tree). This is meant to be a first look at what ASTs are and how they can be used.

Example Usage

Run the REPL:

cargo run

Sample session:

🧮 AST Calculator REPL
Enter mathematical expressions to see the AST and result.
Examples: '3 + 4 * 2', '(5 - 3) * 2.5', '-10 + 5'
Type 'quit' or 'exit' to close.

>>> 3 + 4 * 2
🌳 AST: Add(Float(3.0), Mul(Float(4.0), Float(2.0)))
✅ Result: 11

>>> (5 - 3) * 2.5
🌳 AST: Mul(Sub(Float(5.0), Float(3.0)), Float(2.5))
✅ Result: 5

>>> 8 / 0
🌳 AST: Div(Float(8.0), Float(0.0))
❌ Evaluation error: Division by zero

>>> quit
👋

Documentation

Generate docs with:

cargo doc --open

AST Visualization

How to read these trees:

• 🔵 Blue nodes (+, *, -): All mathematical operations
• 🟢 Green nodes (numbers): Leaf nodes containing actual numbers

Simple Addition: 5 + 3

flowchart TD
    A["\+"] --> B["5.0"]
    A --> C["3.0"]
    
    style A fill:#89b4fa,stroke:#cdd6f4,stroke-width:2px,color:#11111b
    style B fill:#a6e3a1,stroke:#cdd6f4,stroke-width:2px,color:#11111b
    style C fill:#a6e3a1,stroke:#cdd6f4,stroke-width:2px,color:#11111b

Evaluation: 5 + 3 = 8 (single operation)

Operator Precedence: 5 + 3 * 2

flowchart TD
    A["\+"] --> B["5.0"]
    A --> C["\*"]
    
    C --> D["3.0"]
    C --> E["2.0"]
    
    style A fill:#89b4fa,stroke:#cdd6f4,stroke-width:2px,color:#11111b
    style C fill:#89b4fa,stroke:#cdd6f4,stroke-width:2px,color:#11111b
    style B fill:#a6e3a1,stroke:#cdd6f4,stroke-width:2px,color:#11111b
    style D fill:#a6e3a1,stroke:#cdd6f4,stroke-width:2px,color:#11111b
    style E fill:#a6e3a1,stroke:#cdd6f4,stroke-width:2px,color:#11111b

Evaluation order:

1. 3 * 2 = 6 (multiplication first due to precedence)
2. 5 + 6 = 11 (then addition)

Parentheses Override Precedence: (5 + 3) * 2 - 1

flowchart TD
    A["\-"] --> B["\*"]
    A --> C["1.0"]
    
    B --> D["\+"]
    B --> E["2.0"]
    
    D --> F["5.0"]
    D --> G["3.0"]
    
    style A fill:#89b4fa,stroke:#cdd6f4,stroke-width:2px,color:#11111b
    style B fill:#89b4fa,stroke:#cdd6f4,stroke-width:2px,color:#11111b
    style D fill:#89b4fa,stroke:#cdd6f4,stroke-width:2px,color:#11111b
    style C fill:#a6e3a1,stroke:#cdd6f4,stroke-width:2px,color:#11111b
    style E fill:#a6e3a1,stroke:#cdd6f4,stroke-width:2px,color:#11111b
    style F fill:#a6e3a1,stroke:#cdd6f4,stroke-width:2px,color:#11111b
    style G fill:#a6e3a1,stroke:#cdd6f4,stroke-width:2px,color:#11111b

Evaluation order (bottom-up):

1. 5 + 3 = 8 (parentheses force addition first)
2. 8 * 2 = 16 (multiplication)
3. 16 - 1 = 15 (subtraction)