Scheme Interpreter in C

A complete Scheme programming language interpreter built from scratch in C. This interpreter can parse, evaluate, and execute Scheme code with support for functions, variables, arithmetic, and list operations.

Features

It can execute the following constructs:

1. Lambda functions
2. In-place lambda function calls
3. define
4. Arithmetic + - * / operations
5. Logical operations and and or
6. if/else
7. List functions: car, cdr, cons, map, append
8. List description without execution: ‘(1 2 3)
9. Execution functions: apply, eval
10. Recursive function execution
11. Helper functions: null?, length
12. equal?
13. load

How to Use

Compile and Run

gcc -o scheme interpreter.c
./scheme

Memory Management

The interpreter handles memory allocation and cleanup automatically.

How It Works

The interpreter processes code in three stages:

1. Tokenization: Breaks input into pieces (numbers, symbols, parentheses)
2. Parsing: Builds a tree structure from tokens
3. Evaluation: Executes the parsed code

Testing

Run the included test suite:

> (load "tests.scm")

The test file demonstrates all supported features with working examples.

Technical Details

Implementation

• Language: Pure C (no external dependencies)
• Memory: Dynamic allocation with cleanup

Supported Scheme Features

• Lambda functions and closures
• Recursive function calls
• Proper list handling
• String parsing with escape sequences
• Multiple number types (int, float, rational)
• File loading and execution

File Structure

The main interpreter file contains:

• Token handling (TokenList, tokenize_input)
• Data types (data struct with union for different types)
• Environment management (Env, lookup, add_elements_to_environment)
• Parser (parse_func, parse)
• Evaluator (eval function)
• Built-in functions (cons_builtin, car_builtin, etc.)