Mini Compiler

A compiler for a custom language built from scratch in pure Python — no external libraries.

Implements the full compiler pipeline:

• Lexer — tokenizes raw source text
• Parser — builds an Abstract Syntax Tree using recursive descent
• Semantic Analyzer — catches errors before execution (undeclared variables, division by zero)
• Interpreter — tree-walk evaluator that executes the AST

Language Features

• Variables and arithmetic (+, -, *, /)
• String concatenation
• if / else
• while loops
• print statements
• Comparisons (==, !=, <, >, <=, >=)
• Comments with #
• Floats and booleans

Usage

python main.py program.mini          # run a file
python main.py --debug program.mini  # show tokens + AST + output
python main.py --repl                # interactive mode

Example

x = 10
y = 3
result = x + y * 2
print result

if result > 15
    print "big"
else
    print "small"

Output:

16
big