MiniLang Compiler

A compiler for a custom programming language — built with Flex, Bison, and C. MiniLang (.min) source files compile down to C, then to native executables.

source.min  ──►  Lexer  ──►  Parser  ──►  AST  ──►  Code Gen  ──►  C Code  ──►  Executable
             (Flex)      (Bison)               (code_gen.c)

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Features

• Three data types — num (double), str (char[1000]), bool (int)
• Arithmetic, comparison & logical operators — including %, ++x, --x
• Conditionals — when / otherwise when / otherwise / done
• Loops — fixed-count repeat n times do and repeat while
• User-defined functions with typed parameters and return values
• I/O — print and input as <type>
• 11 built-in math functions — sqrt, abs, pow, sin, cos, tan, exp, log, ceil, floor, rand
• Symbol table — duplicate-declaration and undeclared-variable detection with line numbers
• Clean C output — emitted code is human-readable and GCC-compilable

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Prerequisites

Tool	Purpose
GCC	C compiler
Flex	Lexer generator
Bison	Parser generator
Make	Build automation

# Ubuntu/Debian
sudo apt install gcc flex bison make

# macOS (Homebrew)
brew install flex bison

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Building & Usage

git clone https://github.com/commoner02/Complier-Design-MiniLang.git
cd Complier-Design-MiniLang
make clean && make

Compile a .min source file:

./minilang tests/test_basic.min

The compiler will:

1. Print the symbol table
2. Print the generated C code
3. Save test_basic.c and run it, saving output to test_basic_output.txt

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Language Reference

Data Types

Type	C Equivalent	Example
num	double	num x = 3.14
str	char[1000]	str name = "MiniLang"
bool	int (0 or 1)	bool flag = true

Variables

num x = 10
num y
y = 20
str greeting = "Hello"
bool active = true

Operators

Category	Operators
Arithmetic	+ - * / %
Comparison	== != < > <= >=
Logical	and or not
Inc / Dec	++x --x

Control Flow

when score >= 90 do
    print "A"
otherwise when score >= 80 do
    print "B"
otherwise do
    print "F"
done

Loops

# Fixed iterations
repeat 5 times do
    print "Hello"
done

# While loop
num i = 0
repeat while i < 5 do
    print i
    i = i + 1
done

Functions

func add(num a, num b) -> num do
    return a + b
done

num result = add(5, 3)
print result

Input / Output

print "Hello, World!"
print x + y

num age = input as num
str name = input as str

Built-in Math Functions

Function	Description	Example
sqrt(x)	Square root	sqrt(16) → 4
abs(x)	Absolute value	abs(-10) → 10
pow(x, y)	x raised to power y	pow(2, 3) → 8
sin(x)	Sine (radians)	sin(0) → 0
cos(x)	Cosine (radians)	cos(0) → 1
tan(x)	Tangent (radians)	tan(0) → 0
exp(x)	eˣ	exp(1) → 2.718
log(x)	Natural logarithm	log(2.718) → 1
ceil(x)	Round up	ceil(3.2) → 4
floor(x)	Round down	floor(3.8) → 3
rand()	Random number in [0, 1)	rand() → 0.456

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Example Programs

Fibonacci (first 8 terms)

num a = 0
num b = 1
num temp

repeat 8 times do
    print a
    temp = a + b
    a = b
    b = temp
done

Grade calculator

num score = 85

when score >= 90 do
    print "A"
otherwise when score >= 80 do
    print "B"
otherwise when score >= 70 do
    print "C"
otherwise do
    print "F"
done

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Running Tests

cd tests
./run_tests.sh

=========================================
         MiniLang Test Suite
=========================================

Testing: test_arithmetic     ... ✓ PASSED
Testing: test_basic          ... ✓ PASSED
Testing: test_conditional    ... ✓ PASSED
Testing: test_functions      ... ✓ PASSED
Testing: test_loops          ... ✓ PASSED
Testing: test_math_functions ... ✓ PASSED
Testing: test_strings        ... ✓ PASSED

=========================================
Results: 7 passed, 0 failed
All tests passed!
=========================================

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Error Handling

Error Type	Trigger	Example Message
Lexical	Unknown character in source	Error: unknown character '@' at line 3
Syntax	Grammar rule violation	Error: syntax error at line 7
Semantic	Undeclared variable or duplicate declaration	Error: Variable 'x' not declared at line 5

Compilation halts on any error and no C code is emitted.

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How It Works

1. Lexer (minilang.l → lex.yy.c) — Flex tokenizes source into terminals like NUM_TYPE, IDENTIFIER, WHEN, PLUS, etc.
2. Parser (minilang.y → minilang.tab.c) — Bison validates syntax via an LALR(1) grammar and builds an Abstract Syntax Tree (AST).
3. Symbol Table (symbol_table.c) — Tracks declared variables and functions; enforces scope rules during parsing.
4. Code Generator (code_gen.c) — Walks the AST and emits C into two buffers: one for user-defined functions (before main) and one for the main body.
5. Output — Both buffers are printed to stdout as a valid, self-contained C file.

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Project Structure

minilang/
├── src/
│   ├── minilang.l          # Flex lexer rules
│   ├── minilang.y          # Bison grammar + semantic actions
│   ├── ast.c / ast.h       # AST node definitions and constructors
│   ├── symbol_table.c/.h   # Variable and function symbol table
│   ├── code_gen.c/.h       # C code generation from AST
│   └── main.c              # Entry point, drives compilation
├── tests/
│   ├── run_tests.sh
│   └── test_*.min
├── Makefile
└── README.md

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License

Developed by Shuvo as a Compiler Design Laboratory assignment at Khulna University of Engineering and Technology (KUET), Department of Computer Science and Engineering.