Finch 🐦

Small, quick, sharp. A programming language on LLVM with C-like syntax, simple enough to learn in an hour and as fast as C.

🇵🇱 Polska wersja

import "math.h"

fn hypot2(float a, float b) -> float {
    return sqrt(a * a + b * b)
}

fn main() {
    name := "Finch"
    print("Hello from", name, "!")

    for i in 1..4 {
        print(i, "→", hypot2(float(i), 1.0))
    }
}

Why Finch

• Simple. No semicolons, no headers, no preprocessor. Each thing has one way to do it.
• Fast. It compiles through LLVM's -O2 pipeline to native code, with no runtime or garbage collector. Recursive fib(40) runs in about 0.19 s (clang -O2 on the same C: about 0.23 s).
• Safer than C, where it is cheap. No silent narrowing and no signed/unsigned mixing. Division by zero and null .value stop with a clear runtime error instead of undefined behavior. Operator precedence that does not bite (x & 1 == 0 means what it says).
• Errors that talk like a person:

  game.fn:3:13: error: 'y' must be i32, but this is int (use i32(...) to convert)
      3 |     i32 y = x
        |             ^
  

• Any C library, directly. import "GLFW/glfw3.h" + link "glfw", and you can call it. Headers are read by libclang, so there is nothing to declare by hand.

Quick start

Linux x86-64, LLVM 21.

git clone https://github.com/Nexoniarz/Finch.git
cd Finch
nix-shell                           # or install LLVM 21 + libclang + cmake + ninja yourself
cmake -S . -B build -G Ninja
ninja -C build

./build/finch run examples/hello.fn
./build/finch build examples/tour.fn -o tour && ./tour
tests/run.sh                        # 34 passed, 0 failed

Documentation

Pick the guide that fits you:

Guide	For	English	Polski
Beginners	Never programmed: students, seniors, anyone curious	for-beginners.md	dla-poczatkujacych.md
Technicians	Know computers, new to programming: install, whole language, C libraries, troubleshooting	for-technicians.md	dla-technikow.md
Engineers	Everything: lexer, grammar, AST, type rules, IR lowering, libclang import, ABI, internals	for-engineers.md	dla-inzynierow.md

The language at a glance

Variables	x := 5 (inferred) or int x = 5
Types	int float bool char str, sized i8…i64 u8…u64 f32 f64, pointers ptr[T] / ptr
Functions	fn add(int a, int b) -> int { return a + b }
Control	if / else if / else, while, for i in 0..10, break, continue
Pointers	p := addr(x), p.value = 5, null
Conversions	int(3.9), u8(x), float(n) (implicit only when nothing is lost)
Operators	+ - * / %, & | ^ << >> ~, == != < <= > >=, && || !
C interop	import "stdio.h", link "glfw"
Output	print(a, b, c) prints anything, separated by spaces

Examples

File	Shows
examples/hello.fn	the smallest program
examples/tour.fn	variables, functions, conditions, loops
examples/types.fn	sized numbers and pointers
examples/c_import.fn	printf, math.h, malloc/free, stderr
examples/window.fn	a GLFW + OpenGL window
examples/llvm.fn	Finch building LLVM IR through the LLVM-C API

Roadmap

• Lexer, parser, LLVM codegen, O2 optimization
• Types incl. sized integers, pointers, conversions; functions; if/while/for
• Readable compile errors; runtime checks (division, null)
• Bitwise operators with sane precedence
• C headers through libclang; link with pkg-config; link-error advice
• struct (and C structs by value)
• Arrays/slices with .len and bounds checks
• Memory: automatic free at the end of the owning block, defer, manual free when wanted
• Strings: +, len, str(x); input()
• Finch modules (import math)
• Debug info (DWARF)
• Bootstrap: the Finch compiler written in Finch

Layout

src/        compiler: lexer, parser, AST, codegen, C import, driver (C++17, ~2.4k lines)
examples/   example programs
tests/      run/ (golden output), fail/ (expected errors), run.sh
docs/       en/ and pl/ guides for three audiences

License

Apache License 2.0. Copyright 2026 Nexoniarz.