Install

Fels runs on 64-bit Windows and Linux, and builds programs for both. The latest release has a download for each.

Windows

1. Download fels-<version>-x86_64-windows.zip from the latest release.
2. Unpack it and run install.ps1 in that folder. It copies Fels to %LOCALAPPDATA%\fels and puts it on your PATH.
3. Open a new terminal and type fels version to check that it works.

Linux

1. Download fels-<version>-x86_64-linux.tar.gz and unpack it.
2. Run ./install.sh in that folder. It copies Fels to ~/.fels and puts it on your PATH.
3. Open a new terminal and type fels version.

Fels needs the C++ runtime of GCC 11 or newer (Ubuntu 22.04, Debian 12, Fedora 35 and later).

Editor

fels lsp is a language server: errors as you type, completion, hover and go to definition.

• Zed: install the Fels extension. It adds run buttons beside main and each test.
• Other editors: point your LSP client at fels lsp, and use the tree-sitter grammar for highlighting.

Building Fels yourself

The compiler is written in Zig 0.16. You need an LLVM build that includes its C headers: on Linux, llvm.org’s release (LLVM-22.1.6-Linux-X64.tar.xz, which the build links statically), on Windows clang+llvm-22.1.6-x86_64-pc-windows-msvc.tar.xz.

zig build -Dllvm-path=path/to/llvm
zig build test -Dllvm-path=path/to/llvm

The compiler lands in zig-out/bin.

Stuck? Ask in #help on the Fels Discord.

Next: your first program.