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Installation

This guide covers installing Desi on your system.

Prerequisites

Before installing Desi, ensure you have:

  • LLVM (version 15 or later)
  • Clang (for linking)
  • Go (version 1.21+, for building from source)
  • Windows only: Visual Studio Build Tools 2022 with the Desktop development with C++ workload (provides cl.exe and the Windows SDK used to build the C runtime)

Installation Methods

Clone the repository and build:

git clone https://github.com/desilang/desi.git
cd desi
make
./bin/desic version

git clone https://github.com/desilang/desi.git
cd desi
.\build.ps1
.\bin\desic.exe version

Verify LLVM

Desi requires LLVM for compilation. Check your LLVM version:

llc --version

clang --version

If LLVM / Clang is not installed:

brew install llvm

sudo apt install llvm clang

sudo dnf install llvm clang

Download the LLVM installer from llvm.org/releases and install it. Also install Visual Studio Build Tools with the Desktop development with C++ workload — this provides cl.exe and lib.exe for the runtime build.

Project Structure

After cloning, the Desi project has this structure:

desi/
├── bin/              # Compiled binaries
│   ├── desic         # The Desi compiler
│   ├── desifmt       # Code formatter
│   ├── desirepl      # Interactive REPL
│   └── desilsp       # Language server (for editors)
├── compiler/         # Compiler source code
│   ├── cmd/          # CLI tools
│   ├── internal/     # Compiler internals
│   ├── lib/          # Standard library (.desi files)
│   └── runtime/      # C runtime library
├── build/            # Build artifacts
│   ├── libdesi.a     # Static runtime library
│   └── output/       # Compiled executables
├── examples/         # Example programs
├── book/             # This documentation
└── docs/             # Internal documentation

Testing Your Installation

Create a simple test file:

# hello.desi
def main() -> int:
    print("Desi is working!")
    0

Run it directly:

desic run hello.desi

Or build an executable:

desic build hello.desi -o hello
./hello

You should see:

Desi is working!

The desic CLI

The Desi compiler provides subcommands for the full development workflow:

Core Commands

Command Description
desic init [name] Create a new Desi project with desi.mod
desic build [file] Build an executable
desic run [file] Build and run immediately
desic test [files] Run test files (*_test.desi)
desic check <file> Type-check without compiling

Tool Commands

Command Description
desic fmt [-w] <file\|dir> Format source code
desic doc [--all] <file> Generate documentation
desic watch [file] Watch and re-check on save
desic emit-ir <file> Emit LLVM IR to stdout
desic version Print compiler version
desic help Show all commands

Flags

Flag Description
-O2 Optimize output
-o <name> Set output executable name
-I <roots> Import roots (colon-separated)
--error-format <fmt> Error format: human or json
--color <mode> Color output: auto, always, or never

Project Mode vs File Mode

When you run desic build or desic run without a file argument, it uses the desi.mod manifest:

# File mode — compile a single file
desic run hello.desi

# Project mode — uses desi.mod entry point
cd myproject/
desic run

See First Program for a complete project walkthrough.

Troubleshooting

LLVM Not Found

If you see LLVM-related errors:

  1. Ensure LLVM is installed and in your PATH
  2. On macOS with Homebrew, you may need: 
    export PATH="/opt/homebrew/opt/llvm/bin:$PATH"
  3. On Windows, add the LLVM bin folder to your PATH: 
    C:\Program Files\LLVM\bin

Linker Errors

If linking fails:

  1. Ensure Clang is installed
  2. Check that the runtime library is built: 
    make          # macOS / Linux
.\build.ps1   # Windows

Windows: Runtime Build Fails

The Windows build script (build.ps1) requires Visual Studio Build Tools with the C++ workload. If cl.exe is not found:

  1. Install Visual Studio Build Tools
  2. Select Desktop development with C++
  3. Re-run .\build.ps1

Next Steps

Now that Desi is installed, let's write your first program!