Haskell Debug Adapter for Zed

A Zed extension that enables debugging Haskell applications using haskell-debug-adapter.

Prerequisites

Install haskell-debug-adapter and ensure it's in your $PATH:

cabal install haskell-dap ghci-dap haskell-debug-adapter

Installation

1. Open Zed editor

2. Install the dev extension:

   • Press Cmd+Shift+P (macOS) or Ctrl+Shift+P (Linux/Windows)
   • Type and select: zed: install dev extension
   • Choose this extension folder

3. Configure debug settings:

   • Create .zed/debug.json in your project root
   • Copy the example configuration from example/debug.json

Configuration Example

Create .zed/debug.json with:

[
  {
    "adapter": "Haskell",
    "label": "Haskell debugger",
    "name": "Haskell debugger",
    "type": "ghc",
    "request": "launch",
    "cwd": "$ZED_WORKTREE_ROOT",
    "startup": "$ZED_WORKTREE_ROOT/app/Main.hs",
    "workspace": "$ZED_WORKTREE_ROOT",
    "logFile": "$ZED_WORKTREE_ROOT/.zed/haskell-debug.log",
    "ghciCmd": "cabal repl <your-binary-name> -w ghci-dap --repl-no-load",
    "logLevel": "INFO",
    "startupFunc": "main",
    "startupArgs": "",
    "stopOnEntry": true,
    "mainArgs": "",
    "ghciPrompt": "H>>= ",
    "ghciInitialPrompt": "> ",
    "ghciEnv": {},
    "forceInspect": false
  }
]

Important: Replace <your-binary-name> in ghciCmd with your actual executable name from your .cabal file.

Usage

1. Open your Haskell project in Zed
2. Set breakpoints in your code
3. Press F5 or run debug: start from command palette
4. Select "Haskell debugger"

Voilà, let's debug!

Troubleshooting

If debugging doesn't start:

• Verify haskell-debug-adapter is in your PATH: which haskell-debug-adapter
• Check the log file at .zed/haskell-debug.log
• View Zed logs: Cmd+Shift+P → zed: open log