Haskell GHCi Debug Adapter Phoityne installs statistics

Features

• The source file extension must be ".hs" • Can not use STDIN handle while debugging. • Creating tasks.json. • Shortcut keys • F5 : start / continue debugging • F6 : show command menu • Shift + F6 : stop watch • F7 : clean & build • F8 : start test • F9 : put a breakpoint on the current line • Shift + F9 : put a breakpoint on the current column • F10 : step next • F11 : step into

Install

Stack

Install haskell-dap, ghci-dap, haskell-debug-adapter at once.

Cabal

Install ghci-dap, haskell-debug-adapter.

Run

1. Create a project

Stack project

Cabal project

1. VSCode debug setting

2. Select a debug configuration

Stack project

Cabal project

1. Put a breakpoint

2. Start debugging

Configuration

see sample files.

.vscode/launch.json

|NAME|REQUIRED OR OPTIONAL|DEFAULT SETTING|DESCRIPTION| |:--|:--:|:--|:--| |startup|required|${workspaceRoot}/test/Spec.hs|debug startup file, will be loaded automatically.| |startupFunc|optional|"" (empty string)|debug startup function, will be run instead of main function.| |startupArgs|optional|"" (empty string)|arguments for startup function. set as string type.| |stopOnEntry|required|false|stop or not after debugger launched. |mainArgs|optional|"" (empty string)|main arguments.| |ghciPrompt|required|H>>=|ghci command prompt string.| |ghciInitialPrompt|optional|"Prelude> "|initial pormpt of ghci. set it when using custom prompt. e.g. set in .ghci| |ghciCmd|required|cabal repl -w ghci-dap --repl-no-load --builddir=${workspaceFolder/.vscode/dist-cabal-repl|launch ghci command (special value ghci-dap will use hie-bios to determine appropriate flags).| |ghciEnv|required|{}|Environment variables for ghci exectution.| |logFile|required|${workspaceRoot}/.vscode/phoityne.log|internal log file.| |logLevel|required|WARNING|internal log level.| |forceInspect|required|false|Inspect scope variables force.|

Experimental: MCP Integration

We are currently experimenting with MCP (Model Context Protocol) support for haskell-debug-adapter.

As part of this effort, we are exploring integration with pty-mcp-server, a lightweight stdio-based MCP server that enables AI-assisted control over GHCi sessions.

We have also developed a dedicated VS Code extension named pms-vscode, which provides a frontend interface to pty-mcp-server within the editor. Although haskell-debug-adapter and pms-vscode are implemented as independent extensions and operate separately, their collaboration may deepen in the future as part of broader efforts toward AI-driven and automated Haskell development tooling.

This integration aims to:

• Allow AI agents to issue debug commands over MCP to the adapter • Provide scriptable, reproducible debugging workflows • Support new development and learning experiences in interactive Haskell debugging

Demo: Haskell Debugging with cabal repl

Ref : haskell cabal debug prompt

1. Target Code Overview A function in MyLib.hs is selected to inspect its runtime state using cabal repl and an AI-driven debug interface. 2. MCP Server Initialization The MCP server is launched to allow structured interaction between the AI and the debugging commands. 3. Debugger Prompt and Environment Setup The AI receives a prompt, starts cabal repl, and loads the module to prepare for runtime inspection. 4. Debugging Execution Begins The target function is executed and paused at a predefined point for runtime observation. 5. State Inspection and Output Runtime values and control flow are displayed to help verify logic and observe internal behavior. 6. Summary Integration with pty-msp-server enables automated runtime inspection for Haskell applications.