Conjure NFNL Error: Macro Evaluation With Local Function

by Alex Johnson 57 views

This article addresses a peculiar issue encountered when using Conjure, a Neovim interactive development tool, with Fennel code that involves macros. Specifically, the problem arises when evaluating a macro that contains a locally defined function. This situation leads to an error within Conjure's NFNL (Neovim Fennel) client, disrupting the development workflow. Let's dive into the details, potential causes, and a reproducible example to understand this issue better.

Understanding the Issue

When evaluating Fennel code that utilizes macros, and these macros internally define local functions, Conjure throws an error. The error message typically looks like this:

; --------------------------------------------------------------------------------
; eval (buf): <path-omitted>/src/app.fnl
; [Compile] .../.config/nvim/bundle/conjure/lua/conjure/nfnl/fennel.lua:1069: attempt to index field 'options' (a nil value)

This error points to a specific line in fennel.lua within Conjure's NFNL implementation. The suspicion is that Conjure's initialization of the Fennel environment is somehow getting mixed up, possibly due to the use of autoload in either Conjure or NFNL. The core issue seems to be that the options field within the Fennel environment hasn't been properly defined or initialized when the macro is evaluated.

Reproducing the Error

To illustrate the problem, consider the following minimal example. This setup requires both nfnl.module and the following file structure:

❯ tree -a
.
├── .nfnl.fnl
└── src
    ├── app.fnl
    ├── app.lua
    └── macros.fnlm

2 directories, 4 files

Here are the contents of each file:

  • .nfnl.fnl:

    {:source-file-patterns ["src/*.fnl"]}

  • src/macros.fnlm:

    (fn foo []
  ;; Evaluating src/app.fnl in Conjure will succeed if this next line is removed
  (fn dummy [] nil)
  true)

{: foo}

  • src/app.fnl:

    (import-macros m :src.macros)

(local {: define} (require :nfnl.module))

(local M (define :src.app))

(fn M.test []
  (m.foo))

M

In this setup, if you evaluate src/app.fnl in Conjure, it will likely fail with the aforementioned error. However, if you comment out the (fn dummy [] nil) line within src/macros.fnlm, restart Neovim, and then evaluate src/app.fnl, it will succeed. Interestingly, after this initial success, you can uncomment the dummy function, and subsequent evaluations might continue to succeed, but the macro updates don't propagate as expected.

For instance, if you modify src/macros.fnlm to:

(fn foo []
  (fn dummy [] nil)
  (dummy))

{: foo}

And then re-evaluate src/app.fnl, evaluating (M.test) still returns true from the original version of src/macros.fnlm rather than nil, indicating that the macro hasn't been updated in the evaluated environment.

Potential Causes

Several factors could be contributing to this issue:

  1. Initialization Order: The order in which Conjure initializes the Fennel environment and loads macros might be critical. If macros containing local functions are evaluated before the environment is fully set up, it could lead to the options field being undefined.
  2. Autoloading Issues: The use of autoload in either Conjure or NFNL might be causing unexpected delays or race conditions in the loading and initialization process.
  3. Macro Caching: Conjure might be caching the macro definitions in a way that prevents updates from propagating correctly after the initial error. This could explain why subsequent evaluations succeed but don't reflect the latest changes.
  4. NFNL Integration: The integration between Conjure and NFNL might have specific edge cases that aren't being handled correctly, particularly when dealing with macros and local functions.

Diagnosing the Problem

To further diagnose this issue, consider the following steps:

  • Examine Conjure's Initialization: Investigate how Conjure initializes the Fennel environment and loads macros. Pay close attention to the order of operations and any potential dependencies.
  • Check Autoloading Behavior: Analyze the autoloading behavior of both Conjure and NFNL to identify any potential conflicts or delays.
  • Inspect Macro Caching: Determine how Conjure caches macro definitions and whether this caching mechanism is interfering with updates.
  • Review NFNL Integration: Carefully review the integration between Conjure and NFNL, looking for any specific code paths that might be causing the error.

Possible Solutions

Based on the potential causes, here are some possible solutions:

  1. Adjust Initialization Order: Modify Conjure's initialization process to ensure that the Fennel environment is fully set up before macros are evaluated.
  2. Optimize Autoloading: Fine-tune the autoloading behavior of Conjure and NFNL to avoid race conditions or delays.
  3. Improve Macro Caching: Implement a more robust macro caching mechanism that allows for updates to propagate correctly.
  4. Enhance NFNL Integration: Address any specific issues in the integration between Conjure and NFNL that might be causing the error.

Workarounds

In the meantime, here are some workarounds that might help:

  • Restart Neovim: Restarting Neovim can sometimes clear the cached macro definitions and allow for updates to propagate correctly.
  • Evaluate Macros Manually: Instead of relying on Conjure to automatically evaluate macros, try evaluating them manually using the :ConjureEval command.
  • Simplify Macros: Avoid using local functions within macros if possible, as this seems to be the trigger for the error.

Impact on Development

This issue can significantly impact the development workflow when using Conjure with Fennel, especially when working with complex macros that define local functions. The error can be disruptive, and the inability to propagate macro updates can lead to unexpected behavior and debugging challenges. Addressing this issue is crucial for improving the overall development experience.

Community Discussion

This problem has been discussed within the Fennel and Conjure communities, with users sharing their experiences and potential workarounds. It's essential for developers to stay informed about these discussions and contribute their own findings to help resolve the issue.

Conclusion

The Conjure NFNL client error when evaluating macros containing local functions is a complex issue that requires careful investigation and a multi-faceted approach to resolve. By understanding the potential causes, diagnosing the problem, and implementing appropriate solutions, developers can overcome this challenge and enjoy a smoother development experience with Conjure and Fennel. This article has provided a comprehensive overview of the issue, potential causes, and possible solutions, empowering developers to tackle this problem effectively. The continued effort from the community will be essential to improve Conjuire NFNL client and create a seamless user experience with Fennel code.

For more information on Conjure, you can visit the official Conjure GitHub Repository. This repository is an excellent resource for updates, documentation, and community discussions.