nix-super/doc/manual/rl-next/repl-doc-renders-doc-comments.md

synopsis	significance	issues	prs
`nix-repl`'s `:doc` shows documentation comments	significant	3904 10771	1652 9054 11072

nix repl has a :doc command that previously only rendered documentation for internally defined functions. This feature has been extended to also render function documentation comments, in accordance with RFC 145.

Example:

nix-repl> :doc lib.toFunction
Function toFunction
    … defined at /home/user/h/nixpkgs/lib/trivial.nix:1072:5

    Turns any non-callable values into constant functions. Returns
    callable values as is.

Inputs

    v

      : Any value

Examples

    :::{.example}

## lib.trivial.toFunction usage example

      | nix-repl> lib.toFunction 1 2
      | 1
      | 
      | nix-repl> lib.toFunction (x: x + 1) 2
      | 3

    :::

Known limitations:

• It currently only works for functions. We plan to extend this to attributes, which may contain arbitrary values.
• Some extensions to markdown are not yet supported, as you can see in the example above.

We'd like to acknowledge Yingchi Long for proposing a proof of concept for this functionality in #9054, as well as @sternenseemann and Johannes Kirschbauer for their contributions, proposals, and their work on RFC 145.