f6033ac5af
<!-- if this PR closes one or more issues, you can automatically link the PR with them by using one of the [*linking keywords*](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword), e.g. - this PR should close #xxxx - fixes #xxxx you can also mention related issues, PRs or discussions! --> # Description <!-- Thank you for improving Nushell. Please, check our [contributing guide](../CONTRIBUTING.md) and talk to the core team before making major changes. Description of your pull request goes here. **Provide examples and/or screenshots** if your changes affect the user experience. --> Relative: #8248 After this pr, user can define const variable inside a module.  And user can export const variables, the following screenshot shows how it works (it follows https://github.com/nushell/nushell/issues/8248#issuecomment-1637442612):  ## About the change 1. To make module support const, we need to change `parse_module_block` to support `const` keyword. 2. To suport export `const`, we need to make module tracking variables, so we add `variables` attribute to `Module` 3. During eval, the const variable may not exists in `stack`, because we don't eval `const` when we define a module, so we need to find variables which are already registered in `engine_state` ## One more thing to note about the const value. Consider the following code ``` module foo { const b = 3; export def bar [] { $b } } use foo bar const b = 4; bar ``` The result will be 3 (which is defined in module) rather than 4. I think it's expected behavior. It's something like [dynamic binding](https://www.gnu.org/software/emacs/manual/html_node/elisp/Dynamic-Binding-Tips.html) vs [lexical binding](https://www.gnu.org/software/emacs/manual/html_node/elisp/Lexical-Binding.html) in lisp like language, and lexical binding should be right behavior which generates more predicable result, and it doesn't introduce really subtle bugs in nushell code. What if user want dynamic-binding?(For example: the example code returns `4`) There is no way to do this, user should consider passing the value as argument to custom command rather than const. ## TODO - [X] adding tests for the feature. - [X] support export const out of module to use. # User-Facing Changes <!-- List of all changes that impact the user experience here. This helps us keep track of breaking changes. --> # Tests + Formatting <!-- Don't forget to add tests that cover your changes. Make sure you've run and fixed any issues with these commands: - `cargo fmt --all -- --check` to check standard code formatting (`cargo fmt --all` applies these changes) - `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A clippy::needless_collect -A clippy::result_large_err` to check that you're using the standard code style - `cargo test --workspace` to check that all tests pass - `cargo run -- -c "use std testing; testing run-tests --path crates/nu-std"` to run the tests for the standard library > **Note** > from `nushell` you can also use the `toolkit` as follows > ```bash > use toolkit.nu # or use an `env_change` hook to activate it automatically > toolkit check pr > ``` --> # After Submitting <!-- If your PR had any user-facing changes, update [the documentation](https://github.com/nushell/nushell.github.io) after the PR is merged, if necessary. This will help us keep the docs up to date. --> |
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nu-cmd-lang
the base language and command crate of nu
The commands in this crate are the core commands of the nu language. It is also the base crate upon which all other command crates sit on top of including:
- nu-command
- nu-cli
- nu-cmd-dataframe
- nu-cmd-extra
As time goes on and the nu language develops further in parallel with nushell we will be adding other command crates to the system.
What does it mean to be a base crate ?
A base crate is one with minimal dependencies in our system so that other developers can come along and use this crate without having a lot of baggage in terms of other crates which will bloat their underlying application.
Background on nu-cmd-lang
This crate was designed to be a small, concise set of tools or commands that serve as the foundation layer of both nu and nushell. These are the core commands needed to have a nice working version of the nu language without all of the support that the other commands provide inside nushell. Prior to the launch of this crate all of our commands were housed in the crate nu-command. Moving forward we would like to slowly break out the commands in nu-command into different crates; the naming and how this will work and where all the commands will be located is a "work in progress" especially now that the standard library is starting to become more popular as a location for commands. As time goes on some of our commands written in rust will be migrated to nu and when this happens they will be moved into the standard library.