mirror of
https://github.com/nushell/nushell.git
synced 2024-10-16 23:33:49 +02:00
fa2e6e5d53
<!--
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.
-->
> [!NOTE]
> This PR description originally used examples where the `generator`
closure returned a list. It has since been updated to use records
instead.
The `unfold` command allows users to dynamically generate streams of
data. The stream is generated by repeatedly invoking a `generator`
closure. The `generator` closure accepts a single argument and returns a
record containing two optional keys: 'out' and 'next'. Each invocation,
the 'out' value, if present, is added to the stream. If a 'next' key is
present, it is used as the next argument to the closure, otherwise
generation stops.
The name "unfold" is borrowed from other functional-programming
languages. Whereas `fold` (or `reduce`) takes a stream of values and
outputs a single value, `unfold` takes a single value and outputs a
stream of values.
### Examples
A common example of using `unfold` is to generate a fibbonacci sequence.
See
[here](6ffdac103c/src/sources.rs (L65))
for an example of this in rust's `itertools`.
```nushell
> unfold [0, 1] {|fib| {out: $fib.0, next: [$fib.1, ($fib.0 + $fib.1)]} } | first 10
───┬────
0 │ 0
1 │ 1
2 │ 1
3 │ 2
4 │ 3
5 │ 5
6 │ 8
7 │ 13
8 │ 21
9 │ 34
───┴────
```
This command is particularly useful when consuming paginated APIs, like
Github's. Previously, nushell users might use a loop and buffer
responses into a list, before returning all responses at once. However,
this behavior is not desirable if the result result is very large. Using
`unfold` avoids buffering and allows subsequent pipeline stages to use
the data concurrently, as it's being fetched.
#### Before
```nushell
mut pages = []
for page in 1.. {
let resp = http get (
{
scheme: https,
host: "api.github.com",
path: "/repos/nushell/nushell/issues",
params: {
page: $page,
per_page: $PAGE_SIZE
}
} | url join)
$pages = ($pages | append $resp)
if ($resp | length) < $PAGE_SIZE {
break
}
}
$pages
```
#### After
```nu
unfold 1 {|page|
let resp = http get (
{
scheme: https,
host: "api.github.com",
path: "/repos/nushell/nushell/issues",
params: {
page: $page,
per_page: $PAGE_SIZE
}
} | url join)
if ($resp | length) < $PAGE_SIZE {
{out: $resp}
} else {
{out: $resp, next: ($page + 1)}
}
}
```
# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->
- An `unfold` generator is added to the default context.
# 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` to
check that you're using the standard code style
- `cargo test --workspace` to check that all tests pass (on Windows make
sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- `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.
-->
Given the complexity of the `generator` closure's return value, it would
be good to document the semantics of `unfold` and provide some in-depth
examples showcasing what it can accomplish.
120 lines
1.5 KiB
Rust
120 lines
1.5 KiB
Rust
mod alias;
|
|
mod all;
|
|
mod any;
|
|
mod append;
|
|
mod assignment;
|
|
mod break_;
|
|
mod cal;
|
|
mod cd;
|
|
mod compact;
|
|
mod config_env_default;
|
|
mod config_nu_default;
|
|
mod continue_;
|
|
mod conversions;
|
|
mod cp;
|
|
mod date;
|
|
mod def;
|
|
mod default;
|
|
mod detect_columns;
|
|
mod do_;
|
|
mod drop;
|
|
mod each;
|
|
mod echo;
|
|
mod empty;
|
|
mod error_make;
|
|
mod every;
|
|
#[cfg(not(windows))]
|
|
mod exec;
|
|
mod export_def;
|
|
mod fill;
|
|
mod find;
|
|
mod first;
|
|
mod flatten;
|
|
mod for_;
|
|
#[cfg(feature = "extra")]
|
|
mod format;
|
|
mod get;
|
|
mod glob;
|
|
mod group_by;
|
|
mod hash_;
|
|
mod headers;
|
|
mod help;
|
|
mod histogram;
|
|
mod insert;
|
|
mod inspect;
|
|
mod into_datetime;
|
|
mod into_filesize;
|
|
mod into_int;
|
|
mod join;
|
|
mod last;
|
|
mod length;
|
|
mod let_;
|
|
mod lines;
|
|
mod loop_;
|
|
mod ls;
|
|
mod match_;
|
|
mod math;
|
|
mod merge;
|
|
mod mkdir;
|
|
mod move_;
|
|
mod mut_;
|
|
mod network;
|
|
mod nu_check;
|
|
mod open;
|
|
mod par_each;
|
|
mod parse;
|
|
mod path;
|
|
mod platform;
|
|
mod prepend;
|
|
mod print;
|
|
#[cfg(feature = "sqlite")]
|
|
mod query;
|
|
mod random;
|
|
mod range;
|
|
mod redirection;
|
|
mod reduce;
|
|
mod reject;
|
|
mod rename;
|
|
mod return_;
|
|
mod reverse;
|
|
mod rm;
|
|
#[cfg(feature = "extra")]
|
|
mod roll;
|
|
#[cfg(feature = "extra")]
|
|
mod rotate;
|
|
mod run_external;
|
|
mod save;
|
|
mod select;
|
|
mod semicolon;
|
|
mod seq;
|
|
mod seq_char;
|
|
mod skip;
|
|
mod sort;
|
|
mod sort_by;
|
|
mod source_env;
|
|
mod split_by;
|
|
mod split_column;
|
|
mod split_row;
|
|
mod str_;
|
|
mod table;
|
|
mod take;
|
|
mod to_text;
|
|
mod touch;
|
|
mod transpose;
|
|
mod try_;
|
|
mod ucp;
|
|
mod unfold;
|
|
mod uniq;
|
|
mod uniq_by;
|
|
mod update;
|
|
mod upsert;
|
|
mod url;
|
|
mod use_;
|
|
mod where_;
|
|
#[cfg(feature = "which-support")]
|
|
mod which;
|
|
mod while_;
|
|
mod with_env;
|
|
mod wrap;
|
|
mod zip;
|