This adds support for (limited) mutable variables. Mutable variables are created with mut much the same way immutable variables are made with let.
Mutable variables allow mutation via the assignment operator (=).
❯ mut x = 100
❯ $x = 200
❯ print $x
200
Mutable variables are limited in that they're only tended to be used in the local code block. Trying to capture a local variable will result in an error:
❯ mut x = 123; {|| $x }
Error: nu::parser::expected_keyword (link)
× Capture of mutable variable.
The intent of this limitation is to reduce some of the issues with mutable variables in general: namely they make code that's harder to reason about. By reducing the scope that a mutable variable can be used it, we can help create local reasoning about them.
Mutation can occur with fields as well, as in this case:
❯ mut y = {abc: 123}
❯ $y.abc = 456
❯ $y
On a historical note: mutable variables are something that we resisted for quite a long time, leaning as much as we could on the functional style of pipelines and dataflow. That said, we've watched folks struggle to work with reduce as an approximation for patterns that would be trivial to express with local mutation. With that in mind, we're leaning towards the happy path.
* attempts to add `div` math operator
* allows `//` to be used too
* fmt:
* clippy issue
* returns appropriate type
* returns appropriate type 2
* fmt
* ensure consistency; rename to `fdiv`
* Update parser.rs
* input and output tests
* input and output types for dfr
* expression converter
* remove deprecated command
* correct expressions
* cargo clippy
* identifier for ls
* cargo clippy
* type for head and tail expression
* modify full cell path if block
* change between lazy and eager
* when expressions
* examples for aggregations
* more examples for agg
* examples for dataframes
* checked examples
* cargo fmt
* lazyframe definition
* expressions and lazy frames
* new alias expression
* more expression commands
* updated to polars main
* more expressions and groupby
* more expressions, fetch and sort-by
* csv reader
* removed open csv
* unique function
* joining functions
* join lazy frames commands with eager commands
* corrected tests
* Update .gitignore
* Update .gitignore
Co-authored-by: JT <547158+jntrnr@users.noreply.github.com>
