Add math tau (#7408)

# Description

Prompted by
https://discord.com/channels/601130461678272522/615329862395101194/1050693116501426216

# User-Facing Changes

New command `math tau` and endless agony whether to use `math pi` or
`math tau`

# Tests + Formatting

Example test

crates/nu-command/src/default_context.rs

@@ -419,6 +419,7 @@ pub fn create_default_context() -> EngineState {
  MathArcCosH,
  MathArcTanH,
  MathPi,
+ MathTau,
  MathEuler,
  MathLn,
  };

crates/nu-command/src/math/mod.rs

@@ -29,6 +29,7 @@ mod stddev;
 mod sum;
 mod tan;
 mod tanh;
+mod tau;
 mod utils;
 mod variance;
 
@@ -65,5 +66,6 @@ pub use arctanh::SubCommand as MathArcTanH;
 
 pub use euler::SubCommand as MathEuler;
 pub use pi::SubCommand as MathPi;
+pub use tau::SubCommand as MathTau;
 
 pub use ln::SubCommand as MathLn;

crates/nu-command/src/math/tau.rs

@@ -0,0 +1,61 @@
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{Category, Example, IntoPipelineData, PipelineData, Signature, Type, Value};
+
+#[derive(Clone)]
+pub struct SubCommand;
+
+impl Command for SubCommand {
+ fn name(&self) -> &str {
+ "math tau"
+ }
+
+ fn signature(&self) -> Signature {
+ Signature::build("math tau")
+ .input_output_types(vec![(Type::Any, Type::Float)])
+ .category(Category::Math)
+ }
+
+ fn usage(&self) -> &str {
+ "Returns the mathematical constant τ."
+ }
+
+ fn search_terms(&self) -> Vec<&str> {
+ vec!["trigonometry", "constant"]
+ }
+
+ #[allow(clippy::approx_constant)]
+ fn examples(&self) -> Vec<Example> {
+ vec![Example {
+ example: "(math tau) / 2",
+ description: "Compare π and τ",
+ result: Some(Value::test_float(std::f64::consts::PI)),
+ }]
+ }
+
+ fn run(
+ &self,
+ _engine_state: &EngineState,
+ _stack: &mut Stack,
+ call: &Call,
+ _input: PipelineData,
+ ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
+ Ok(Value::Float {
+ val: std::f64::consts::TAU,
+ span: call.head,
+ }
+ .into_pipeline_data())
+ }
+}
+
+#[cfg(test)]
+mod test {
+ use super::*;
+
+ #[test]
+ fn test_examples() {
+ use crate::test_examples;
+
+ test_examples(SubCommand {})
+ }
+}