Rename calc to math eval and allow it to optionally take an expression as an argument (#2195)

* Rename `calc` to `math eval` and allow it to optionally take the expression as an argument

* Moved calc tests to math eval
Also added 2 tests and changed 1 test

* Move calc docs to math eval

crates/nu-cli/src/commands/math/eval.rs

@@ -0,0 +1,107 @@
+use crate::commands::WholeStreamCommand;
+use crate::prelude::*;
+use nu_errors::ShellError;
+use nu_protocol::{Primitive, ReturnSuccess, Signature, SyntaxShape, UntaggedValue, Value};
+use nu_source::Tagged;
+
+pub struct SubCommand;
+
+#[derive(Deserialize)]
+pub struct SubCommandArgs {
+    expression: Option<Tagged<String>>,
+}
+
+#[async_trait]
+impl WholeStreamCommand for SubCommand {
+    fn name(&self) -> &str {
+        "math eval"
+    }
+
+    fn usage(&self) -> &str {
+        "Evaluate a math expression into a number"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("math eval").desc(self.usage()).optional(
+            "math expression",
+            SyntaxShape::String,
+            "the math expression to evaluate",
+        )
+    }
+
+    async fn run(
+        &self,
+        args: CommandArgs,
+        registry: &CommandRegistry,
+    ) -> Result<OutputStream, ShellError> {
+        eval(args, registry).await
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Evalulate math in the pipeline",
+            example: "echo '10 / 4' | math eval",
+            result: Some(vec![UntaggedValue::decimal(2.5).into()]),
+        }]
+    }
+}
+
+pub async fn eval(
+    args: CommandArgs,
+    registry: &CommandRegistry,
+) -> Result<OutputStream, ShellError> {
+    let name = args.call_info.name_tag.span;
+    let (SubCommandArgs { expression }, input) = args.process(registry).await?;
+
+    Ok(input
+        .map(move |x| {
+            if let Some(Tagged {
+                tag,
+                item: expression,
+            }) = &expression
+            {
+                UntaggedValue::string(expression).into_value(tag)
+            } else {
+                x
+            }
+        })
+        .map(move |input| {
+            if let Ok(string) = input.as_string() {
+                match parse(&string, &input.tag) {
+                    Ok(value) => ReturnSuccess::value(value),
+                    Err(err) => Err(ShellError::labeled_error(
+                        "Math evaluation error",
+                        err,
+                        &input.tag.span,
+                    )),
+                }
+            } else {
+                Err(ShellError::labeled_error(
+                    "Expected a string from pipeline",
+                    "requires string input",
+                    name,
+                ))
+            }
+        })
+        .to_output_stream())
+}
+
+pub fn parse<T: Into<Tag>>(math_expression: &str, tag: T) -> Result<Value, String> {
+    match meval::eval_str(math_expression) {
+        Ok(num) if num.is_infinite() || num.is_nan() => Err("cannot represent result".to_string()),
+        Ok(num) => Ok(UntaggedValue::from(Primitive::from(num)).into_value(tag)),
+        Err(error) => Err(error.to_string().to_lowercase()),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::SubCommand;
+
+    #[test]
+    fn examples_work_as_expected() {
+        use crate::examples::test as test_examples;
+
+        test_examples(SubCommand {})
+    }
+}

crates/nu-cli/src/commands/math/mod.rs

@@ -1,5 +1,6 @@
 pub mod avg;
 pub mod command;
+pub mod eval;
 pub mod max;
 pub mod median;
 pub mod min;
@@ -11,6 +12,7 @@ pub mod variance;
 
 pub use avg::SubCommand as MathAverage;
 pub use command::Command as Math;
+pub use eval::SubCommand as MathEval;
 pub use max::SubCommand as MathMaximum;
 pub use median::SubCommand as MathMedian;
 pub use min::SubCommand as MathMinimum;