starting to build this

crates/nu-command/src/lib.rs

@@ -8,6 +8,7 @@ mod filesystem;
 mod filters;
 mod formats;
 mod strings;
+mod math;
 mod system;
 mod viewers;
 
@@ -21,5 +22,6 @@ pub use filesystem::*;
 pub use filters::*;
 pub use formats::*;
 pub use strings::*;
+pub use math::*;
 pub use system::*;
 pub use viewers::*;

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

@@ -0,0 +1,60 @@
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EvaluationContext};
+use nu_protocol::{Example, ShellError, Signature, Span, Type, Value};
+
+pub struct SubCommand;
+
+impl Command for SubCommand {
+    fn name(&self) -> &str {
+        "math abs"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("math abs")
+    }
+
+    fn usage(&self) -> &str {
+        "Returns absolute values of a list of numbers"
+    }
+
+    fn run(&self, context: &EvaluationContext, call: &Call, input: Value) -> Result<Value, ShellError> {
+        let mapped = input.map(move |val| match val.value {
+            Value::Int { val, span } => Value::int(val.abs(), span),
+            Value::Float { val, span } => Value::Float{val: val.abs(), span: span},
+            Value::Duration { val, span } => Value::Duration{val: val.abs(), span: span},
+            other => abs_default(other)?,
+        });
+        Ok(mapped)
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Get absolute of each value in a list of numbers",
+            example: "echo [-50 25] | math abs",
+            result: Some(vec![
+                Value::test_int(50),
+                Value::test_int(25),
+            ]),
+        }]
+    }
+}
+
+fn abs_default(_: Value) -> Result<Value, ShellError> {
+    Value::Error(ShellError::unexpected(
+        "Only numerical values are supported",
+    ))
+    .into()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::ShellError;
+    use super::SubCommand;
+
+    #[test]
+    fn examples_work_as_expected() -> Result<(), ShellError> {
+        use crate::examples::test as test_examples;
+
+        test_examples(SubCommand {})
+    }
+}

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

@@ -0,0 +1,3 @@
+pub mod abs;
+
+pub use abs::SubCommand as MathAbs;