Make a calc command (#1280)

Cargo.lock

@@ -1927,6 +1927,16 @@ dependencies = [
  "rustc_version",
 ]
 
+[[package]]
+name = "meval"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f79496a5651c8d57cd033c5add8ca7ee4e3d5f7587a4777484640d9cb60392d9"
+dependencies = [
+ "fnv",
+ "nom 1.2.4",
+]
+
 [[package]]
 name = "mime"
 version = "0.3.14"
@@ -2070,6 +2080,12 @@ version = "0.1.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "72ef4a56884ca558e5ddb05a1d1e7e1bfd9a68d9ed024c21704cc98872dae1bb"
 
+[[package]]
+name = "nom"
+version = "1.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a5b8c256fd9471521bcb84c3cdba98921497f1a331cbc15b8030fc63b82050ce"
+
 [[package]]
 name = "nom"
 version = "4.2.3"
@@ -2170,6 +2186,7 @@ dependencies = [
  "itertools 0.8.2",
  "language-reporting",
  "log",
+ "meval",
  "natural",
  "nom 5.1.0",
  "nom-tracable",

Cargo.toml

@@ -123,6 +123,7 @@ termcolor = "1.1.0"
 natural = "0.3.0"
 parking_lot = "0.10.0"
 futures-timer = "1.0.2"
+meval = "0.2"
 
 clipboard = {version = "0.5", optional = true }
 ptree = {version = "0.2" }

src/cli.rs

@@ -268,6 +268,7 @@ pub async fn cli() -> Result<(), Box<dyn Error>> {
             whole_stream_command(Save),
             per_item_command(Cpy),
             whole_stream_command(Date),
+            per_item_command(Calc),
             per_item_command(Mkdir),
             per_item_command(Move),
             whole_stream_command(Version),

src/commands.rs

@@ -7,6 +7,7 @@ mod to_delimited_data;
 pub(crate) mod append;
 pub(crate) mod args;
 pub(crate) mod autoview;
+pub(crate) mod calc;
 pub(crate) mod cd;
 pub(crate) mod classified;
 pub(crate) mod clip;
@@ -107,6 +108,7 @@ pub(crate) use command::{
 };
 
 pub(crate) use append::Append;
+pub(crate) use calc::Calc;
 pub(crate) use compact::Compact;
 pub(crate) use config::Config;
 pub(crate) use count::Count;

src/commands/calc.rs

@@ -0,0 +1,57 @@
+use crate::commands::PerItemCommand;
+use crate::prelude::*;
+use nu_errors::ShellError;
+use nu_protocol::{CallInfo, Primitive, ReturnSuccess, UntaggedValue, Value};
+
+pub struct Calc;
+
+impl PerItemCommand for Calc {
+    fn name(&self) -> &str {
+        "calc"
+    }
+
+    fn usage(&self) -> &str {
+        "Parse a math expression into a number"
+    }
+
+    fn run(
+        &self,
+        _call_info: &CallInfo,
+        _registry: &CommandRegistry,
+        raw_args: &RawCommandArgs,
+        input: Value,
+    ) -> Result<OutputStream, ShellError> {
+        calc(input, raw_args)
+    }
+}
+
+fn calc(input: Value, args: &RawCommandArgs) -> Result<OutputStream, ShellError> {
+    let name_span = &args.call_info.name_tag.span;
+
+    let output = if let Ok(string) = input.as_string() {
+        match parse(&string, &input.tag) {
+            Ok(value) => ReturnSuccess::value(value),
+            Err(err) => Err(ShellError::labeled_error(
+                "Calulation error",
+                err,
+                &input.tag.span,
+            )),
+        }
+    } else {
+        Err(ShellError::labeled_error(
+            "Expected a string from pipeline",
+            "requires string input",
+            name_span,
+        ))
+    };
+
+    Ok(vec![output].into())
+}
+
+pub fn parse(math_expression: &str, tag: impl Into<Tag>) -> Result<Value, String> {
+    let num = meval::eval_str(math_expression);
+    match num {
+        Ok(num) => Ok(UntaggedValue::from(Primitive::from(num)).into_value(tag)),
+        Err(error) => Err(error.to_string()),
+    }
+}

tests/commands/calc.rs

@@ -0,0 +1,49 @@
+use nu_test_support::{nu, pipeline};
+
+#[test]
+fn calculates_two_plus_two() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        echo "2 + 2" | calc
+        "#
+    ));
+
+    assert!(actual.contains("4.0"));
+}
+
+#[test]
+fn calculates_two_to_the_power_six() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        echo "2 ^ 6" | calc
+        "#
+    ));
+
+    assert!(actual.contains("64.0"));
+}
+
+#[test]
+fn calculates_three_multiplied_by_five() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        echo "3 * 5" | calc
+        "#
+    ));
+
+    assert!(actual.contains("15.0"));
+}
+
+#[test]
+fn calculates_twenty_four_divided_by_two() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        echo "24 / 2" | calc
+        "#
+    ));
+
+    assert!(actual.contains("12.0"));
+}

tests/commands/mod.rs

@@ -1,4 +1,5 @@
 mod append;
+mod calc;
 mod cd;
 mod compact;
 mod cp;