Improve expr parse (#3584)

* Require '-' to be a number for math

* Add test

* improve parse logic, add test

crates/nu-parser/src/parse.rs

@@ -1577,7 +1577,7 @@ fn parse_internal_command(
             let arg = {
                 let (new_idx, expr, err) = parse_positional_argument(
                     idx,
-                    &lite_cmd,
+                    lite_cmd,
                     &signature.positional[current_positional].0,
                     signature.positional.len() - current_positional - 1,
                     scope,
@@ -1802,7 +1802,14 @@ fn parse_call(
     } else if lite_cmd.parts[0].item.starts_with('$')
         || lite_cmd.parts[0].item.starts_with('\"')
         || lite_cmd.parts[0].item.starts_with('\'')
-        || lite_cmd.parts[0].item.starts_with('-')
+        || (lite_cmd.parts[0].item.starts_with('-')
+            && parse_arg(SyntaxShape::Number, scope, &lite_cmd.parts[0])
+                .1
+                .is_none())
+        || (lite_cmd.parts[0].item.starts_with('-')
+            && parse_arg(SyntaxShape::Range, scope, &lite_cmd.parts[0])
+                .1
+                .is_none())
         || lite_cmd.parts[0].item.starts_with('0')
         || lite_cmd.parts[0].item.starts_with('1')
         || lite_cmd.parts[0].item.starts_with('2')

tests/shell/pipeline/commands/internal.rs

@@ -618,6 +618,29 @@ fn index_out_of_bounds() {
     assert!(actual.err.contains("unknown row"));
 }
 
+#[test]
+fn dash_def() {
+    let actual = nu!(
+        cwd: ".",
+        r#"
+            def - [x, y] { $x - $y }; - 4 1
+        "#
+    );
+
+    assert_eq!(actual.out, "3");
+}
+
+#[test]
+fn negative_decimal_start() {
+    let actual = nu!(
+        cwd: ".",
+        r#"
+            -1.3 + 4
+        "#
+    );
+
+    assert_eq!(actual.out, "2.7");
+}
 #[test]
 fn index_row() {
     let actual = nu!(