fix array bug with string concat in display

core/src/interp.rs

@@ -2366,6 +2366,23 @@ impl Interpreter {
             (Op::Add, Value::Number(a), Value::Str(b)) => Ok(Value::Str(format!("{}{}", format_number(*a), b))),
             (Op::Add, Value::Str(a), Value::Bool(b)) => Ok(Value::Str(format!("{}{}", a, b))),
             (Op::Add, Value::Bool(a), Value::Str(b)) => Ok(Value::Str(format!("{}{}", a, b))),
+            (Op::Add, Value::Str(s), other) => Ok(Value::Str(format!("{}{}", s, other.display()))),
+            (Op::Add, other, Value::Str(s)) => Ok(Value::Str(format!("{}{}", other.display(), s))),
+            (Op::Add, Value::Array(a), Value::Array(b)) => {
+                let mut out = a.clone();
+                out.extend(b.iter().cloned());
+                Ok(Value::Array(out))
+            }
+            (Op::Add, Value::Array(a), other) => {
+                let mut out = a.clone();
+                out.push(other.clone());
+                Ok(Value::Array(out))
+            }
+            (Op::Add, other, Value::Array(a)) => {
+                let mut out = vec![other.clone()];
+                out.extend(a.iter().cloned());
+                Ok(Value::Array(out))
+            }
 
             (Op::Lt, Value::Number(a), Value::Number(b)) => Ok(Value::Bool(a < b)),
             (Op::Gt, Value::Number(a), Value::Number(b)) => Ok(Value::Bool(a > b)),
@@ -6164,6 +6181,56 @@ fn find(arr, target) {
         assert!(matches!(v, Value::Number(n) if n == 3.0));
     }
 
+    #[test]
+    fn add_str_plus_array_stringifies() {
+        let mut i = Interpreter::new();
+        let v = i.eval_expr_str(r#""Diff: " + [1, 2]"#).unwrap();
+        match v {
+            Value::Str(s) => assert_eq!(s, "Diff: [1, 2]"),
+            _ => panic!("expected Str, got {:?}", v),
+        }
+    }
+
+    #[test]
+    fn add_array_plus_str_stringifies() {
+        let mut i = Interpreter::new();
+        let v = i.eval_expr_str(r#"[1, 2] + " items""#).unwrap();
+        match v {
+            Value::Str(s) => assert_eq!(s, "[1, 2] items"),
+            _ => panic!(),
+        }
+    }
+
+    #[test]
+    fn add_array_plus_array_concats() {
+        let mut i = Interpreter::new();
+        let v = i.eval_expr_str("[1, 2] + [3, 4]").unwrap();
+        match v {
+            Value::Array(a) => assert_eq!(a.len(), 4),
+            _ => panic!(),
+        }
+    }
+
+    #[test]
+    fn add_array_plus_number_appends() {
+        let mut i = Interpreter::new();
+        let v = i.eval_expr_str("[1, 2] + 3").unwrap();
+        match v {
+            Value::Array(a) => assert_eq!(a.len(), 3),
+            _ => panic!(),
+        }
+    }
+
+    #[test]
+    fn add_chains_str_array_str() {
+        let mut i = Interpreter::new();
+        let v = i.eval_expr_str(r#""Diff: " + [10, 20] + " + Sum: " + [30, 40]"#).unwrap();
+        match v {
+            Value::Str(s) => assert_eq!(s, "Diff: [10, 20] + Sum: [30, 40]"),
+            _ => panic!(),
+        }
+    }
+
     #[test]
     fn rand_unit_range() {
         let mut i = Interpreter::new();