feat: adding String concatenation

Author: DeveloperC286

src/evaluator/expression/infix/mod.rs

@@ -82,6 +82,13 @@ impl Evaluator {
                         true => Ok(Object::True),
                         false => Ok(Object::False),
                     },
+                    Token::Plus => {
+                        let mut concatenated = left_value;
+                        concatenated.push_str(&right_value);
+                        Ok(Object::String {
+                            value: concatenated,
+                        })
+                    }
                     _ => Err(EvaluationError::UnknownOperator),
                 },
                 _ => Err(EvaluationError::TypeMismatch),

src/evaluator/expression/infix/tests/mod.rs

@@ -70,6 +70,15 @@ fn test_evaluator_infix_boolean_expressions(code: &str, snapshot_name: &str) {
     assert_expected_returned_object!(code, snapshot_name);
 }
 
+#[rstest(
+    code,
+    snapshot_name,
+    case("\"123\" + \"456\"", "test_evaluator_infix_string_expressions_case1")
+)]
+fn test_evaluator_infix_string_expressions(code: &str, snapshot_name: &str) {
+    assert_expected_returned_object!(code, snapshot_name);
+}
+
 #[rstest(
     code,
     snapshot_name,

src/evaluator/expression/infix/tests/snapshots/monkey_interpreter__evaluator__expression__infix__tests__test_evaluator_infix_string_expressions_case1.snap

@@ -0,0 +1,10 @@
+---
+source: src/evaluator/expression/infix/tests/mod.rs
+expression: "evaluator.evaluate(crate::syntax_analysis::SyntaxAnalysis::from(crate::lexical_analysis::LexicalAnalysis::from(code).unwrap()).unwrap())"
+
+---
+Ok(
+    String {
+        value: "123456",
+    },
+)