Introduced helper in Interpreter to reduce duplication, and fortifi…

…ed supporting unit test.
quephird · Mar 23, 2024 · 2c69877 · 2c69877
1 parent 2e7ddca
commit 2c69877
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Showing 2 changed files with 25 additions and 16 deletions.
diff --git a/slox/Interpreter.swift b/slox/Interpreter.swift
@@ -387,13 +387,8 @@ class Interpreter {
         if case .instance(let leftList as LoxList) = leftValue,
            case .instance(let rightList as LoxList) = rightValue,
            case .plus = oper.type {
-            guard case .instance(let listClass as LoxClass) = try environment.getValue(name: "List") else {
-                fatalError()
-            }
-
             let newElements = leftList.elements + rightList.elements
-            let list = LoxList(elements: newElements, klass: listClass)
-            return .instance(list)
+            return try makeList(elements: newElements)
         }
 
         switch oper.type {
@@ -530,13 +525,7 @@ class Interpreter {
             return try evaluate(expr: element)
         }
 
-        guard case .instance(let listClass as LoxClass) = try environment.getValue(name: "List") else {
-            // TODO: Do we need throw an exception here?
-            fatalError()
-        }
-
-        let list = LoxList(elements: elementValues, klass: listClass)
-        return .instance(list)
+        return try makeList(elements: elementValues)
     }
 
     private func handleSubscriptGetExpression(listExpr: ResolvedExpression,
@@ -568,4 +557,13 @@ class Interpreter {
         list[Int(index)] = value
         return value
     }
+
+    private func makeList(elements: [LoxValue]) throws -> LoxValue {
+        guard case .instance(let listClass as LoxClass) = try environment.getValue(name: "List") else {
+            fatalError()
+        }
+
+        let list = LoxList(elements: elements, klass: listClass)
+        return .instance(list)
+    }
 }
diff --git a/sloxTests/InterpreterTests.swift b/sloxTests/InterpreterTests.swift
@@ -482,12 +482,23 @@ quux.count
     func testInterpretAddingTwoLists() throws {
         let input = """
 var xyzzy = [1, 2, 3] + [4, 5, 6];
-xyzzy.count
+xyzzy
 """
 
         let interpreter = Interpreter()
-        let actual = try interpreter.interpretRepl(source: input)
-        let expected: LoxValue = .number(6)
+        guard case .instance(let list as LoxList) = try interpreter.interpretRepl(source: input) else {
+            XCTFail()
+            return
+        }
+        let actual = list.elements
+        let expected: [LoxValue] = [
+            .number(1),
+            .number(2),
+            .number(3),
+            .number(4),
+            .number(5),
+            .number(6),
+        ]
         XCTAssertEqual(actual, expected)
     }