4.4 Arrays (evaluating array literals)

Author: cedrickchee

evaluator/evaluator.go

@@ -125,6 +125,13 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 
 		// Call the function. Apply the function to the arguments.
 		return applyFunction(function, args)
+
+	case *ast.ArrayLiteral:
+		elements := evalExpressions(node.Elements, env)
+		if len(elements) == 1 && isError(elements[0]) {
+			return elements[0]
+		}
+		return &object.Array{Elements: elements}
 	}
 
 	return nil

evaluator/evaluator_test.go

@@ -402,6 +402,25 @@ func TestBuiltinFunctions(t *testing.T) {
 	}
 }
 
+func TestArrayLiterals(t *testing.T) {
+	input := "[1, 2 * 2, 3 + 3]"
+
+	evaluated := testEval(input)
+	result, ok := evaluated.(*object.Array)
+	if !ok {
+		t.Fatalf("object is not Array. got=%T (%+v)", evaluated, evaluated)
+	}
+
+	if len(result.Elements) != 3 {
+		t.Fatalf("array has wrong num of elements. got=%d",
+			len(result.Elements))
+	}
+
+	testIntegerObject(t, result.Elements[0], 1)
+	testIntegerObject(t, result.Elements[1], 4)
+	testIntegerObject(t, result.Elements[2], 6)
+}
+
 func testEval(input string) object.Object {
 	l := lexer.New(input)
 	p := parser.New(l)

object/object.go

@@ -36,6 +36,9 @@ const (
 
 	// BUILTIN_OBJ is the Builtin object type.
 	BUILTIN_OBJ = "BUILTIN"
+
+	// ARRAY_OBJECT is the Array object type.
+	ARRAY_OBJ = "ARRAY"
 )
 
 // BuiltinFunction represents the builtin function type.
@@ -175,3 +178,27 @@ func (b *Builtin) Type() ObjectType { return BUILTIN_OBJ }
 
 // Inspect returns a stringified version of the object for debugging.
 func (b *Builtin) Inspect() string { return "builtin function" }
+
+// Array is the array literal type that holds a slice of Object(s).
+type Array struct {
+	Elements []Object
+}
+
+// Type returns the type of the object
+func (ao *Array) Type() ObjectType { return ARRAY_OBJ }
+
+// Inspect returns a stringified version of the object for debugging.
+func (ao *Array) Inspect() string {
+	var out bytes.Buffer
+
+	elements := []string{}
+	for _, e := range ao.Elements {
+		elements = append(elements, e.Inspect())
+	}
+
+	out.WriteString("[")
+	out.WriteString(strings.Join(elements, ", "))
+	out.WriteString("]")
+
+	return out.String()
+}