feat: evaluate string literals

internal/ast/ast.go

@@ -11,6 +11,7 @@ var _ Node = (*Program)(nil)
 var _ Expression = (*IdentifierExpression)(nil)
 var _ Expression = (*IntegerExpression)(nil)
 var _ Expression = (*BooleanExpression)(nil)
+var _ Expression = (*StringExpression)(nil)
 var _ Expression = (*IfExpression)(nil)
 var _ Expression = (*FuncExpression)(nil)
 var _ Expression = (*CallExpression)(nil)

internal/evaluator/evaluator.go

@@ -53,6 +53,8 @@ func (e *evaluator) Eval(node ast.Node) (object.Object, error) {
 		return object.NewInteger(node.Value), nil
 	case *ast.BooleanExpression:
 		return booleanConv(node.Value), nil
+	case *ast.StringExpression:
+		return object.NewString(node.Value), nil
 	case *ast.IfExpression:
 		return e.evalIfExpression(node)
 	case *ast.FuncExpression:

internal/evaluator/evaluator_test.go

@@ -558,6 +558,25 @@ var _ = Describe("Evaluator", func() {
 			})
 		})
 
+		Context("string object", func() {
+			It("string expression", func() {
+				text = `
+				"hello world";
+				`
+				expectedObject := object.NewString("hello world")
+				expectedErrors := []error{}
+
+				// parse the program
+				program, errs = p.ParseProgram(text)
+				Expect(errs).To(Equal(expectedErrors))
+
+				// evaluate the AST tree
+				obj, err := e.Eval(program)
+				Expect(err).To(BeNil())
+				Expect(obj).To(Equal(expectedObject))
+			})
+		})
+
 		Context("if conditionals", func() {
 			It("if condition is truthy", func() {
 				text = `

internal/object/object.go

@@ -10,6 +10,7 @@ import (
 // interface compliance check
 var _ Object = (*Integer)(nil)
 var _ Object = (*Boolean)(nil)
+var _ Object = (*String)(nil)
 var _ Object = (*Nil)(nil)
 var _ Object = (*ReturnValue)(nil)
 var _ Object = (*Error)(nil)
@@ -20,6 +21,7 @@ type ObjectType string
 var (
 	INTEGER_OBJ      = ObjectType("INTEGER")
 	BOOLEAN_OBJ      = ObjectType("BOOLEAN")
+	STRING_OBJ       = ObjectType("STRING")
 	NIL_OBJ          = ObjectType("NIL")
 	RETURN_VALUE_OBJ = ObjectType("RETURN_VALUE")
 	ERROR_OBJ        = ObjectType("ERROR")
@@ -84,6 +86,28 @@ func (b *Boolean) IsTruthy() bool {
 	return b.Value
 }
 
+type String struct {
+	Value string
+}
+
+func NewString(value string) *String {
+	return &String{
+		Value: value,
+	}
+}
+
+func (s *String) Type() ObjectType {
+	return STRING_OBJ
+}
+
+func (s *String) Inspect() string {
+	return s.Value
+}
+
+func (s *String) IsTruthy() bool {
+	return len(s.Value) > 0
+}
+
 // Nil represents the absence of any value
 type Nil struct{}
 

internal/object/object_test.go

@@ -66,7 +66,7 @@ var _ = Describe("Object", func() {
 		})
 	})
 
-	Describe("Boolean", func() {
+	Describe("Nil", func() {
 		It("false nil object", func() {
 			expectedNilObj := object.NIL
 			obj := object.NewNil()
@@ -77,4 +77,34 @@ var _ = Describe("Object", func() {
 			Expect(obj.IsTruthy()).To(Equal(false))
 		})
 	})
+
+	Describe("String", func() {
+		It("false string object", func() {
+			var val string = ""
+
+			expectedStringObj := &object.String{
+				Value: val,
+			}
+			obj := object.NewString(val)
+
+			Expect(obj).To(Equal(expectedStringObj))
+			Expect(obj.Inspect()).To(Equal(""))
+			Expect(obj.Type()).To(Equal(object.STRING_OBJ))
+			Expect(obj.IsTruthy()).To(Equal(false))
+		})
+
+		It("truthy string object", func() {
+			var val string = "hello"
+
+			expectedStringObj := &object.String{
+				Value: val,
+			}
+			obj := object.NewString(val)
+
+			Expect(obj).To(Equal(expectedStringObj))
+			Expect(obj.Inspect()).To(Equal("hello"))
+			Expect(obj.Type()).To(Equal(object.STRING_OBJ))
+			Expect(obj.IsTruthy()).To(Equal(true))
+		})
+	})
 })