feat: parse string expression

internal/ast/ast.go

@@ -161,6 +161,31 @@ func NewBooleanExpression(value bool) *BooleanExpression {
 	}
 }
 
+// StringExpression implements the Expression interface
+type StringExpression struct {
+	// the string token
+	Token token.Token
+	Value string
+}
+
+func (se *StringExpression) expressionNode() {}
+
+func (se *StringExpression) TokenLiteral() string {
+	return se.Token.Literal
+}
+
+func (se *StringExpression) String() string {
+	return se.Token.Literal
+}
+
+// NewStringExpression creates a String node
+func NewStringExpression(literal string) *StringExpression {
+	return &StringExpression{
+		Token: token.New(token.STRING, literal),
+		Value: literal,
+	}
+}
+
 // IfExpression implements the Expression interface
 type IfExpression struct {
 	// the if token

internal/parser/parser.go

@@ -51,6 +51,8 @@ func New(l lexer.Lexer) Parser {
 	// handler for boolean expression
 	p.registerPrefixParseFn(token.TRUE, p.parseBoolean)
 	p.registerPrefixParseFn(token.FALSE, p.parseBoolean)
+	// handler for string expression
+	p.registerPrefixParseFn(token.STRING, p.parseString)
 	// handler for grouped expression
 	p.registerPrefixParseFn(token.LPAREN, p.parseGroupedExpression)
 	// handler for if expression
@@ -276,6 +278,10 @@ func (p *parser) parseBoolean() (ast.Expression, error) {
 	return ast.NewBooleanExpression(value), nil
 }
 
+func (p *parser) parseString() (ast.Expression, error) {
+	return ast.NewStringExpression(p.curToken.Literal), nil
+}
+
 func (p *parser) parseGroupedExpression() (ast.Expression, error) {
 	// move forward to make p.curToken point to the first token after the ( token
 	p.nextToken()

internal/parser/parser_test.go

@@ -82,6 +82,24 @@ var _ = Describe("Parser", func() {
 				Expect(errs).To(Equal(expectedErrors))
 			})
 
+			It("string expressions", func() {
+				text = `
+				"foo";
+				"foo bar";
+				`
+				expectedProgram := &ast.Program{
+					Statements: []ast.Statement{
+						ast.NewExpressionStatement(ast.NewStringExpression("foo")),
+						ast.NewExpressionStatement(ast.NewStringExpression("foo bar")),
+					},
+				}
+				expectedErrors := []error{}
+
+				program, errs = p.ParseProgram(text)
+				Expect(program).To(Equal(expectedProgram))
+				Expect(errs).To(Equal(expectedErrors))
+			})
+
 			It("if expressions", func() {
 				text = `
 				if (x < y) { x; };