feat: add parseIntegerLiteral

ast/ast.go

@@ -27,6 +27,7 @@ type Program struct {
 	Statements []Statement // A program is a list of statements
 }
 
+// TokenLiteral return the token literal of the first statement on ast
 func (p *Program) TokenLiteral() string {
 	if len(p.Statements) > 0 {
 		return p.Statements[0].TokenLiteral()
@@ -111,3 +112,12 @@ type Identifier struct {
 func (i *Identifier) expressionNode()      {}
 func (i *Identifier) TokenLiteral() string { return i.Token.Literal }
 func (i *Identifier) String() string       { return i.Value }
+
+type IntegerLiteral struct {
+	Token token.Token // the token.INT token
+	Value int64
+}
+
+func (il *IntegerLiteral) expressionNode()      {}
+func (il *IntegerLiteral) TokenLiteral() string { return il.Token.Literal }
+func (il *IntegerLiteral) String() string       { return il.Token.Literal }

parser/parser.go

@@ -5,6 +5,7 @@ import (
 	"monkey/ast"
 	"monkey/lexer"
 	"monkey/token"
+	"strconv"
 )
 
 type Parser struct {
@@ -28,6 +29,7 @@ func New(l *lexer.Lexer) *Parser {
 
 	p.prefixParseFns = make(map[token.TokenType]prefixParseFn)
 	p.registerPrefix(token.IDENT, p.parseIdentifier)
+	p.registerPrefix(token.INT, p.parseIntegerLiteral)
 
 	// Read two tokens, so curToken and peekToken are both set
 	p.nextToken()
@@ -116,6 +118,18 @@ func (p *Parser) parseReturnStatement() *ast.ReturnStatement {
 	return stmt
 }
 
+func (p *Parser) parseIntegerLiteral() ast.Expression {
+	lit := &ast.IntegerLiteral{Token: p.curToken}
+	value, err := strconv.ParseInt(p.curToken.Literal, 0, 64)
+	if err != nil {
+		msg := fmt.Sprintf("could not parse %q as integer", p.curToken.Literal)
+		p.errors = append(p.errors, msg)
+		return nil
+	}
+	lit.Value = value
+	return lit
+}
+
 func (p *Parser) parseExpressionStatement() *ast.ExpressionStatement {
 	stmt := &ast.ExpressionStatement{Token: p.curToken}
 

parser/parser_test.go

@@ -123,6 +123,34 @@ func TestIdentifierExpression(t *testing.T) {
 	}
 }
 
+func TestIntegerLiteralExpression(t *testing.T) {
+	input := "5;"
+	l := lexer.New(input)
+	p := New(l)
+	program := p.ParseProgram()
+	checkParserErrors(t, p)
+	if len(program.Statements) != 1 {
+		t.Fatalf("program has not enough statements. got=%d",
+			len(program.Statements))
+	}
+	stmt, ok := program.Statements[0].(*ast.ExpressionStatement)
+	if !ok {
+		t.Fatalf("program.Statements[0] is not ast.ExpressionStatement. got=%T",
+			program.Statements[0])
+	}
+	literal, ok := stmt.Expression.(*ast.IntegerLiteral)
+	if !ok {
+		t.Fatalf("exp not *ast.IntegerLiteral. got=%T", stmt.Expression)
+	}
+	if literal.Value != 5 {
+		t.Errorf("literal.Value not %d. got=%d", 5, literal.Value)
+	}
+	if literal.TokenLiteral() != "5" {
+		t.Errorf("literal.TokenLiteral not %s. got=%s", "5",
+			literal.TokenLiteral())
+	}
+}
+
 func checkParserErrors(t *testing.T, p *Parser) {
 	errors := p.Errors()
 	if len(errors) == 0 {