From 145d61ba57bad9b2160eaa2e168ff1d232d778e7 Mon Sep 17 00:00:00 2001
From: tijani <tijani@tijanilawal.com>
Date: Thu, 26 May 2022 19:23:01 +0000
Subject: [PATCH] - The parser can now check for errors. - The test now handles
 checking for errors.

git-svn-id: https://svn.tlawal.org/svn/monkey@19 f6afcba9-9ef1-4bdd-9b72-7484f5705bac
---
 parser/parser.go      | 33 +++++++++++++++++++++++----------
 parser/parser_test.go | 16 ++++++++++++++++
 2 files changed, 39 insertions(+), 10 deletions(-)

diff --git a/parser/parser.go b/parser/parser.go
index a5cce03..63f8fea 100644
--- a/parser/parser.go
+++ b/parser/parser.go
@@ -1,6 +1,7 @@
 package parser
 
 import (
+	"fmt"
 	"monkey/ast"
 	"monkey/lexer"
 	"monkey/token"
@@ -10,10 +11,12 @@ type Parser struct {
 	lexer         *lexer.Lexer
 	current_token token.Token
 	peek_token    token.Token
+
+	errors []string
 }
 
 func New(l_lexer *lexer.Lexer) *Parser {
-	l_parser := &Parser{lexer: l_lexer}
+	l_parser := &Parser{lexer: l_lexer, errors: []string{}}
 
 	// Read two tokens so current_token and peek_token are both set
 	l_parser.next_token()
@@ -22,6 +25,10 @@ func New(l_lexer *lexer.Lexer) *Parser {
 	return l_parser
 }
 
+func (l_parser *Parser) Errors() []string {
+	return l_parser.errors
+}
+
 func (l_parser *Parser) ParseProgram() *ast.Program {
 	program := &ast.Program{}
 	program.Statements = []ast.Statement{}
@@ -68,6 +75,21 @@ func (l_parser *Parser) parse_let_statement() *ast.LetStatement {
 	return statement
 }
 
+func (l_parser *Parser) expect_peek(l_token token.TokenType) bool {
+	if l_parser.peek_token_is(l_token) {
+		l_parser.next_token()
+		return true
+	} else {
+		l_parser.peek_error(l_token)
+		return false
+	}
+}
+
+func (l_parser *Parser) peek_error(l_token token.TokenType) {
+	message := fmt.Sprintf("expected next token to be %s, got %s", l_token, l_parser.peek_token.Type)
+	l_parser.errors = append(l_parser.errors, message)
+}
+
 func (l_parser *Parser) current_token_is(l_token token.TokenType) bool {
 	return l_parser.current_token.Type == l_token
 }
@@ -75,12 +97,3 @@ func (l_parser *Parser) current_token_is(l_token token.TokenType) bool {
 func (l_parser *Parser) peek_token_is(l_token token.TokenType) bool {
 	return l_parser.peek_token.Type == l_token
 }
-
-func (l_parser *Parser) expect_peek(l_token token.TokenType) bool {
-	if l_parser.peek_token_is(l_token) {
-		l_parser.next_token()
-		return true
-	} else {
-		return false
-	}
-}
diff --git a/parser/parser_test.go b/parser/parser_test.go
index aa7fd03..5cbc3de 100644
--- a/parser/parser_test.go
+++ b/parser/parser_test.go
@@ -17,6 +17,8 @@ func TestLetStatement(l_test *testing.T) {
 	l_parser := New(l_lexer)
 
 	program := l_parser.ParseProgram()
+	check_parser_errors(l_test, l_parser)
+
 	if program == nil {
 		l_test.Fatalf("ParseProgram() returned nil")
 	}
@@ -65,3 +67,17 @@ func testLetStatement(l_test *testing.T, statement ast.Statement, name string) b
 	}
 	return true
 }
+
+func check_parser_errors(l_test *testing.T, l_parser *Parser) {
+	errors := l_parser.Errors()
+	if len(errors) == 0 {
+		return
+	}
+
+	l_test.Errorf("parser has %d errors", len(errors))
+	
+	for _, message := range errors {
+		l_test.Errorf("parser error: %q", message)
+	}
+	l_test.FailNow()
+}