From 65f4ce27861a919002f2446ee43a6bf111760aef Mon Sep 17 00:00:00 2001
From: Alexander Luzgarev <mahalex@gmail.com>
Date: Sat, 31 Mar 2018 22:31:29 +0200
Subject: [PATCH] Lex string literals with escaped quotes

---
 Lexer.Tests/MLexerShould.cs | 10 ++++++++++
 Lexer/MLexer.cs             | 21 ++++++++++++++++++---
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/Lexer.Tests/MLexerShould.cs b/Lexer.Tests/MLexerShould.cs
index 28fd34e..a75bbe3 100644
--- a/Lexer.Tests/MLexerShould.cs
+++ b/Lexer.Tests/MLexerShould.cs
@@ -215,5 +215,15 @@ namespace Parser.Tests
             Assert.AreEqual(TokenKind.StringLiteral, tokens[0].Kind);
             Assert.AreEqual("just a string", tokens[0].PureToken.Value);
         }
+
+        [Test]
+        public void ParseStringLiteralWithEscapedQuotes()
+        {
+            var sut = CreateLexer("'just a ''string'''");
+            var tokens = sut.ParseAll();
+            Assert.AreEqual(2, tokens.Count);
+            Assert.AreEqual(TokenKind.StringLiteral, tokens[0].Kind);
+            Assert.AreEqual("just a 'string'", tokens[0].PureToken.Value);
+        }
     }
 }
\ No newline at end of file
diff --git a/Lexer/MLexer.cs b/Lexer/MLexer.cs
index 93af021..d9d4d80 100644
--- a/Lexer/MLexer.cs
+++ b/Lexer/MLexer.cs
@@ -306,11 +306,24 @@ namespace Lexer
         private PureToken ContinueParsingStringLiteral()
         {
             Window.ConsumeChar();
+            var pieces = new List<string>();
             var n = 0;
             while (true) {
                 if (Window.PeekChar(n) == '\'')
                 {
-                    break;
+                    if (Window.PeekChar(n + 1) == '\'')
+                    {
+                        var piece = Window.GetAndConsumeChars(n);
+                        pieces.Add(piece);
+                        Window.ConsumeChar();
+                        Window.ConsumeChar();
+                        pieces.Add("'");
+                        n = -1;
+                    }
+                    else
+                    {
+                        break;
+                    }
                 }
                 if (IsEolOrEof(Window.PeekChar(n)))
                 {
@@ -319,9 +332,11 @@ namespace Lexer
                 n++;
             }
 
-            var literal = Window.GetAndConsumeChars(n);
+            var lastPiece = Window.GetAndConsumeChars(n);
+            pieces.Add(lastPiece);
+            var total = string.Join("", pieces);
             Window.ConsumeChar();
-            return PureTokenFactory.CreateStringLiteral(literal);
+            return PureTokenFactory.CreateStringLiteral(total);
         }
 
         private PureToken ContinueParsingDoubleQuotedStringLiteral()