Fix #7: Code readthrough, comments

include/cons_expr/cons_expr.hpp

@@ -358,7 +358,7 @@ template<typename CharType> [[nodiscard]] constexpr Token<CharType> next_token(s
     auto location = std::next(input.begin());
     while (location != input.end()) {
       if (*location == chars::ch('\\')) {
-        in_escape = true;
+        in_escape = !in_escape;
       } else if (*location == chars::ch('"') && !in_escape) {
         ++location;
         break;

test/string_escape_tests.cpp

@@ -93,6 +93,41 @@ TEST_CASE("String escape edge cases", "[string][escape][edge]")
   STATIC_CHECK(evaluate_expected<std::string_view>("\"\\n\"", "\n"));
 }
 
+// Regression tests for issue #7: escaped backslash before the closing quote
+// caused the tokenizer to stay in escape mode and eat the terminator.
+TEST_CASE("Tokenizer backslash escape state", "[string][escape][tokenizer][regression][issue-7]")
+{
+  // Direct tokenizer test: `"a\\" "b"` must split into two string tokens.
+  // With the bug, `\\` left the tokenizer in escape mode, so the first `"`
+  // after `\\` was consumed instead of terminating the literal.
+  constexpr auto split_two_literals = []() constexpr {
+    auto token = lefticus::next_token(std::string_view(R"("a\\" "b")"));
+    return token.parsed == std::string_view(R"("a\\")")
+           && token.remaining == std::string_view(R"("b")");
+  };
+  STATIC_CHECK(split_two_literals());
+
+  // End-to-end: evaluating the two-literal sequence should yield "b".
+  STATIC_CHECK(evaluate_expected<std::string_view>(R"("a\\" "b")", "b"));
+
+  // `"\\"` is a valid one-character string whose content is a single backslash.
+  STATIC_CHECK(evaluate_expected<std::string_view>(R"("\\")", "\\"));
+
+  // A valid string ending in `\\` followed by a newline must parse cleanly
+  // and unescape to `a\`. With the bug the tokenizer ran past the terminator,
+  // leaving a token that did not end in `"`, so the parser reported the
+  // literal as unterminated.
+  STATIC_CHECK(evaluate_expected<std::string_view>("\"a\\\\\"\n", "a\\"));
+
+  // A consecutive-escape terminator: `"\\\\"` is two backslashes in the
+  // source string literal. Every pair must cancel so the final `"` closes.
+  constexpr auto double_escaped_backslash_pair = []() constexpr {
+    auto token = lefticus::next_token(std::string_view(R"("\\\\")"));
+    return token.parsed == std::string_view(R"("\\\\")") && token.remaining.empty();
+  };
+  STATIC_CHECK(double_escaped_backslash_pair());
+}
+
 // Branch Coverage Enhancement Tests - Missing String Cases
 
 TEST_CASE("String escape error conditions for coverage", "[string][escape][coverage]")