3 files changed, 104 insertions, 25 deletions

diff --git a/server/lexer/CMakeLists.txt b/server/lexer/CMakeLists.txt
index b62e47a..b5b8b63 100644
--- a/server/lexer/CMakeLists.txt
+++ b/server/lexer/CMakeLists.txt
@@ -1,2 +1,5 @@
+find_package(Boost REQUIRED COMPONENTS regex)
+
 add_library(lexer details/parse.cpp lexer.cpp token.cpp token_type.cpp)
 target_link_libraries(lexer PUBLIC common)
+target_link_libraries(lexer PRIVATE Boost::regex)
diff --git a/server/lexer/details/parse.cpp b/server/lexer/details/parse.cpp
index 464dfb2..01ef11c 100644
--- a/server/lexer/details/parse.cpp
+++ b/server/lexer/details/parse.cpp
@@ -6,9 +6,12 @@
 #include "../error.hpp"
 #include "../token_type.hpp"
 
+#include <boost/regex.hpp>
+
 #include <cstddef>
 
 #include <exception>
+#include <functional>
 #include <optional>
 #include <regex>
 #include <string>
@@ -17,45 +20,77 @@
 namespace math::server::lexer::details {
 namespace {
 
-std::string_view match_number(const std::string_view& input) {
-    static constexpr std::regex::flag_type flags =
-        std::regex_constants::ECMAScript |
-        std::regex_constants::icase;
-    // This is a hacky attempt to describe a C-like grammar for floating-point
-    // numbers using a regex (the tests seem to pass though).
-    // A proper NFA would be better, I guess.
-    static const std::regex number_regex{R"REGEX(^(?:\d+(?:\.\d*)?|\.\d+)(e[+-]?(\d*))?)REGEX", flags};
-
+std::cmatch std_regex_search(const std::string_view& input, const std::regex& regex) {
     std::cmatch match;
     {
         const auto begin = input.data();
         const auto end = begin + input.length();
-        if (!std::regex_search(begin, end, match, number_regex)) {
-            return {};
-        }
+        std::regex_search(begin, end, match, regex);
     }
+    return match;
+}
+
+boost::cmatch boost_regex_search(const std::string_view& input, const boost::regex& regex) {
+    boost::cmatch match;
     {
-        // If we have the numeric part of a number followed by 'e' and no digits,
-        // 1) that 'e' definitely belongs to this number token,
-        // 2) the user forgot to type in the required digits.
-        const auto& exponent = match[1];
-        const auto& abs_power = match[2];
-        if (exponent.matched && abs_power.matched && abs_power.length() == 0) {
-            throw LexerError{"exponent has no digits: " + match[0].str()};
-        }
+        const auto begin = input.data();
+        const auto end = begin + input.length();
+        boost::regex_search(begin, end, match, regex);
+    }
+    return match;
+}
+
+// CMatch is either std::cmatch or boost::cmatch.
+template <typename CMatch>
+void check_exponent(const CMatch& match) {
+    // If we have the numeric part of a number followed by 'e' and no digits,
+    // 1) that 'e' definitely belongs to this number token,
+    // 2) the user forgot to type in the required digits.
+    const auto& exponent = match[1];
+    const auto& abs_power = match[2];
+    if (exponent.matched && abs_power.matched && abs_power.length() == 0) {
+        throw LexerError{"exponent has no digits: " + match[0].str()};
     }
+}
+
+// This is a hacky attempt to describe a C-like grammar for floating-point
+// numbers using a regex (the tests seem to pass though).
+// A proper NFA would be better, I guess.
+const std::string_view NUMBER_REGEX = R"REGEX(^(?:\d+(?:\.\d*)?|\.\d+)(e[+-]?(\d*))?)REGEX";
+
+std::string_view std_match_number(const std::string_view& input) {
+    static constexpr auto flags =
+        std::regex_constants::ECMAScript |
+        std::regex_constants::icase;
+    static const std::regex number_regex{NUMBER_REGEX.data(), NUMBER_REGEX.length(), flags};
+
+    const auto match = std_regex_search(input, number_regex);
+    if (match.empty()) {
+        return {};
+    }
+    check_exponent(match);
     return {match[0].first, static_cast<std::size_t>(match[0].length())};
 }
 
-bool starts_with(const std::string_view& a, const std::string_view& b) noexcept {
-    return a.length() >= b.length()
-        && a.compare(0, b.length(), b) == 0;
+std::string_view boost_match_number(const std::string_view& input) {
+    static const boost::regex number_regex{NUMBER_REGEX.data(), NUMBER_REGEX.length(), boost::regex::icase};
+
+    const auto match = boost_regex_search(input, number_regex);
+    if (match.empty()) {
+        return {};
+    }
+    check_exponent(match);
+    return {match[0].first, static_cast<std::size_t>(match[0].length())};
 }
 
+std::string_view match_number(const std::string_view& input) {
+    return std_match_number(input);
 }
 
-std::optional<double> parse_number(const std::string_view& input, std::string_view& token) {
-    const auto view = match_number(input);
+using NumberMatcher = std::function<std::string_view (const std::string_view&)>;
+
+std::optional<double> parse_number(const std::string_view& input, const NumberMatcher& match, std::string_view& token) {
+    const auto view = match(input);
     if (!view.data()) {
         return {};
     }
@@ -69,6 +104,39 @@ std::optional<double> parse_number(const std::string_view& input, std::string_vi
     return {};
 }
 
+bool starts_with(const std::string_view& a, const std::string_view& b) noexcept {
+    return a.length() >= b.length()
+        && a.compare(0, b.length(), b) == 0;
+}
+
+}
+
+namespace impl {
+
+std::optional<double> std_parse_number(const std::string_view& input, std::string_view& token) {
+    return parse_number(input, &std_match_number, token);
+}
+
+std::optional<double> std_parse_number(const std::string_view& input) {
+    std::string_view token;
+    return std_parse_number(input, token);
+}
+
+std::optional<double> boost_parse_number(const std::string_view& input, std::string_view& token) {
+    return parse_number(input, &boost_match_number, token);
+}
+
+std::optional<double> boost_parse_number(const std::string_view& input) {
+    std::string_view token;
+    return boost_parse_number(input, token);
+}
+
+}
+
+std::optional<double> parse_number(const std::string_view& input, std::string_view& token) {
+    return impl::std_parse_number(input, token);
+}
+
 std::optional<double> parse_number(const std::string_view& input) {
     std::string_view token;
     return parse_number(input, token);
diff --git a/server/lexer/details/parse.hpp b/server/lexer/details/parse.hpp
index 72da234..6a8688b 100644
--- a/server/lexer/details/parse.hpp
+++ b/server/lexer/details/parse.hpp
@@ -11,6 +11,14 @@
 #include <string_view>
 
 namespace math::server::lexer::details {
+namespace impl {
+
+std::optional<double> std_parse_number(const std::string_view&, std::string_view&);
+std::optional<double> std_parse_number(const std::string_view&);
+std::optional<double> boost_parse_number(const std::string_view&, std::string_view&);
+std::optional<double> boost_parse_number(const std::string_view&);
+
+}
 
 // Exposed for testing:
 std::string_view parse_whitespace(const std::string_view&);