...

3 files changed, 20 insertions, 4 deletions

diff --git a/include/cru/common/String.hpp b/include/cru/common/String.hpp
index 8197c402..42143c9d 100644
--- a/include/cru/common/String.hpp
+++ b/include/cru/common/String.hpp
@@ -1,8 +1,8 @@
 #pragma once
 #include "Base.hpp"
 
-#include "StringUtil.hpp"
 #include "Range.hpp"
+#include "StringUtil.hpp"
 
 #include <cstdint>
 #include <iterator>
@@ -119,15 +119,28 @@ class CRU_BASE_API String {
   iterator insert(const_iterator pos, std::uint16_t value) {
     return this->insert(pos, &value, 1);
   }
-  iterator insert(const_iterator pos, std::uint16_t* str, Index size);
+  iterator insert(const_iterator pos, const std::uint16_t* str, Index size);
   iterator erase(const_iterator pos) { return this->erase(pos, pos + 1); }
   iterator erase(const_iterator start, const_iterator end);
   void push_back(std::uint16_t value) { this->append(value); }
   void pop_back() { this->erase(cend() - 1); }
   void append(std::uint16_t value) { this->insert(cend(), value); }
-  void append(std::uint16_t* str, Index size) {
+  void append(const std::uint16_t* str, Index size) {
     this->insert(cend(), str, size);
   }
+  void append(const String& other) { append(other.data(), other.size()); }
+
+ public:
+  String& operator+=(const String& other) {
+    append(other);
+    return *this;
+  }
+
+  String operator+(const String& other) const {
+    String result(*this);
+    result += other;
+    return result;
+  }
 
  public:
   Utf16CodePointIterator CodePointIterator() const {
diff --git a/include/cru/parse/Grammar.hpp b/include/cru/parse/Grammar.hpp
index 5b37ceba..659c4302 100644
--- a/include/cru/parse/Grammar.hpp
+++ b/include/cru/parse/Grammar.hpp
@@ -46,6 +46,9 @@ class Grammar : public Object {
   // Require grammar has no cycles or empty-productions.
   void EliminateLeftRecursions();
 
+  // Algorithm 4.21
+  void LeftFactor();
+
  private:
   Nonterminal* start_symbol_;
   std::vector<Terminal*> terminals_;
diff --git a/src/parse/Grammar.cpp b/src/parse/Grammar.cpp
index 3bd387d7..95c65e99 100644
--- a/src/parse/Grammar.cpp
+++ b/src/parse/Grammar.cpp
@@ -148,7 +148,7 @@ void Grammar::EliminateLeftRecursions() {
             auto new_right = right;
             new_right.insert(new_right.cbegin(), jp->GetRight().cbegin(),
                              jp->GetRight().cend());
-            CreateProduction(String{}, ni, std::move(new_right));
+            CreateProduction(u"", ni, std::move(new_right));
           }
         }
       }