Support compound statements

source/lexer.cpp

@@ -58,6 +58,12 @@ namespace elna::source
         return *this;
     }
 
+    text_iterator text_iterator::operator+(std::size_t step)
+    {
+        auto result = *this;
+        return ++result;
+    }
+
     bool text_iterator::operator==(const text_iterator& that) const noexcept
     {
         return this->m_buffer == that.m_buffer;
@@ -309,6 +315,11 @@ namespace elna::source
 
                 tokens.emplace_back(token::type::factor_operator, _operator.c_str(), iterator.position());
             }
+            else if (*iterator == ':' && iterator + 1 != text_end && *(iterator + 1) == '=')
+            {
+                tokens.emplace_back(token::type::assignment, iterator.position());
+                ++iterator;
+            }
             else
             {
                 return source_result(unexpected_character{ std::string{ *iterator }, iterator.position() });