feat(furc): introduce while loop statement

Refs: #2

furc/src/front/lexer.cpp

@@ -1,5 +1,7 @@
 #include "furc/front/lexer.hpp"
 
+#include "furc/front/token.hpp"
+
 #include <cctype>
 #include <limits>
 #include <map>
@@ -97,6 +99,7 @@ token_r lexer::next_token() {
                 { "return", keyword_token::Return },
                 { "if", keyword_token::If },
                 { "else", keyword_token::Else },
+                { "while", keyword_token::While },
             };
 
             if (auto it = s_keywords.find(value); it != s_keywords.end()) return { location, it->second };
@@ -185,4 +188,4 @@ location lexer::current_location() {
     return { m_filename, m_row, m_cursor - m_lineStart };
 }
 
-} // namespace furc::front
+} // namespace furc::front