lexer can now read single character tokens

src/lexer/lexer.cpp

@@ -0,0 +1,34 @@
+#include "lexer.hpp"
+
+#include "token/token.hpp"
+
+#include <iostream>
+
+namespace lexer {
+    token::token lexer::next_token() {
+        char c;
+        if (!(input >> c))
+            return {token::type::END_OF_FILE, ""};
+
+        switch (c) {
+        case '=':
+            return {token::type::ASSIGN, c};
+        case '+':
+            return {token::type::PLUS, c};
+        case ',':
+            return {token::type::COMMA, c};
+        case ';':
+            return {token::type::SEMICOLON, c};
+        case '(':
+            return {token::type::LPAREN, c};
+        case ')':
+            return {token::type::RPAREN, c};
+        case '{':
+            return {token::type::LBRACE, c};
+        case '}':
+            return {token::type::RBRACE, c};
+        }
+        return {token::type::ILLEGAL, c};
+    };
+
+} // namespace lexer

src/lexer/lexer.hpp

@@ -1,7 +1,10 @@
 #include "token/token.hpp"
 
+#include <istream>
+
 namespace lexer {
     struct lexer {
+        std::istream& input;
         token::token next_token();
     };
 } // namespace lexer

src/token/token.hpp

@@ -8,5 +8,9 @@ namespace token {
     struct token {
         ::token::type type;
         std::string literal;
+
+        token(::token::type t, std::string s): type(t), literal(s) {}
+
+        token(::token::type t, char c): type(t), literal(1, c) {}
     };
 } // namespace token

test/lexer.cpp

@@ -3,6 +3,7 @@
 #include "token/type.hpp"
 
 #include <doctest.h>
+#include <sstream>
 #include <string>
 
 TEST_CASE("next token") {
@@ -12,8 +13,9 @@ TEST_CASE("next token") {
     };
 
     std::string input = "=+(){},;";
+    std::istringstream ss(input);
 
-    lexer::lexer l{};
+    lexer::lexer l{ss};
 
     test tests[] = {
         {token::type::ASSIGN, "="},