diff --git a/SLS_C/include/sls/lexer.h b/SLS_C/include/sls/lexer.h
index e24080b..afc20da 100644
--- a/SLS_C/include/sls/lexer.h
+++ b/SLS_C/include/sls/lexer.h
@@ -8,6 +8,16 @@
 
 #include <stdint.h>
 
+#include "sls_errors.h"
+
+typedef struct {
+    const char *filename;
+    const char *source_code;
+    size_t pos;
+    size_t column;
+    size_t line;
+} LexerInfo;
+
 typedef enum {
     TOKEN_EOF,
     TOKEN_IDENTIFIER,
@@ -91,9 +101,25 @@ typedef struct {
     };
 } Token;
 
-typedef struct TokenStream {
-    Token token;
-    struct TokenStream *next;
-} TokenStream;
+typedef struct LexerTokenResult {
+    SlsResultType type;
+    union {
+        Token result;
+        SlsError error;
+    };
+    struct LexerTokenResult *next;
+} LexerTokenResult;
+
+typedef struct {
+    SlsResultType type;
+    union {
+        LexerTokenResult *result;
+        SlsError error;
+    };
+} LexerResult;
+
+void init_lexer(LexerInfo *lexer_info, const char *filename, const char *source_code);
+LexerResult lexical_analysis(LexerInfo *lexer_info);
+void clean_token_result(LexerTokenResult* head);
 
 #endif // SLS_LEXER_H
diff --git a/SLS_C/include/sls/sls_errors.h b/SLS_C/include/sls/sls_errors.h
new file mode 100644
index 0000000..6e0a330
--- /dev/null
+++ b/SLS_C/include/sls/sls_errors.h
@@ -0,0 +1,19 @@
+// Kyler Olsen
+// YREA SLS
+// SLS Error Header
+// October 2025
+
+#ifndef SLS_ERROR_H
+#define SLS_ERROR_H
+
+typedef struct {
+    const char *message;
+    int code;
+} SlsError;
+
+typedef enum {
+    SLS_ERROR,
+    SLS_RESULT,
+} SlsResultType;
+
+#endif // SLS_ERROR_H