From c484a6216e4640b75798fc63e8bee13bf57f1b06 Mon Sep 17 00:00:00 2001
From: Andre Wagner <WagnerAndre@JohnDeere.com>
Date: Thu, 30 Apr 2026 15:19:40 -0500
Subject: [PATCH] .

---
 CMakeLists.txt                 |  1 +
 src/assembler/as_exceptions.hh | 17 +++++++++++++++++
 src/assembler/lexer.cc         | 32 +++++++++++++++++++++++++++++---
 src/assembler/lexer.hh         | 10 +++++++---
 4 files changed, 54 insertions(+), 6 deletions(-)
 create mode 100644 src/assembler/as_exceptions.hh

diff --git a/CMakeLists.txt b/CMakeLists.txt
index ba78482..429baa6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -84,6 +84,7 @@ add_library(lib${PROJECT_NAME} SHARED
         src/assembler/lexer.hh
         src/assembler/assembler.cc
         src/assembler/assembler.hh
+        src/assembler/as_exceptions.hh
 )
 
 target_compile_options(lib${PROJECT_NAME} PRIVATE ${warnings})
diff --git a/src/assembler/as_exceptions.hh b/src/assembler/as_exceptions.hh
new file mode 100644
index 0000000..0690bbd
--- /dev/null
+++ b/src/assembler/as_exceptions.hh
@@ -0,0 +1,17 @@
+#ifndef TYCHE_VM_EXCEPTIONS_HH
+#define TYCHE_VM_EXCEPTIONS_HH
+
+#include <stdexcept>
+#include <string>
+
+namespace tyche::as {
+
+class AssemblyError : public std::runtime_error
+{
+public:
+    explicit AssemblyError(std::string const& str) : std::runtime_error(str.c_str()) {}
+};
+
+}
+
+#endif //TYCHE_VM_EXCEPTIONS_HH
diff --git a/src/assembler/lexer.cc b/src/assembler/lexer.cc
index 2a9c5ab..4ecf7c8 100644
--- a/src/assembler/lexer.cc
+++ b/src/assembler/lexer.cc
@@ -1,20 +1,46 @@
 #include "lexer.hh"
 
+#include "as_exceptions.hh"
+
 namespace tyche::as {
 
 void Lexer::reset()
 {
-
+    pos_ = 0;
+    ingest_next_token();
 }
 
 Token Lexer::peek() const
 {
-    return {};
+    return look_ahead_;
 }
 
 Token Lexer::ingest()
 {
-    return {};
+    Token t = look_ahead_;
+    ingest_next_token();
+    return t;
+}
+
+void Lexer::ingest_next_token()
+{
+    char c = source_.at(pos_);
+
+    if (pos_ >= source_.size()) {
+        look_ahead_ = { TokenType::EOF_, "" };
+    } else if (c == '.') {
+
+    } else if (c == '"') {
+
+    } else if (isdigit(c)) {
+
+    } else if (isalpha(c)) {
+
+    } else if (c == '\n') {
+
+    } else if (c != ' ' && c != '\t' && c != '\r') {
+        throw AssemblyError(std::string("Unexpected character '") + c + "' (ascii: " + std::to_string((int) c) + ")");
+    }
 }
 
 } // tyche
diff --git a/src/assembler/lexer.hh b/src/assembler/lexer.hh
index 1fc4fbd..f5584d7 100644
--- a/src/assembler/lexer.hh
+++ b/src/assembler/lexer.hh
@@ -6,7 +6,7 @@
 
 namespace tyche::as {
 
-enum class TokenType { Directive, Instruction, Number, Float, String, Enter, EOF_ };
+enum class TokenType { BOF, Directive, Instruction, Number, Float, String, Enter, EOF_ };
 
 struct Token {
     TokenType   type;
@@ -15,14 +15,18 @@ struct Token {
 
 class Lexer {
 public:
-    explicit Lexer(std::string source) : source_(std::move(source)) {}
+    explicit Lexer(std::string source) : source_(std::move(source) + "\n") { reset(); }
 
     void reset();
     [[nodiscard]] Token peek() const;
     [[nodiscard]] Token ingest();
 
 private:
-    std::string source_;
+    const std::string source_;
+    size_t pos_ = 0;
+    Token look_ahead_;
+
+    void ingest_next_token();
 };
 
 } // tyche