diff --git a/assembler/assembler/__init__.py b/assembler/assembler/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/assembler/assembler/assembler.py b/assembler/assembler/assembler.py
new file mode 100644
index 0000000..53f556c
--- /dev/null
+++ b/assembler/assembler/assembler.py
@@ -0,0 +1,280 @@
+from collections import deque
+
+from .context import FileContext
+from .tokenize import Tokenizer, WHITESPACE
+from .opcodes import make_opcodes
+from .util import can_be_mark, can_convert_to_int, autoint
+from .directives import SetDirective
+
+class ParsingError(Exception): 
+	pass
+
+class Assembler(object):
+	"""
+	This class is used for generating bytecode from a file containing assembly.
+
+	Also required is the memory definition of the interpreter given as a dict::
+
+		{
+			"registers": <register_count>,
+			"memory": <number of memory words>,
+			"program_memory": <number of words available for the program>
+		}
+
+	And the definition of the commands. This is a list of dicts::
+		
+		[
+			{
+				"mnemonic": <mnemonic>,
+				"args": [
+						("register"|"memory"|"program_memory"|"direct_input"), ...
+					]
+			}
+		]
+	
+	The method ``parse`` will parse the input file and ``bindump`` will dump the binary
+	bytecode into a file.
+	"""
+	def __init__(self, file_, memory_definition, command_definition, custom_directives):
+		self._file_context = FileContext(file_)
+		self._code_objects = deque()
+		self._memory_definition = memory_definition
+		self._command_definition = command_definition
+		self._word_count = 0
+		self._marks = {}
+
+		self._opcodes = make_opcodes([cmd["mnemonic"] for cmd in command_definition])
+		self._commands_by_mnemonic = {cmd["mnemonic"]: cmd for cmd in command_definition}
+		self._tokenizer = Tokenizer(self._file_context)
+
+		self._directives = {"set": SetDirective()}
+		self._directives.update(custom_directives)
+
+	def parse(self):
+		try:
+			for token in self._tokenizer:
+
+				# Comments
+				if(token == ";"):
+					while(token != "\n"):
+						token = next(self._tokenizer)
+					continue
+
+				# Commands
+				if(token in self._commands_by_mnemonic):
+					self.parse_command(token)
+					continue
+
+				# Directives
+				if(token == "."):
+					self.parse_directive()
+					continue
+
+				# The default is trying to parse a mark
+				if(not can_be_mark(token)):
+					self.raise_unexpected_token(token
+						, "comment, command, directive or mark"
+						, token)
+				self.parse_mark(token)
+		except StopIteration:
+			raise ParsingError("Unexpected EOF while parsing.")
+			
+		for mark, mark_data in self._marks.items():
+			if(mark_data["target"] < 0):
+				raise ParsingError("Mark {} undefined. Referenced in lines: {}".format(
+						mark
+						, mark_data["references"]))
+
+		self._code_objects = [self._marks[c]["target"] if c in self._marks else c 
+							for c in self._code_objects ]
+
+	def bindump(self, file_):
+		# FIXME:
+		# Make this work for tons of data.
+		# Or is that necessary?
+		return file_.write(bytes(self._code_objects))
+
+
+	def parse_mark(self, token):
+		should_be_colon = next(self._tokenizer)
+
+		if(should_be_colon != ":"):
+			self.raise_unexpected_token(token, "':'", should_be_colon)
+
+		should_be_newline = next(self._tokenizer)
+		if(should_be_newline != "\n"):
+			self.raise_unexpected_token(token + ":", "'\\n'", should_be_newline)
+
+		if(token in self._marks):
+			if(self._marks[token]["target"] != -1):
+				raise ParsingError("Error in line {} column {} mark already defined: '{}'. Previous was in line {}.".format(
+						self._line
+						, self._column
+						, token
+						, self._marks[token]["target_line"]))
+			self._marks[token]["target"] = self._word_count
+			self._marks[token]["target_line"] = self._line
+
+		else:
+			self._marks[token] = {
+				"target": self._word_count
+				, "target_line": self._line
+				, "references": []
+			}
+
+		should_be_newline = next(self._tokenizer)
+		if(should_be_newline != "\n"):
+			self.raise_unexpected_token(token, "newline", should_be_newline)
+
+
+	def parse_directive(self):
+		should_be_name = next(self._tokenizer)
+		
+		if(not should_be_name in self._directives):
+			self.raise_unexpected_token(".", "directive name", should_be_name)
+
+		words = self._directives[should_be_name].parse(self, self._tokenizer)
+		
+		self._word_count += len(words)
+		self._code_objects.extend(words)
+
+		should_be_newline = next(self._tokenizer)
+		if(should_be_newline != "\n"):
+			self.raise_unexpected_token(".", "newline", should_be_newline)
+
+
+
+
+	def parse_command(self, cmd):
+
+		self._code_objects.append(self._opcodes[cmd])
+		self._word_count += 1
+
+		if(not self._commands_by_mnemonic[cmd]["args"]):
+			token = next(self._tokenizer)
+			if(token != "\n"):
+				self.raise_unexpected_token(cmd, "newline", token)
+			return 
+
+		should_be_whitespace = next(self._tokenizer)
+		if(should_be_whitespace not in WHITESPACE 
+				or should_be_whitespace == "\n"):
+			self.raise_unexpected_token(cmd, "' '", should_be_whitespace)
+
+		should_be_an_argument = next(self._tokenizer)
+		argument = self.check_and_convert_argument(cmd
+				, should_be_an_argument
+				, self._commands_by_mnemonic[cmd]["args"][0])
+		self._word_count += 1
+		self._code_objects.append(argument)
+		
+
+		for argument in self._commands_by_mnemonic[cmd]["args"][1:]:
+			should_be_comma = next(self._tokenizer)
+			if(should_be_comma != ","):
+				self.raise_unexpected_token(cmd, should_be_whitespace)
+
+			self._word_count += 1
+			self._code_objects.append(
+					self.check_and_convert_argument(
+						cmd
+						, next(self._tokenizer)
+						, argument))
+
+		should_be_newline = next(self._tokenizer)
+		if(should_be_newline != "\n"):
+			self.raise_unexpected_token(cmd, "newline", should_be_newline)
+			
+			
+	def raise_unexpected_token(self, after, expected, got):
+		raise ParsingError("Error in line {} column {} after '{}': expected {}, got '{}'".format(
+					self._file_context._line
+					, self._file_context._column
+					, after
+					, expected
+					, got))
+
+	def raise_invalid_address(self, after, memtype, maxval, got):
+		raise ParsingError("Error in line {} column {} after '{}': value {} is invalid for {} (max is {})".format(
+					self._file_context._line
+					, self._file_context._column
+					, after
+					, got
+					, memtype
+					, maxval))
+
+	def check_and_convert_argument(self, cmd, argument, argument_definition):
+		if(argument_definition == "register"):
+			if(not argument.startswith("r")):
+				self.raise_unexpected_token(cmd, "register name", argument)
+			register_offset = argument[1:]
+			raise_could_not_convert_register_offset = False
+			try:
+				register_offset = int(register_offset)
+			except:
+				raise_could_not_convert_register_offset = True
+
+			if(raise_could_not_convert_register_offset):
+				self.raise_unexpected_token(cmd, "register name", argument)
+
+			if(register_offset > self._memory_definition["registers"] 
+					or register_offset < 0):
+				self.raise_invalid_address(cmd
+						, "register"
+						, self._memory_definition["registers"]
+						, register_offset)
+
+			return register_offset
+
+		if(argument_definition == "memory"):
+			if(not can_convert_to_int(argument)):
+				self.raise_unexpected_token(cmd, "integer address", argument)
+			argument = autoint(argument)
+
+			if(argument < 0 or argument > self._memory_definition["memory"]):
+				self.raise_invalid_address(cmd
+						, "memory"
+						, self._memory_definition["memory"]
+						, argument)
+			return argument
+
+		if(argument_definition == "program_memory"):
+			if(not can_convert_to_int(argument)):
+				if(not can_be_mark(argument)):
+					self.raise_unexpected_token(cmd, "integer address or mark", argument)
+				if(argument in self._marks):
+					self._marks[argument]["references"].append(self._line)
+					if(self._marks[argument]["target"] != -1):
+						return self._marks[argument]["target"]
+					return argument
+				self._marks[argument] = {
+					"target": -1
+					, "target_line": 0
+					, "references": [self._line]
+				}
+				return argument
+
+
+			argument = autoint(argument)
+
+			if(argument < 0 or argument > self._memory_definition["program_memory"]):
+				self.raise_invalid_address(cmd
+						, "program_memory"
+						, self._memory_definition["program_memory"]
+						, argument)
+			return argument
+
+
+		if(can_convert_to_int(argument)):
+			return autoint(argument)
+
+		if(not can_be_mark(argument)):
+			self.raise_unexpected_token(cmd, "integer, char or mark", argument)
+		if(argument in self._marks and self._marks[argument] >= 0):
+			return self._marks[argument]
+		self._marks[argument] = -1
+		return argument
+
+
+			
+
diff --git a/assembler/assembler/context.py b/assembler/assembler/context.py
new file mode 100644
index 0000000..3863a00
--- /dev/null
+++ b/assembler/assembler/context.py
@@ -0,0 +1,28 @@
+from collections import deque
+
+class FileContext(object):
+	def __init__(self, file_):
+		self._file = file_
+		self._line = 0
+		self._column = 0
+		self._column_stack = deque()
+
+	def getc(self):
+		c = self._file.read(1)
+		if(c == "\n"):
+			self._line += 1
+			self._column_stack.append(self._column)
+			self._column = 0
+		else:
+			self._column += 1
+
+		return c
+
+	def ungetc(self, c):
+		self._file.seek(self._file.tell() - 1, 0)
+		if(c == "\n"):
+			self._line -= 1
+			self._column = self._column_stack.pop()
+		else:
+			self._column -= 1
+
diff --git a/assembler/assembler/directives.py b/assembler/assembler/directives.py
new file mode 100644
index 0000000..24b6c99
--- /dev/null
+++ b/assembler/assembler/directives.py
@@ -0,0 +1,42 @@
+"""
+Directives for explicitly modifying the program memory.
+"""
+
+from abc import ABC, abstractmethod
+from collections import deque
+
+class AbstractDirective(ABC):
+	@abstractmethod
+	def parse(self, assembler, tokenizer):
+		"""
+		Parse the directive by converting the text to a list of words.
+		Returns a list of 16bit words.
+		"""
+		pass
+
+
+
+class SetDirective(AbstractDirective):
+	def parse(self, assembler, tokenizer):
+		words = deque()
+		should_be_bracket = next(tokenizer)
+		if(not should_be_bracket == "["):
+			assembler.raise_unexpected_token(".set", "'['", should_be_bracket)
+
+		while(True):
+			should_be_value = next(tokenizer)
+			if(not can_convert_to_int(should_be_value)):
+				assembler.raise_unexpected_token(".set"
+						, "integer or character value"
+						, should_be_value)
+			words.append(autoint(should_be_value))
+
+			comma_or_bracket = next(tokenizer)
+			if(not comma_or_bracket in (",", "]")):
+				assembler.raise_unexpected_token(".set"
+						, "',' or ']'"
+						, comma_or_bracket)
+
+			if(comma_or_bracket == "]"):
+				break
+		return list(words)
diff --git a/assembler/assembler/opcodes.py b/assembler/assembler/opcodes.py
new file mode 100644
index 0000000..15c9ba3
--- /dev/null
+++ b/assembler/assembler/opcodes.py
@@ -0,0 +1,33 @@
+
+
+class Autoinserter(object):
+	def __init__(self):
+		self.mayor = 2
+		self.minor = 1
+	def __next__(self):
+		"""Generate the next opcode"""
+		# 10bit opcode
+		opcode = 0b1111111111
+
+		# Calculate this opcode.
+		opcode *= self.minor
+		opcode //= self.mayor
+
+		# The lower 6 bits are reserved.
+		opcode <<= 6
+		# 16 bits in total. Should not matter.
+		opcode &= 0xffff 
+
+		# Update the state.
+		self.minor = (self.minor + 2) % self.mayor
+		if(self.minor == 1):
+			self.mayor *= 2
+
+		return opcode
+	def __iter__(self):
+		return self
+
+def make_opcodes(mnemonics_in_order):
+
+	ai = Autoinserter()
+	return {mnemonic: opcode for (mnemonic, opcode) in zip(mnemonics_in_order, ai)}
diff --git a/assembler/assembler/tokenize.py b/assembler/assembler/tokenize.py
new file mode 100644
index 0000000..71be23f
--- /dev/null
+++ b/assembler/assembler/tokenize.py
@@ -0,0 +1,55 @@
+from collections import deque
+
+WHITESPACE = {" ", "\t", "\n", "\r"}
+TOKENS_END_OF_WORD = WHITESPACE | {";", ":", ",", ".", "[", "]"}
+
+TOKENS_EXPECT_NEWLINE = {":", "]"}
+
+
+class Tokenizer(object):
+	def __init__(self, context):
+		self._context = context
+		self._expect_newline = False
+		self._expect_whitespace = False
+
+	def __iter__(self):
+		return self
+	def __next__(self):
+		"""
+		Return the next token.
+		"""
+
+		current_token = deque()
+
+		while(True):
+			c = self._context.getc()
+
+			# Sometimes we need the explicit newline.
+			if(self._expect_newline and c == "\n"):
+				self._expect_newline = False
+				return c
+
+			# Skip multiple whitespaces.
+			if(c in WHITESPACE and not current_token):
+				if(self._expect_whitespace):
+					self._expect_whitespace = False
+					return c
+				continue
+
+			if(c in TOKENS_END_OF_WORD):
+				if(current_token):
+					self._context.ungetc(c)
+					if(c in WHITESPACE):
+						self._expect_whitespace = True
+					return "".join(current_token)
+				else:
+					if(c in TOKENS_EXPECT_NEWLINE):
+						self._expect_newline = True
+					return c
+
+			if(not c):
+				raise StopIteration()
+
+			current_token.append(c)
+
+
diff --git a/assembler/assembler/util.py b/assembler/assembler/util.py
new file mode 100644
index 0000000..60d043b
--- /dev/null
+++ b/assembler/assembler/util.py
@@ -0,0 +1,85 @@
+"""
+Utility functions used for parsing.
+"""
+
+
+def can_be_mark(argument):
+	"""
+	The ``argument`` can be interpreted as a Mark.
+	"""
+	a = ord("a")
+	a_z = [chr(a + i) for i in range(26)]
+	A = ord("A")
+	A_Z = [chr(A + i) for i in range(26)]
+	null = ord("0")
+	null_9 = [chr(null + i) for i in range(10)]
+
+	if(not argument[0] in a_z):
+		return False
+
+	for char in argument[1:]:
+		if(not (char in a_z
+			or char in A_Z
+			or char in null_9
+			or char == "_")):
+			return False
+	return True
+
+	
+
+def can_convert_to_int(value):
+	"""
+	``value`` can be converted to an integer.
+
+	**Note** that this returns ``True`` if the value is a 
+	character definition like ``'a'``.
+	"""
+	if(value.startswith("0x")):
+		try:
+			int(value[2:], 16)
+			return True
+		except:
+			return False
+
+	if(value.startswith("0b")):
+		try:
+			int(value[2:], 2)
+			return True
+		except:
+			return False
+
+	if(value.startswith("'") and value.endswith("'")):
+		if(len(value) == 3):
+			return True
+		if(len(value) == 4):
+			if(value[1:-1] in {"\\n", "\\r", "\\t"}):
+				return True
+		return False
+
+	try:
+		int(value)
+		return True
+	except:
+		return False
+
+def autoint(value):
+	"""
+	Convert ``value`` to an integer automatically.
+	"""
+	escape_sequences = {"\\n": "\n", "\\r": "\r", "\\t":"\t"}
+	if(value.startswith("0x")):
+		return int(value[2:], 16)
+
+	if(value.startswith("0b")):
+		return int(value[2:], 2)
+
+	if(value.startswith("'") and value.endswith("'")):
+		if(len(value) == 3):
+			return ord(value[1:-1])
+		if(len(value) == 4):
+			if(value[1:-1] in escape_sequences):
+				return ord(escape_sequences[value[1:-1]])
+
+	return int(value)
+	
+