diff --git a/main.py b/main.py
new file mode 100755
index 0000000..0772f44
--- /dev/null
+++ b/main.py
@@ -0,0 +1,104 @@
+from parser import Parser
+import tokens
+
+
+class lambda_runner:
+	def __init__(self):
+		self.macro_table = {}
+		self.expr = None
+
+	# Apply a list of definitions
+	def run_names(self, lines):
+		print("Added names:")
+		for l in lines:
+			if isinstance(l, str):
+				e = Parser.parse_assign(l)
+			else:
+				e = l
+
+			if e.label in self.macro_table:
+				raise NameError(f"Label {e.label} exists!")
+
+			e.exp.bind_variables()
+			self.macro_table[e.label] = e.exp
+			print(f"\t{e}")
+		print("\n")
+
+	def set_expr(self, expr: str | None = None):
+		if expr == None:
+			self.expr = None
+			print("Removed expression.\n")
+			return
+
+		self.expr = Parser.parse_expression(expr)
+		self.expr.bind_variables()
+		print(f"Set expression to {self.expr}\n")
+
+	def run(self):
+		if isinstance(self.expr, tokens.lambda_apply):
+			self.expr = self.expr.expand(self.macro_table)
+		elif isinstance(self.expr, tokens.lambda_func):
+			self.expr = self.expr.expand(self.macro_table)
+		else:
+			return None
+		return self.expr
+
+
+r = lambda_runner()
+
+r.run_names([
+	"T = a -> b -> a",
+	"F = a -> b -> a",
+	"NOT = a -> (a F T)",
+	"AND = a -> b -> (a F b)",
+	"OR = a -> b -> (a T b)",
+	"XOR = a -> b -> (a (NOT a b) b)"
+])
+
+r.run_names([
+	"w = x -> (x x)",
+	"W = (w w)",
+	"Y = f -> ( (x -> (f (x x))) (x -> (f (x x))) )",
+	#"l = if_true -> if_false -> which -> ( which if_true if_false )"
+])
+
+r.run_names([
+	"inc = n -> f -> x -> (f (n f x))",
+	"zero = a -> x -> x",
+	"one = f -> x -> (f x)",
+])
+
+print("\n")
+
+#AND = r.run()
+#OR = r.run()
+#XOR = r.run()
+
+r.set_expr(
+	"(" +
+	"inc (inc (inc (zero)))"
+	+ ")"
+)
+
+print(repr(r.expr))
+print("")
+
+outs = [str(r.expr)]
+for i in range(300):
+	x = r.run()
+	s = str(x)
+	p = s if len(s) < 100 else s[:97] + "..."
+
+	if s in outs:
+		print(p)
+		print("\nLoop detected, exiting.")
+		break
+
+	if x is None:
+		print("\nCannot evaluate any further.")
+		break
+
+	outs.append(s)
+	print(p)
+
+print(f"Performed {i} {'operations' if i != 1 else 'operation'}.")
\ No newline at end of file
diff --git a/parser.py b/parser.py
new file mode 100755
index 0000000..2bba6b1
--- /dev/null
+++ b/parser.py
@@ -0,0 +1,65 @@
+import pyparsing as pp
+import tokens
+
+class Parser:
+	"""
+	Macro_def must be on its own line.
+	macro_def  :: var = expr
+
+	var        :: word
+	lambda_fun :: var -> expr
+	call       :: '(' (var | expr) ')' +
+	expr       :: define | var | call | '(' expr ')'
+	"""
+
+	lp = pp.Suppress("(")
+	rp = pp.Suppress(")")
+	func_char = pp.Suppress("->")
+	macro_char = pp.Suppress("=")
+
+	# Simple tokens
+	pp_expr = pp.Forward()
+	pp_name = pp.Word(pp.alphas + "_")
+	pp_name.set_parse_action(tokens.macro.from_parse)
+
+	# Function definitions.
+	# Right associative.
+	#
+	# <var> => <exp>
+	pp_lambda_fun = pp_name + func_char + pp_expr
+	pp_lambda_fun.set_parse_action(tokens.lambda_func.from_parse)
+
+	# Assignment.
+	# Can only be found at the start of a line.
+	#
+	# <var> = <exp>
+	pp_macro_def = pp.line_start() + pp_name + macro_char + pp_expr
+	pp_macro_def.set_parse_action(tokens.macro_expression.from_parse)
+
+	# Function calls.
+	# `tokens.lambda_func.from_parse` handles chained calls.
+	#
+	# <var>(<exp>)
+	# <var>(<exp>)(<exp>)(<exp>)
+	# (<exp>)(<exp>)
+	# (<exp>)(<exp>)(<exp>)(<exp>)
+	pp_call = pp.Forward()
+	pp_call <<= pp_expr[2, ...]
+	pp_call.set_parse_action(tokens.lambda_apply.from_parse)
+
+	pp_expr <<= pp_lambda_fun ^ (lp + pp_expr + rp) ^ pp_name ^ (lp + pp_call + rp)
+	pp_all = pp_expr | pp_macro_def
+
+	@staticmethod
+	def parse_expression(line):
+		return Parser.pp_expr.parse_string(line, parse_all = True)[0]
+
+	@staticmethod
+	def parse_assign(line):
+		return (
+			Parser.pp_macro_def
+		).parse_string(line, parse_all = True)[0]
+
+	@staticmethod
+	def run_tests(lines):
+		return Parser.pp_macro_def.run_tests(lines)
\ No newline at end of file
diff --git a/tokens.py b/tokens.py
new file mode 100755
index 0000000..0b3b2d1
--- /dev/null
+++ b/tokens.py
@@ -0,0 +1,420 @@
+from typing import Type
+
+
+class free_variable:
+	"""
+	Represents a free variable.
+
+	This object does not reduce to
+	anything, since it has no meaning.
+
+	Any name in an expression that isn't
+	a macro or a bound variable is assumed
+	to be a free variable.
+	"""
+
+	def __init__(self, label: str):
+		self.label = label
+
+	def __repr__(self):
+		return f"<freevar {self.label}>"
+
+	def __str__(self):
+		return f"{self.label}"
+
+
+class macro:
+	"""
+	Represents a "macro" in lambda calculus,
+	a variable that expands to an expression.
+
+	These don't have inherent logic, they
+	just make writing and reading expressions
+	easier.
+
+	These are defined as follows:
+	<macro name> = <expression>
+	"""
+
+	@staticmethod
+	def from_parse(result):
+		return macro(
+			result[0],
+		)
+
+	def __init__(self, name):
+		self.name = name
+	def __repr__(self):
+		return f"<{self.name}>"
+	def __str__(self):
+		return self.name
+
+	def __eq__(self, other):
+		if not isinstance(other, macro):
+			raise TypeError("Can only compare macro with macro")
+		return self.name == other.name
+
+	def expand(self, macro_table = {}, *, auto_free_vars = True):
+		if self.name in macro_table:
+			return macro_table[self.name]
+		elif not auto_free_vars:
+			raise NameError(f"Name {self.name} is not defined!")
+		else:
+			return free_variable(self.name)
+
+
+class macro_expression:
+	"""
+	Represents a line that looks like
+		<name> = <expression>
+
+	Doesn't do anything particularly interesting,
+	just holds an expression until it is stored
+	in the runner's macro table.
+	"""
+
+	@staticmethod
+	def from_parse(result):
+		return macro_expression(
+			result[0].name,
+			result[1]
+		)
+
+	def __init__(self, label, exp):
+		self.label = label
+		self.exp = exp
+
+	def __repr__(self):
+		return f"<{self.label} := {self.exp!r}>"
+
+	def __str__(self):
+		return f"{self.label} := {self.exp}"
+
+
+
+
+
+bound_variable_counter = 0
+class bound_variable:
+	def __init__(self, forced_id = None):
+		global bound_variable_counter
+
+		if forced_id is None:
+			self.identifier = bound_variable_counter
+			bound_variable_counter += 1
+		else:
+			self.identifier = forced_id
+
+	def __eq__(self, other):
+		if not isinstance(other, bound_variable):
+			raise TypeError(f"Cannot compare bound_variable with {type(other)}")
+		return self.identifier == other.identifier
+
+	def __repr__(self):
+		return f"<in {self.identifier}>"
+
+class lambda_func:
+	"""
+	Represents a function.
+		Defined like λa.aa
+
+	After being created by the parser, a function
+	needs to have its variables bound. This cannot
+	happen during parsing, since the parser creates
+	functions "inside-out," and we need all inner
+	functions before we bind variables.
+	"""
+
+	@staticmethod
+	def from_parse(result):
+		return lambda_func(
+			result[0],
+			result[1]
+		)
+
+	def __init__(self, input_var, output):
+		self.input = input_var
+		self.output = output
+
+	def __repr__(self) -> str:
+		return f"<{self.input!r} → {self.output!r}>"
+
+	def __str__(self) -> str:
+		return f"λ{self.input}.{self.output}"
+
+
+	def bind_variables(
+			self,
+			placeholder: macro | None = None,
+			val: bound_variable | None = None,
+			*,
+			binding_self: bool = False
+		) -> None:
+		"""
+		Go through this function and all the functions inside it,
+		and replace the strings generated by the parser with bound
+		variables or free variables.
+
+		If values are passed to `placeholder` and `val,`
+		we're binding the variable of a function containing
+		this one. If they are both none, start the binding
+		chain with this function.
+
+		If only one of those arguments is None, something is very wrong.
+
+		`placeholder` is a macro, NOT A STRING!
+		The parser assumes all names are macros at first, variable
+		binding fixes those that are actually bound variables.
+
+		If `binding_self` is True, don't throw an error on a name conflict
+		and don't bind this function's input variable.
+		This is used when we're calling this method to bind this function's
+		variable.
+		"""
+
+
+		if (placeholder is None) and (val != placeholder):
+			raise Exception(
+				"Error while binding variables: placeholder and val are both None."
+			)
+
+		# We only need to check for collisions if we're
+		# binding another function's variable. If this
+		# function starts the bind chain, skip that step.
+		if not ((placeholder is None) and (val is None)):
+			if not binding_self and isinstance(self.input, macro):
+				if self.input == placeholder:
+					raise NameError("Bound variable name conflict.")
+
+		# If this function's variables haven't been bound yet,
+		# bind them BEFORE binding the outer function's.
+		#
+		# If we bind inner functions' variables before outer
+		# functions' variables, we won't be able to detect
+		# name conflicts.
+		if isinstance(self.input, macro) and not binding_self:
+			new_bound_var = bound_variable()
+			self.bind_variables(
+				self.input,
+				new_bound_var,
+				binding_self = True
+			)
+			self.input = new_bound_var
+
+
+		# Bind variables inside this function.
+		if isinstance(self.output, macro):
+			if self.output == placeholder:
+				self.output = val
+		elif isinstance(self.output, lambda_func):
+			self.output.bind_variables(placeholder, val)
+		elif isinstance(self.output, lambda_apply):
+			self.output.bind_variables(placeholder, val)
+
+	# Expand this function's output.
+	# For functions, this isn't done unless
+	# its explicitly asked for.
+	def expand(self, macro_table = {}):
+		new_out = self.output
+		if isinstance(self.output, macro):
+			new_out = self.output.expand(macro_table)
+
+			# If the macro becomes a free variable, expand again.
+			if isinstance(new_out, free_variable):
+				lambda_func(
+					self.input,
+					new_out
+				).expand(macro_table)
+
+		elif isinstance(self.output, lambda_func):
+			new_out = self.output.expand(macro_table)
+		elif isinstance(self.output, lambda_apply):
+			new_out = self.output.expand(macro_table)
+		return lambda_func(
+			self.input,
+			new_out
+		)
+
+	def apply(
+			self,
+			val,
+			*,
+			bound_var: bound_variable | None = None
+		):
+		"""
+		Substitute `bound_var` into all instances of a bound variable `var`.
+		If `bound_var` is none, use this functions bound variable.
+		Returns a new object.
+		"""
+
+		calling_self = False
+		if bound_var is None:
+			calling_self = True
+			bound_var = self.input
+		new_out = self.output
+		if isinstance(self.output, bound_variable):
+			if self.output == bound_var:
+				new_out = val
+		elif isinstance(self.output, lambda_func):
+			new_out = self.output.apply(val, bound_var = bound_var)
+		elif isinstance(self.output, lambda_apply):
+			new_out = self.output.sub_bound_var(val, bound_var = bound_var)
+		else:
+			raise TypeError("Cannot apply a function to {self.output!r}")
+
+		# If we're applying THIS function,
+		# just give the output
+		if calling_self:
+			return new_out
+
+		# If we're applying another function,
+		# return this one with substitutions
+		else:
+			return lambda_func(
+				self.input,
+				new_out
+			)
+
+
+class lambda_apply:
+	"""
+	Represents a function application.
+	Has two elements: fn, the function,
+	and arg, the thing it acts upon.
+
+	Parentheses are handled by the parser, and
+	chained functions are handled by from_parse.
+	"""
+
+	@staticmethod
+	def from_parse(result):
+		if len(result) == 2:
+			return lambda_apply(
+				result[0],
+				result[1]
+			)
+		elif len(result) > 2:
+			return lambda_apply.from_parse([
+				lambda_apply(
+					result[0],
+					result[1]
+				)] + result[2:]
+			)
+
+	def __init__(
+			self,
+			fn,
+			arg
+		):
+		self.fn = fn
+		self.arg = arg
+
+	def __repr__(self) -> str:
+		return f"<{self.fn!r} | {self.arg!r}>"
+
+	def __str__(self) -> str:
+		return f"({self.fn} {self.arg})"
+
+	def bind_variables(
+			self,
+			placeholder: macro | None = None,
+			val: bound_variable | None = None
+		) -> None:
+		"""
+		Does exactly what lambda_func.bind_variables does,
+		but acts on applications instead.
+
+		There will be little documentation in this method,
+		see lambda_func.bind_variables.
+		"""
+
+		if (placeholder is None) and (val != placeholder):
+			raise Exception(
+				"Error while binding variables: placeholder and val are both None."
+			)
+
+		# If val and placeholder are None,
+		# everything below should still work as expected.
+		if isinstance(self.fn, macro) and placeholder is not None:
+			if self.fn == placeholder:
+				self.fn = val
+		elif isinstance(self.fn, lambda_func):
+			self.fn.bind_variables(placeholder, val)
+		elif isinstance(self.fn, lambda_apply):
+			self.fn.bind_variables(placeholder, val)
+
+		if isinstance(self.arg, macro) and placeholder is not None:
+			if self.arg == placeholder:
+				self.arg = val
+		elif isinstance(self.arg, lambda_func):
+			self.arg.bind_variables(placeholder, val)
+		elif isinstance(self.arg, lambda_apply):
+			self.arg.bind_variables(placeholder, val)
+
+	def sub_bound_var(
+		self,
+		val,
+		*,
+		bound_var: bound_variable
+	):
+
+		new_fn = self.fn
+		if isinstance(self.fn, bound_variable):
+			if self.fn == bound_var:
+				new_fn = val
+		elif isinstance(self.fn, lambda_func):
+			new_fn = self.fn.apply(val, bound_var = bound_var)
+		elif isinstance(self.fn, lambda_apply):
+			new_fn = self.fn.sub_bound_var(val, bound_var = bound_var)
+
+		new_arg = self.arg
+		if isinstance(self.arg, bound_variable):
+			if self.arg == bound_var:
+				new_arg = val
+		elif isinstance(self.arg, lambda_func):
+			new_arg = self.arg.apply(val, bound_var = bound_var)
+		elif isinstance(self.arg, lambda_apply):
+			new_arg = self.arg.sub_bound_var(val, bound_var = bound_var)
+
+		return lambda_apply(
+			new_fn,
+			new_arg
+		)
+
+	def expand(self, macro_table = {}):
+		# If fn is a function, apply it.
+		if isinstance(self.fn, lambda_func):
+			return self.fn.apply(self.arg)
+		# If fn is an application or macro, expand it.
+		elif isinstance(self.fn, macro):
+			f = lambda_apply(
+				m := self.fn.expand(macro_table),
+				self.arg
+			)
+
+			# If a macro becomes a free variable,
+			# expand twice.
+			if isinstance(m, free_variable):
+				return f.expand(macro_table)
+			else:
+				return f
+
+		elif isinstance(self.fn, lambda_apply):
+			return lambda_apply(
+				self.fn.expand(macro_table),
+				self.arg
+			)
+
+		# If we get to this point, the function we're applying
+		# can't be expanded. That means it's a free or bound
+		# variable. If that happens, expand the arg instead.
+		elif (
+			isinstance(self.arg, lambda_apply) or
+			isinstance(self.arg, lambda_func)
+		):
+			return lambda_apply(
+				self.fn,
+				self.arg.expand(macro_table)
+			)
+
+		return self
\ No newline at end of file