diff --git a/artiq/unparse.py b/artiq/unparse.py
new file mode 100644
index 000000000..be280132f
--- /dev/null
+++ b/artiq/unparse.py
@@ -0,0 +1,564 @@
+import sys
+import ast
+import os
+
+# Large float and imaginary literals get turned into infinities in the AST.
+# We unparse those infinities to INFSTR.
+INFSTR = "1e" + repr(sys.float_info.max_10_exp + 1)
+
+def interleave(inter, f, seq):
+	"""Call f on each item in seq, calling inter() in between.
+	"""
+	seq = iter(seq)
+	try:
+		f(next(seq))
+	except StopIteration:
+		pass
+	else:
+		for x in seq:
+			inter()
+			f(x)
+
+class Unparser:
+	"""Methods in this class recursively traverse an AST and
+	output source code for the abstract syntax; original formatting
+	is disregarded. """
+
+	def __init__(self, tree, file = sys.stdout):
+		"""Unparser(tree, file=sys.stdout) -> None.
+		 Print the source for tree to file."""
+		self.f = file
+		self._indent = 0
+		self.dispatch(tree)
+		print("", file=self.f)
+		self.f.flush()
+
+	def fill(self, text = ""):
+		"Indent a piece of text, according to the current indentation level"
+		self.f.write("\n"+"    "*self._indent + text)
+
+	def write(self, text):
+		"Append a piece of text to the current line."
+		self.f.write(text)
+
+	def enter(self):
+		"Print ':', and increase the indentation."
+		self.write(":")
+		self._indent += 1
+
+	def leave(self):
+		"Decrease the indentation level."
+		self._indent -= 1
+
+	def dispatch(self, tree):
+		"Dispatcher function, dispatching tree type T to method _T."
+		if isinstance(tree, list):
+			for t in tree:
+				self.dispatch(t)
+			return
+		meth = getattr(self, "_"+tree.__class__.__name__)
+		meth(tree)
+
+
+	############### Unparsing methods ######################
+	# There should be one method per concrete grammar type #
+	# Constructors should be grouped by sum type. Ideally, #
+	# this would follow the order in the grammar, but      #
+	# currently doesn't.                                   #
+	########################################################
+
+	def _Module(self, tree):
+		for stmt in tree.body:
+			self.dispatch(stmt)
+
+	# stmt
+	def _Expr(self, tree):
+		self.fill()
+		self.dispatch(tree.value)
+
+	def _Import(self, t):
+		self.fill("import ")
+		interleave(lambda: self.write(", "), self.dispatch, t.names)
+
+	def _ImportFrom(self, t):
+		self.fill("from ")
+		self.write("." * t.level)
+		if t.module:
+			self.write(t.module)
+		self.write(" import ")
+		interleave(lambda: self.write(", "), self.dispatch, t.names)
+
+	def _Assign(self, t):
+		self.fill()
+		for target in t.targets:
+			self.dispatch(target)
+			self.write(" = ")
+		self.dispatch(t.value)
+
+	def _AugAssign(self, t):
+		self.fill()
+		self.dispatch(t.target)
+		self.write(" "+self.binop[t.op.__class__.__name__]+"= ")
+		self.dispatch(t.value)
+
+	def _Return(self, t):
+		self.fill("return")
+		if t.value:
+			self.write(" ")
+			self.dispatch(t.value)
+
+	def _Pass(self, t):
+		self.fill("pass")
+
+	def _Break(self, t):
+		self.fill("break")
+
+	def _Continue(self, t):
+		self.fill("continue")
+
+	def _Delete(self, t):
+		self.fill("del ")
+		interleave(lambda: self.write(", "), self.dispatch, t.targets)
+
+	def _Assert(self, t):
+		self.fill("assert ")
+		self.dispatch(t.test)
+		if t.msg:
+			self.write(", ")
+			self.dispatch(t.msg)
+
+	def _Global(self, t):
+		self.fill("global ")
+		interleave(lambda: self.write(", "), self.write, t.names)
+
+	def _Nonlocal(self, t):
+		self.fill("nonlocal ")
+		interleave(lambda: self.write(", "), self.write, t.names)
+
+	def _Yield(self, t):
+		self.write("(")
+		self.write("yield")
+		if t.value:
+			self.write(" ")
+			self.dispatch(t.value)
+		self.write(")")
+
+	def _YieldFrom(self, t):
+		self.write("(")
+		self.write("yield from")
+		if t.value:
+			self.write(" ")
+			self.dispatch(t.value)
+		self.write(")")
+
+	def _Raise(self, t):
+		self.fill("raise")
+		if not t.exc:
+			assert not t.cause
+			return
+		self.write(" ")
+		self.dispatch(t.exc)
+		if t.cause:
+			self.write(" from ")
+			self.dispatch(t.cause)
+
+	def _Try(self, t):
+		self.fill("try")
+		self.enter()
+		self.dispatch(t.body)
+		self.leave()
+		for ex in t.handlers:
+			self.dispatch(ex)
+		if t.orelse:
+			self.fill("else")
+			self.enter()
+			self.dispatch(t.orelse)
+			self.leave()
+		if t.finalbody:
+			self.fill("finally")
+			self.enter()
+			self.dispatch(t.finalbody)
+			self.leave()
+
+	def _ExceptHandler(self, t):
+		self.fill("except")
+		if t.type:
+			self.write(" ")
+			self.dispatch(t.type)
+		if t.name:
+			self.write(" as ")
+			self.write(t.name)
+		self.enter()
+		self.dispatch(t.body)
+		self.leave()
+
+	def _ClassDef(self, t):
+		self.write("\n")
+		for deco in t.decorator_list:
+			self.fill("@")
+			self.dispatch(deco)
+		self.fill("class "+t.name)
+		self.write("(")
+		comma = False
+		for e in t.bases:
+			if comma: self.write(", ")
+			else: comma = True
+			self.dispatch(e)
+		for e in t.keywords:
+			if comma: self.write(", ")
+			else: comma = True
+			self.dispatch(e)
+		if t.starargs:
+			if comma: self.write(", ")
+			else: comma = True
+			self.write("*")
+			self.dispatch(t.starargs)
+		if t.kwargs:
+			if comma: self.write(", ")
+			else: comma = True
+			self.write("**")
+			self.dispatch(t.kwargs)
+		self.write(")")
+
+		self.enter()
+		self.dispatch(t.body)
+		self.leave()
+
+	def _FunctionDef(self, t):
+		self.write("\n")
+		for deco in t.decorator_list:
+			self.fill("@")
+			self.dispatch(deco)
+		self.fill("def "+t.name + "(")
+		self.dispatch(t.args)
+		self.write(")")
+		if t.returns:
+			self.write(" -> ")
+			self.dispatch(t.returns)
+		self.enter()
+		self.dispatch(t.body)
+		self.leave()
+
+	def _For(self, t):
+		self.fill("for ")
+		self.dispatch(t.target)
+		self.write(" in ")
+		self.dispatch(t.iter)
+		self.enter()
+		self.dispatch(t.body)
+		self.leave()
+		if t.orelse:
+			self.fill("else")
+			self.enter()
+			self.dispatch(t.orelse)
+			self.leave()
+
+	def _If(self, t):
+		self.fill("if ")
+		self.dispatch(t.test)
+		self.enter()
+		self.dispatch(t.body)
+		self.leave()
+		# collapse nested ifs into equivalent elifs.
+		while (t.orelse and len(t.orelse) == 1 and
+			   isinstance(t.orelse[0], ast.If)):
+			t = t.orelse[0]
+			self.fill("elif ")
+			self.dispatch(t.test)
+			self.enter()
+			self.dispatch(t.body)
+			self.leave()
+		# final else
+		if t.orelse:
+			self.fill("else")
+			self.enter()
+			self.dispatch(t.orelse)
+			self.leave()
+
+	def _While(self, t):
+		self.fill("while ")
+		self.dispatch(t.test)
+		self.enter()
+		self.dispatch(t.body)
+		self.leave()
+		if t.orelse:
+			self.fill("else")
+			self.enter()
+			self.dispatch(t.orelse)
+			self.leave()
+
+	def _With(self, t):
+		self.fill("with ")
+		interleave(lambda: self.write(", "), self.dispatch, t.items)
+		self.enter()
+		self.dispatch(t.body)
+		self.leave()
+
+	# expr
+	def _Bytes(self, t):
+		self.write(repr(t.s))
+
+	def _Str(self, tree):
+		self.write(repr(tree.s))
+
+	def _Name(self, t):
+		self.write(t.id)
+
+	def _NameConstant(self, t):
+		self.write(repr(t.value))
+
+	def _Num(self, t):
+		# Substitute overflowing decimal literal for AST infinities.
+		self.write(repr(t.n).replace("inf", INFSTR))
+
+	def _List(self, t):
+		self.write("[")
+		interleave(lambda: self.write(", "), self.dispatch, t.elts)
+		self.write("]")
+
+	def _ListComp(self, t):
+		self.write("[")
+		self.dispatch(t.elt)
+		for gen in t.generators:
+			self.dispatch(gen)
+		self.write("]")
+
+	def _GeneratorExp(self, t):
+		self.write("(")
+		self.dispatch(t.elt)
+		for gen in t.generators:
+			self.dispatch(gen)
+		self.write(")")
+
+	def _SetComp(self, t):
+		self.write("{")
+		self.dispatch(t.elt)
+		for gen in t.generators:
+			self.dispatch(gen)
+		self.write("}")
+
+	def _DictComp(self, t):
+		self.write("{")
+		self.dispatch(t.key)
+		self.write(": ")
+		self.dispatch(t.value)
+		for gen in t.generators:
+			self.dispatch(gen)
+		self.write("}")
+
+	def _comprehension(self, t):
+		self.write(" for ")
+		self.dispatch(t.target)
+		self.write(" in ")
+		self.dispatch(t.iter)
+		for if_clause in t.ifs:
+			self.write(" if ")
+			self.dispatch(if_clause)
+
+	def _IfExp(self, t):
+		self.write("(")
+		self.dispatch(t.body)
+		self.write(" if ")
+		self.dispatch(t.test)
+		self.write(" else ")
+		self.dispatch(t.orelse)
+		self.write(")")
+
+	def _Set(self, t):
+		assert(t.elts) # should be at least one element
+		self.write("{")
+		interleave(lambda: self.write(", "), self.dispatch, t.elts)
+		self.write("}")
+
+	def _Dict(self, t):
+		self.write("{")
+		def write_pair(pair):
+			(k, v) = pair
+			self.dispatch(k)
+			self.write(": ")
+			self.dispatch(v)
+		interleave(lambda: self.write(", "), write_pair, zip(t.keys, t.values))
+		self.write("}")
+
+	def _Tuple(self, t):
+		self.write("(")
+		if len(t.elts) == 1:
+			(elt,) = t.elts
+			self.dispatch(elt)
+			self.write(",")
+		else:
+			interleave(lambda: self.write(", "), self.dispatch, t.elts)
+		self.write(")")
+
+	unop = {"Invert":"~", "Not": "not", "UAdd":"+", "USub":"-"}
+	def _UnaryOp(self, t):
+		self.write("(")
+		self.write(self.unop[t.op.__class__.__name__])
+		self.write(" ")
+		self.dispatch(t.operand)
+		self.write(")")
+
+	binop = { "Add":"+", "Sub":"-", "Mult":"*", "Div":"/", "Mod":"%",
+					"LShift":"<<", "RShift":">>", "BitOr":"|", "BitXor":"^", "BitAnd":"&",
+					"FloorDiv":"//", "Pow": "**"}
+	def _BinOp(self, t):
+		self.write("(")
+		self.dispatch(t.left)
+		self.write(" " + self.binop[t.op.__class__.__name__] + " ")
+		self.dispatch(t.right)
+		self.write(")")
+
+	cmpops = {"Eq":"==", "NotEq":"!=", "Lt":"<", "LtE":"<=", "Gt":">", "GtE":">=",
+						"Is":"is", "IsNot":"is not", "In":"in", "NotIn":"not in"}
+	def _Compare(self, t):
+		self.write("(")
+		self.dispatch(t.left)
+		for o, e in zip(t.ops, t.comparators):
+			self.write(" " + self.cmpops[o.__class__.__name__] + " ")
+			self.dispatch(e)
+		self.write(")")
+
+	boolops = {ast.And: 'and', ast.Or: 'or'}
+	def _BoolOp(self, t):
+		self.write("(")
+		s = " %s " % self.boolops[t.op.__class__]
+		interleave(lambda: self.write(s), self.dispatch, t.values)
+		self.write(")")
+
+	def _Attribute(self,t):
+		self.dispatch(t.value)
+		# Special case: 3.__abs__() is a syntax error, so if t.value
+		# is an integer literal then we need to either parenthesize
+		# it or add an extra space to get 3 .__abs__().
+		if isinstance(t.value, ast.Num) and isinstance(t.value.n, int):
+			self.write(" ")
+		self.write(".")
+		self.write(t.attr)
+
+	def _Call(self, t):
+		self.dispatch(t.func)
+		self.write("(")
+		comma = False
+		for e in t.args:
+			if comma: self.write(", ")
+			else: comma = True
+			self.dispatch(e)
+		for e in t.keywords:
+			if comma: self.write(", ")
+			else: comma = True
+			self.dispatch(e)
+		if t.starargs:
+			if comma: self.write(", ")
+			else: comma = True
+			self.write("*")
+			self.dispatch(t.starargs)
+		if t.kwargs:
+			if comma: self.write(", ")
+			else: comma = True
+			self.write("**")
+			self.dispatch(t.kwargs)
+		self.write(")")
+
+	def _Subscript(self, t):
+		self.dispatch(t.value)
+		self.write("[")
+		self.dispatch(t.slice)
+		self.write("]")
+
+	def _Starred(self, t):
+		self.write("*")
+		self.dispatch(t.value)
+
+	# slice
+	def _Ellipsis(self, t):
+		self.write("...")
+
+	def _Index(self, t):
+		self.dispatch(t.value)
+
+	def _Slice(self, t):
+		if t.lower:
+			self.dispatch(t.lower)
+		self.write(":")
+		if t.upper:
+			self.dispatch(t.upper)
+		if t.step:
+			self.write(":")
+			self.dispatch(t.step)
+
+	def _ExtSlice(self, t):
+		interleave(lambda: self.write(', '), self.dispatch, t.dims)
+
+	# argument
+	def _arg(self, t):
+		self.write(t.arg)
+		if t.annotation:
+			self.write(": ")
+			self.dispatch(t.annotation)
+
+	# others
+	def _arguments(self, t):
+		first = True
+		# normal arguments
+		defaults = [None] * (len(t.args) - len(t.defaults)) + t.defaults
+		for a, d in zip(t.args, defaults):
+			if first:first = False
+			else: self.write(", ")
+			self.dispatch(a)
+			if d:
+				self.write("=")
+				self.dispatch(d)
+
+		# varargs, or bare '*' if no varargs but keyword-only arguments present
+		if t.vararg or t.kwonlyargs:
+			if first:first = False
+			else: self.write(", ")
+			self.write("*")
+			if t.vararg:
+				self.write(t.vararg.arg)
+				if t.vararg.annotation:
+					self.write(": ")
+					self.dispatch(t.vararg.annotation)
+
+		# keyword-only arguments
+		if t.kwonlyargs:
+			for a, d in zip(t.kwonlyargs, t.kw_defaults):
+				if first:first = False
+				else: self.write(", ")
+				self.dispatch(a),
+				if d:
+					self.write("=")
+					self.dispatch(d)
+
+		# kwargs
+		if t.kwarg:
+			if first:first = False
+			else: self.write(", ")
+			self.write("**"+t.kwarg.arg)
+			if t.kwarg.annotation:
+				self.write(": ")
+				self.dispatch(t.kwarg.annotation)
+
+	def _keyword(self, t):
+		self.write(t.arg)
+		self.write("=")
+		self.dispatch(t.value)
+
+	def _Lambda(self, t):
+		self.write("(")
+		self.write("lambda ")
+		self.dispatch(t.args)
+		self.write(": ")
+		self.dispatch(t.body)
+		self.write(")")
+
+	def _alias(self, t):
+		self.write(t.name)
+		if t.asname:
+			self.write(" as "+t.asname)
+
+	def _withitem(self, t):
+		self.dispatch(t.context_expr)
+		if t.optional_vars:
+			self.write(" as ")
+			self.dispatch(t.optional_vars)