diff --git a/fco/Makefile b/fco/Makefile
index dca588e..47995fe 100644
--- a/fco/Makefile
+++ b/fco/Makefile
@@ -1,5 +1,8 @@
 all: fco
 
-fco: Main.hs Parse.hs Tree.hs Pass.hs PhaseSource.hs PhaseOutput.hs
+fco: Main.hs Parse.hs Tree.hs Pass.hs PhaseSource.hs PhaseOutput.hs BasePasses.hs
 	ghc -o fco --make Main
 
+BasePasses.hs: Tree.hs make-passthrough.py
+	python make-passthrough.py
+
diff --git a/fco/PhaseOutput.hs b/fco/PhaseOutput.hs
index f1d362b..6a37a68 100644
--- a/fco/PhaseOutput.hs
+++ b/fco/PhaseOutput.hs
@@ -4,23 +4,15 @@ module PhaseOutput (phaseOutput) where
 
 import Tree
 import Pass
-import PhaseSource
+import BasePasses
 
 phaseOutput
   = (Phase "C output"
-      [basePass1, basePass9]
+      [basePassOc, basePassC]
       [
         ("Convert expressions", convExpressions)
       ])
 
--- {{{ BEGIN basePass9
-basePass9 :: Pass
-basePass9 next top node
-  = case node of
-      CCode a -> CCode a
-      _ -> next node
--- }}} END
-
 convExpressions :: Pass
 convExpressions next top node
   = case node of
diff --git a/fco/PhaseSource.hs b/fco/PhaseSource.hs
index dd24434..d4c38f5 100644
--- a/fco/PhaseSource.hs
+++ b/fco/PhaseSource.hs
@@ -1,145 +1,18 @@
 -- Source-rewriting passes
 
-module PhaseSource (phaseSource, basePass1) where
+module PhaseSource (phaseSource) where
 
 import Tree
 import Pass
+import BasePasses
 
 phaseSource
   = (Phase "Source rewriting"
-      [basePass1]
+      [basePassOc]
       [
         ("C-ify identifiers", cifyIdentifiers)
       ])
 
--- {{{ BEGIN basePass1
-basePass1 :: Pass
-basePass1 next top node
-  = case node of
-      OcDecl a b -> OcDecl (top a) (top b)
-      OcAlt a -> OcAlt (map top a)
-      OcAltRep a b -> OcAltRep (top a) (top b)
-      OcPriAlt a -> OcPriAlt (map top a)
-      OcPriAltRep a b -> OcPriAltRep (top a) (top b)
-      OcIn a b -> OcIn (top a) (map top b)
-      OcVariant a b -> OcVariant (top a) (top b)
-      OcInCase a b -> OcInCase (top a) (map top b)
-      OcInCaseGuard a b c -> OcInCaseGuard (top a) (top b) (map top c)
-      OcInTag a b -> OcInTag (top a) (top b)
-      OcOut a b -> OcOut (top a) (map top b)
-      OcOutCase a b c -> OcOutCase (top a) (top b) (map top c)
-      OcExpList a -> OcExpList (map top a)
-      OcAssign a b -> OcAssign (map top a) (top b)
-      OcIf a -> OcIf (map top a)
-      OcIfRep a b -> OcIfRep (top a) (top b)
-      OcInAfter a b -> OcInAfter (top a) (top b)
-      OcWhile a b -> OcWhile (top a) (top b)
-      OcPar a -> OcPar (map top a)
-      OcParRep a b -> OcParRep (top a) (top b)
-      OcPriPar a -> OcPriPar (map top a)
-      OcPriParRep a b -> OcPriParRep (top a) (top b)
-      OcPlacedPar a -> OcPlacedPar (map top a)
-      OcPlacedParRep a b -> OcPlacedParRep (top a) (top b)
-      OcProcessor a b -> OcProcessor (top a) (top b)
-      OcSkip -> OcSkip
-      OcStop -> OcStop
-      OcCase a b -> OcCase (top a) (map top b)
-      OcSeq a -> OcSeq (map top a)
-      OcSeqRep a b -> OcSeqRep (top a) (top b)
-      OcProcCall a b -> OcProcCall (top a) (map top b)
-      OcMainProcess -> OcMainProcess
-      OcVars a b -> OcVars (top a) (map top b)
-      OcIs a b -> OcIs (top a) (top b)
-      OcIsType a b c -> OcIsType (top a) (top b) (top c)
-      OcValIs a b -> OcValIs (top a) (top b)
-      OcValIsType a b c -> OcValIsType (top a) (top b) (top c)
-      OcPlace a b -> OcPlace (top a) (top b)
-      OcDataType a b -> OcDataType (top a) (top b)
-      OcRecord a -> OcRecord (map top a)
-      OcPackedRecord a -> OcPackedRecord (map top a)
-      OcFields a b -> OcFields (top a) (map top b)
-      OcProtocol a b -> OcProtocol (top a) (map top b)
-      OcTaggedProtocol a b -> OcTaggedProtocol (top a) (map top b)
-      OcTag a b -> OcTag (top a) (map top b)
-      OcFormal a b -> OcFormal (top a) (top b)
-      OcProc a b c -> OcProc (top a) (map top b) (top c)
-      OcFunc a b c d -> OcFunc (top a) (map top b) (map top c) (top d)
-      OcFuncIs a b c d -> OcFuncIs (top a) (map top b) (map top c) (top d)
-      OcRetypes a b c -> OcRetypes (top a) (top b) (top c)
-      OcValRetypes a b c -> OcValRetypes (top a) (top b) (top c)
-      OcReshapes a b c -> OcReshapes (top a) (top b) (top c)
-      OcValReshapes a b c -> OcValReshapes (top a) (top b) (top c)
-      OcValOf a b -> OcValOf (top a) (top b)
-      OcSub a b -> OcSub (top a) (top b)
-      OcSubFromFor a b c -> OcSubFromFor (top a) (top b) (top c)
-      OcSubFrom a b -> OcSubFrom (top a) (top b)
-      OcSubFor a b -> OcSubFor (top a) (top b)
-      OcCaseExps a b -> OcCaseExps (map top a) (top b)
-      OcElse a -> OcElse (top a)
-      OcFor a b c -> OcFor (top a) (top b) (top c)
-      OcConv a b -> OcConv (top a) (top b)
-      OcRound a b -> OcRound (top a) (top b)
-      OcTrunc a b -> OcTrunc (top a) (top b)
-      OcAdd a b -> OcAdd (top a) (top b)
-      OcSubtr a b -> OcSubtr (top a) (top b)
-      OcMul a b -> OcMul (top a) (top b)
-      OcDiv a b -> OcDiv (top a) (top b)
-      OcMod a b -> OcMod (top a) (top b)
-      OcRem a b -> OcRem (top a) (top b)
-      OcPlus a b -> OcPlus (top a) (top b)
-      OcMinus a b -> OcMinus (top a) (top b)
-      OcTimes a b -> OcTimes (top a) (top b)
-      OcBitAnd a b -> OcBitAnd (top a) (top b)
-      OcBitOr a b -> OcBitOr (top a) (top b)
-      OcBitXor a b -> OcBitXor (top a) (top b)
-      OcAnd a b -> OcAnd (top a) (top b)
-      OcOr a b -> OcOr (top a) (top b)
-      OcEq a b -> OcEq (top a) (top b)
-      OcNEq a b -> OcNEq (top a) (top b)
-      OcLess a b -> OcLess (top a) (top b)
-      OcMore a b -> OcMore (top a) (top b)
-      OcLessEq a b -> OcLessEq (top a) (top b)
-      OcMoreEq a b -> OcMoreEq (top a) (top b)
-      OcAfter a b -> OcAfter (top a) (top b)
-      OcMonSub a -> OcMonSub (top a)
-      OcMonBitNot a -> OcMonBitNot (top a)
-      OcMonNot a -> OcMonNot (top a)
-      OcMostPos a -> OcMostPos (top a)
-      OcMostNeg a -> OcMostNeg (top a)
-      OcSize a -> OcSize (top a)
-      OcCall a b -> OcCall (top a) (map top b)
-      OcBytesIn a -> OcBytesIn (top a)
-      OcOffsetOf a b -> OcOffsetOf (top a) (top b)
-      OcGuarded a b -> OcGuarded (top a) (top b)
-      OcVal a -> OcVal (top a)
-      OcChanOf a -> OcChanOf (top a)
-      OcPortOf a -> OcPortOf (top a)
-      OcTimer -> OcTimer
-      OcArray a b -> OcArray (top a) (top b)
-      OcArrayUnsized a -> OcArrayUnsized (top a)
-      OcCounted a b -> OcCounted (top a) (top b)
-      OcBool -> OcBool
-      OcByte -> OcByte
-      OcInt -> OcInt
-      OcInt16 -> OcInt16
-      OcInt32 -> OcInt32
-      OcInt64 -> OcInt64
-      OcReal32 -> OcReal32
-      OcReal64 -> OcReal64
-      OcAny -> OcAny
-      OcTypedLit a b -> OcTypedLit (top a) (top b)
-      OcLitReal a -> OcLitReal a
-      OcLitInt a -> OcLitInt a
-      OcLitHex a -> OcLitHex a
-      OcLitByte a -> OcLitByte a
-      OcLitString a -> OcLitString a
-      OcLitArray a -> OcLitArray (map top a)
-      OcTrue -> OcTrue
-      OcFalse -> OcFalse
-      OcName a -> OcName a
-      _ -> next node
--- }}} END
-
 cifyIdentifiers :: Pass
 cifyIdentifiers next top node
   = case node of
diff --git a/fco/Tree.hs b/fco/Tree.hs
index fd4bb69..74c1e96 100644
--- a/fco/Tree.hs
+++ b/fco/Tree.hs
@@ -3,7 +3,7 @@
 module Tree where
 
 data Node =
--- {{{ BEGIN PhaseSource.hs basePass1
+-- {{{ BEGIN basePassOc
   OcDecl Node Node
   | OcAlt [Node]
   | OcAltRep Node Node
@@ -139,7 +139,7 @@ data Node =
   | OcName String
 -- }}} END
 
--- {{{ BEGIN PhaseOutput.hs basePass9
+-- {{{ BEGIN basePassC
   | CCode String
 -- }}} END
 
diff --git a/fco/make-passthrough.py b/fco/make-passthrough.py
index e972a63..3ed1d04 100644
--- a/fco/make-passthrough.py
+++ b/fco/make-passthrough.py
@@ -7,19 +7,8 @@ def die(*s):
 	print >>sys.stderr, "Fatal: " + "".join(map(str, s))
 	sys.exit(1)
 
-def update_def(fn, func, f):
-	origf = open(fn)
-	newf = open(fn + ".new", "w")
-
-	while True:
-		s = origf.readline()
-		if s == "":
-			die("Couldn't find start marker for ", func, " in ", fn)
-		newf.write(s)
-		if s.strip().startswith("-- {{{ BEGIN " + func):
-			break
-
-	newf.write(func + " :: Pass\n")
+def update_def(func, f, newf):
+	newf.write("\n" + func + " :: Pass\n")
 	newf.write(func + " next top node\n")
 	newf.write("  = case node of\n")
 	while True:
@@ -59,29 +48,27 @@ def update_def(fn, func, f):
 		newf.write("      " + name + space + " ".join(lhs) + " -> " + name + space + " ".join(rhs) + "\n")
 	newf.write("      _ -> next node\n")
 
-	while True:
-		s = origf.readline()
-		if s == "":
-			die("Couldn't find end marker for ", func, " in ", fn)
-		if s.strip().startswith("-- }}} END"):
-			newf.write(s)
-			break
-
-	newf.write(origf.read())
-
-	origf.close()
-	newf.close()
-	os.rename(fn + ".new", fn)
-
 def main():
 	f = open("Tree.hs")
+	newf = open("BasePasses.hs", "w")
+
+	newf.write("""-- Base passes
+-- Automatically generated from Tree.hs -- do not edit!
+
+module BasePasses where
+
+import Tree
+import Pass
+""")
+
 	while 1:
 		s = f.readline()
 		if s == "":
 			break
 		if s.startswith("-- {{{ BEGIN"):
 			ss = s.strip().split()
-			update_def(ss[3], ss[4], f)
+			update_def(ss[3], f, newf)
 	f.close()
+	newf.close()
 
 main()