diff --git a/Main.hs b/Main.hs
index 7a8719a..122a527 100644
--- a/Main.hs
+++ b/Main.hs
@@ -36,7 +36,7 @@ import ParseOccam
 import Pass
 import PreprocessOccam
 import PrettyShow
-import RainParse
+import ParseRain
 import RainPasses
 import SimplifyExprs
 import SimplifyProcs
diff --git a/Makefile b/Makefile
index 9f8a7e8..07da1f1 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,9 @@ targets = tock tocktest
 
 all: $(targets)
 
-sources = $(wildcard *.hs) $(patsubst %.x,%.hs,$(wildcard *.x))
+sources = $(wildcard *.hs frontends/*.hs backends/*.hs transformations/*.hs common/*.hs) $(patsubst %.x,%.hs,$(wildcard frontends/*.x))
+
+builtfiles = $(patsubst %.hs,%.hi,$(sources)) $(patsubst %.hs,%.o,$(sources)) $(patsubst %.x,%.hs,$(wildcard frontends/*.x))
 
 %.hs: %.x
 	alex $<
@@ -12,6 +14,7 @@ ghc_opts = \
 	-fglasgow-exts \
 	-fallow-undecidable-instances \
 	-fwarn-unused-binds \
+	-icommon -itransformations -ifrontends -ibackends \
 	$(profile_opts)
 
 tock: $(sources)
@@ -74,7 +77,7 @@ haddock:
 	@mv doc/index.html-2 doc/index.html
 
 clean:
-	rm -f $(targets) *.o *.hi
+	rm -f $(targets) $(builtfiles)
 
 # Don't delete intermediate files.
 .SECONDARY:
diff --git a/TestMain.hs b/TestMain.hs
index b0980f9..460f95d 100644
--- a/TestMain.hs
+++ b/TestMain.hs
@@ -27,8 +27,8 @@ with this program.  If not, see <http://www.gnu.org/licenses/>.
 -- * "UsageCheckTest"
 module TestMain () where
 
-import qualified RainParseTest (tests)
-import qualified RainPassTest (tests)
+import qualified ParseRainTest (tests)
+import qualified RainPassesTest (tests)
 import qualified UsageCheckTest (tests)
 import qualified PassTest (tests)
 import Test.HUnit
@@ -37,8 +37,8 @@ main :: IO ()
 main = do runTestTT $ TestList
             [
               PassTest.tests
-              ,RainParseTest.tests
-              ,RainPassTest.tests
+              ,ParseRainTest.tests
+              ,RainPassesTest.tests
               ,UsageCheckTest.tests
             ]
           return ()
diff --git a/AnalyseAsm.hs b/backends/AnalyseAsm.hs
similarity index 100%
rename from AnalyseAsm.hs
rename to backends/AnalyseAsm.hs
diff --git a/GenerateC.hs b/backends/GenerateC.hs
similarity index 100%
rename from GenerateC.hs
rename to backends/GenerateC.hs
diff --git a/GenerateCPPCSP.hs b/backends/GenerateCPPCSP.hs
similarity index 100%
rename from GenerateCPPCSP.hs
rename to backends/GenerateCPPCSP.hs
diff --git a/TLP.hs b/backends/TLP.hs
similarity index 100%
rename from TLP.hs
rename to backends/TLP.hs
diff --git a/AST.hs b/common/AST.hs
similarity index 100%
rename from AST.hs
rename to common/AST.hs
diff --git a/CompState.hs b/common/CompState.hs
similarity index 100%
rename from CompState.hs
rename to common/CompState.hs
diff --git a/Errors.hs b/common/Errors.hs
similarity index 100%
rename from Errors.hs
rename to common/Errors.hs
diff --git a/EvalConstants.hs b/common/EvalConstants.hs
similarity index 100%
rename from EvalConstants.hs
rename to common/EvalConstants.hs
diff --git a/EvalLiterals.hs b/common/EvalLiterals.hs
similarity index 100%
rename from EvalLiterals.hs
rename to common/EvalLiterals.hs
diff --git a/Intrinsics.hs b/common/Intrinsics.hs
similarity index 100%
rename from Intrinsics.hs
rename to common/Intrinsics.hs
diff --git a/Metadata.hs b/common/Metadata.hs
similarity index 100%
rename from Metadata.hs
rename to common/Metadata.hs
diff --git a/Pass.hs b/common/Pass.hs
similarity index 100%
rename from Pass.hs
rename to common/Pass.hs
diff --git a/Pattern.hs b/common/Pattern.hs
similarity index 100%
rename from Pattern.hs
rename to common/Pattern.hs
diff --git a/PrettyShow.hs b/common/PrettyShow.hs
similarity index 100%
rename from PrettyShow.hs
rename to common/PrettyShow.hs
diff --git a/TestUtil.hs b/common/TestUtil.hs
similarity index 100%
rename from TestUtil.hs
rename to common/TestUtil.hs
diff --git a/TreeUtil.hs b/common/TreeUtil.hs
similarity index 100%
rename from TreeUtil.hs
rename to common/TreeUtil.hs
diff --git a/Types.hs b/common/Types.hs
similarity index 100%
rename from Types.hs
rename to common/Types.hs
diff --git a/Utils.hs b/common/Utils.hs
similarity index 100%
rename from Utils.hs
rename to common/Utils.hs
diff --git a/LexOccam.x b/frontends/LexOccam.x
similarity index 100%
rename from LexOccam.x
rename to frontends/LexOccam.x
diff --git a/LexRain.x b/frontends/LexRain.x
similarity index 100%
rename from LexRain.x
rename to frontends/LexRain.x
diff --git a/ParseOccam.hs b/frontends/ParseOccam.hs
similarity index 100%
rename from ParseOccam.hs
rename to frontends/ParseOccam.hs
diff --git a/RainParse.hs b/frontends/ParseRain.hs
similarity index 99%
rename from RainParse.hs
rename to frontends/ParseRain.hs
index c92a116..7c830cf 100644
--- a/RainParse.hs
+++ b/frontends/ParseRain.hs
@@ -16,7 +16,7 @@ You should have received a copy of the GNU General Public License along
 with this program.  If not, see <http://www.gnu.org/licenses/>.
 -}
 
-module RainParse where
+module ParseRain where
 
 import qualified Text.ParserCombinators.Parsec.Token as P
 import qualified LexRain as L
diff --git a/RainParseTest.hs b/frontends/ParseRainTest.hs
similarity index 99%
rename from RainParseTest.hs
rename to frontends/ParseRainTest.hs
index 8c98180..a8eefcd 100644
--- a/RainParseTest.hs
+++ b/frontends/ParseRainTest.hs
@@ -16,9 +16,9 @@ You should have received a copy of the GNU General Public License along
 with this program.  If not, see <http://www.gnu.org/licenses/>.
 -}
 
-module RainParseTest (tests) where
+module ParseRainTest (tests) where
 
-import qualified RainParse as RP
+import qualified ParseRain as RP
 import qualified AST as A
 import qualified LexRain as L
 import Text.ParserCombinators.Parsec (runParser,eof)
diff --git a/PreprocessOccam.hs b/frontends/PreprocessOccam.hs
similarity index 100%
rename from PreprocessOccam.hs
rename to frontends/PreprocessOccam.hs
diff --git a/RainPasses.hs b/frontends/RainPasses.hs
similarity index 100%
rename from RainPasses.hs
rename to frontends/RainPasses.hs
diff --git a/RainPassTest.hs b/frontends/RainPassesTest.hs
similarity index 99%
rename from RainPassTest.hs
rename to frontends/RainPassesTest.hs
index c70c952..9574e20 100644
--- a/RainPassTest.hs
+++ b/frontends/RainPassesTest.hs
@@ -18,7 +18,7 @@ with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 -- #ignore-exports
 
-module RainPassTest (tests) where
+module RainPassesTest (tests) where
 
 import Test.HUnit hiding (State)
 import Control.Monad.State as CSM
diff --git a/StructureOccam.hs b/frontends/StructureOccam.hs
similarity index 100%
rename from StructureOccam.hs
rename to frontends/StructureOccam.hs
diff --git a/PassTest.hs b/transformations/PassTest.hs
similarity index 100%
rename from PassTest.hs
rename to transformations/PassTest.hs
diff --git a/SimplifyExprs.hs b/transformations/SimplifyExprs.hs
similarity index 100%
rename from SimplifyExprs.hs
rename to transformations/SimplifyExprs.hs
diff --git a/SimplifyProcs.hs b/transformations/SimplifyProcs.hs
similarity index 100%
rename from SimplifyProcs.hs
rename to transformations/SimplifyProcs.hs
diff --git a/SimplifyTypes.hs b/transformations/SimplifyTypes.hs
similarity index 100%
rename from SimplifyTypes.hs
rename to transformations/SimplifyTypes.hs
diff --git a/Unnest.hs b/transformations/Unnest.hs
similarity index 100%
rename from Unnest.hs
rename to transformations/Unnest.hs
diff --git a/UsageCheck.hs b/transformations/UsageCheck.hs
similarity index 100%
rename from UsageCheck.hs
rename to transformations/UsageCheck.hs
diff --git a/UsageCheckTest.hs b/transformations/UsageCheckTest.hs
similarity index 100%
rename from UsageCheckTest.hs
rename to transformations/UsageCheckTest.hs