Tidy up how Main decides which passes to run.

Since the set of passes that runs now depends on several variables, there's now
an expression which builds a list of passes to run; this should be easier to
extend in the future.

CompState.hs

@@ -31,15 +31,15 @@ import Metadata
 
 -- | Modes that Tock can run in.
 data CompMode = ModeParse | ModeCompile | ModePostC
-  deriving (Show, Data, Typeable)
+  deriving (Show, Data, Typeable, Eq)
 
 -- | Backends that Tock can use.
 data CompBackend = BackendC | BackendCPPCSP
-  deriving (Show, Data, Typeable)
-  
+  deriving (Show, Data, Typeable, Eq)
+
 -- | Frontends that Tock can use.
 data CompFrontend = FrontendOccam | FrontendRain
-  deriving (Show, Data, Typeable)  
+  deriving (Show, Data, Typeable, Eq)
 
 -- | State necessary for compilation.
 data CompState = CompState {

Main.hs

@@ -43,8 +43,8 @@ import SimplifyProcs
 import SimplifyTypes
 import Unnest
 
-passes :: [(String, Pass)]
-passes =
+commonPasses :: [(String, Pass)]
+commonPasses =
   [ ("Simplify types", simplifyTypes)
   , ("Simplify expressions", simplifyExprs)
   , ("Simplify processes", simplifyProcs)
@@ -157,10 +157,14 @@ compile fn
             ModeParse -> return $ show ast1
             ModeCompile ->
               do progress "Passes:"
-                 ast2 <- case csFrontend optsPS of                   
-                   FrontendOccam -> (runPasses passes) ast1
-                   --Run the rain passes, then all the normal occam passes too:
-                   FrontendRain -> ((runPasses rainPasses) ast1) >>= (runPasses passes)
+
+                 let passes
+                       = concat [ commonPasses
+                                , if csFrontend optsPS == FrontendRain
+                                    then rainPasses
+                                    else []
+                                ]
+                 ast2 <- runPasses passes ast1
 
                  debug "{{{ Generate code"
                  let generator