diff --git a/src/Commands.newt b/src/Commands.newt
index 796afe8..903d2e4 100644
--- a/src/Commands.newt
+++ b/src/Commands.newt
@@ -12,19 +12,19 @@ import Lib.Token
 import Lib.Elab
 
 -- For now we cheat and assume capitalized directories are a module component
-decomposeName : String → String × List String
+decomposeName : String → String × String
 decomposeName fn =
     go Nil $ Lin <>< split (fst $ splitFileName fn) "/"
     where
-        go : List String → SnocList String → String × List String
-        go acc Lin = (".", acc)
+        go : List String → SnocList String → String × String
+        go acc Lin = (".", joinBy "." acc)
         go acc (xs :< x) = if isUpper $ strIndex x 0
             then go (x :: acc) xs
-            else (joinBy "/" (xs :< x <>> Nil), acc)
+            else (joinBy "/" (xs :< x <>> Nil), joinBy "." acc)
 
 -- The cheap version of type at point, find the token, lookup in global context
 -- Later we will either get good FC for entries or scan them all and build a cache.
-getHoverInfo : FileSource → List String → Int → Int → M (Maybe (String × FC))
+getHoverInfo : FileSource → String → Int → Int → M (Maybe (String × FC))
 getHoverInfo repo modns row col = do
     mod <- processModule emptyFC repo Nil modns
     -- not necessarily loaded into top... (Maybe push this down into that branch of processModule)
diff --git a/src/LSP.newt b/src/LSP.newt
index 681c72e..276ed7a 100644
--- a/src/LSP.newt
+++ b/src/LSP.newt
@@ -73,7 +73,7 @@ updateFile fn src = unsafePerformIO $ do
     let (Right ((nameFC, modName), _, _)) = partialParse fn parseModHeader emptyMap toks
         | Left (err,toks) => writeIORef state st
 
-    Right (ctx,_) <- (invalidateModule $ split modName ".").runM st.topContext
+    Right (ctx,_) <- (invalidateModule modName).runM st.topContext
         | _ => writeIORef state st
     -- TODO It doesn't have record type, but eta expanding resolves this.  See if there is a quick fix.
     -- modifyIORef state [ topContext := ctx ]
@@ -90,7 +90,7 @@ fcToRange (MkFC uri (MkBounds sr sc er ec)) =
 hoverInfo : String → Int → Int → JSObject
 hoverInfo uri line col = unsafePerformIO $ do
     let (base,modns) = decomposeName uri
-    putStrLn "Hover \{uri} base \{base} mod \{joinBy "." modns}"
+    putStrLn "Hover \{uri} base \{base} mod \{modns}"
     st <- readIORef state
     if (st.baseDir /= base)
         then resetState base
@@ -119,8 +119,9 @@ errorToDiag (Postpone fc qn msg) = errorToDiag $ E fc "Postpone \{show qn} \{msg
 
 checkFile : String → JSObject
 checkFile fn = unsafePerformIO $ do
-    let (base,modns) = decomposeName fn
-    putStrLn "Checking \{fn} base \{base} mod \{joinBy "." modns}"
+    let (base,modName) = decomposeName fn
+
+    putStrLn "Checking \{fn} base \{base} mod \{modName}"
     st <- readIORef state
     if (st.baseDir /= base)
         then resetState base
@@ -128,7 +129,7 @@ checkFile fn = unsafePerformIO $ do
     (Right (top, json)) <- (do
         modifyTop [ errors := Nil ]
         putStrLn "processModule"
-        _ <- processModule emptyFC lspFileSource Nil modns
+        _ <- processModule emptyFC lspFileSource Nil modName
         pure MkUnit
         -- pull out errors and infos
         top <- getTop
diff --git a/src/Lib/Common.newt b/src/Lib/Common.newt
index 03806e5..9084951 100644
--- a/src/Lib/Common.newt
+++ b/src/Lib/Common.newt
@@ -132,8 +132,8 @@ fcCol fc = fc.bnds.startCol
 class HasFC a where
   getFC : a -> FC
 
-primNS : List String
-primNS = ("Prim" :: Nil)
+primNS : String
+primNS = "Prim"
 
 emptyFC : FC
 emptyFC = MkFC "" (MkBounds 0 0 0 0)
@@ -141,10 +141,9 @@ emptyFC = MkFC "" (MkBounds 0 0 0 0)
 emptyFC' : String → FC
 emptyFC' fn = MkFC fn (MkBounds 0 0 0 0)
 
--- Error of a parse
-
+-- Using a String instead of List String for the module shaved about 16% of compile time...
 data QName : U where
-  QN : List String -> String -> QName
+  QN : String -> String -> QName
 
 .baseName : QName → String
 (QN _ name).baseName = name
@@ -154,8 +153,8 @@ instance Eq QName where
   QN ns n == QN ns' n' = if n == n' then ns == ns' else False
 
 instance Show QName where
-  show (QN Nil n) = n
-  show (QN ns n) = joinBy "." ns ++ "." ++ n
+  show (QN "" n) = n
+  show (QN ns n) = ns ++ "." ++ n
 
 instance Ord QName where
   compare (QN ns nm) (QN ns' nm') = if ns == ns' then compare nm nm' else compare ns ns'
diff --git a/src/Lib/CompileExp.newt b/src/Lib/CompileExp.newt
index b4cab63..d9e045a 100644
--- a/src/Lib/CompileExp.newt
+++ b/src/Lib/CompileExp.newt
@@ -157,7 +157,7 @@ compileTerm tm@(App _ _ _) = case funArgs tm of
     applySucc Nil = pure $ CLam "x" $ CPrimOp "+" (CLit $ LInt 1) (CBnd 0)
     applySucc (t :: Nil) = pure $ CPrimOp "+" (CLit $ LInt 1) t
     applySucc _ = error emptyFC "overapplied Succ \{show tm}"
-compileTerm (UU _) = pure $ CRef (QN Nil "U")
+compileTerm (UU _) = pure $ CRef (QN "" "U")
 compileTerm (Pi _ nm icit rig t u) = do
   t' <- compileTerm t
   u' <- compileTerm u
diff --git a/src/Lib/Elab.newt b/src/Lib/Elab.newt
index fe4ca6e..dd38ec6 100644
--- a/src/Lib/Elab.newt
+++ b/src/Lib/Elab.newt
@@ -1549,7 +1549,7 @@ infer ctx tm@(RUpdateRec fc _ _) = do
 infer ctx (RVar fc nm) = go 0 ctx.types
   where
     entryNS : TopEntry → String
-    entryNS (MkEntry fc (QN ns _) _ _ _) = joinBy "." ns
+    entryNS (MkEntry fc (QN ns _) _ _ _) = ns
 
     go : Int -> List (String × Val)  -> M (Tm × Val)
     go i Nil = do
diff --git a/src/Lib/ProcessDecl.newt b/src/Lib/ProcessDecl.newt
index a9f91ec..d17e169 100644
--- a/src/Lib/ProcessDecl.newt
+++ b/src/Lib/ProcessDecl.newt
@@ -100,9 +100,9 @@ checkAlreadyDef fc nm = do
     Just entry => error fc "\{show nm} is already defined at \{show entry.fc}"
 
 
-processDecl : List String -> Decl -> M Unit
+processDecl :  String -> Decl -> M Unit
 
-processTypeSig : List String → FC → List Name → Raw → M Unit
+processTypeSig :  String → FC → List Name → Raw → M Unit
 processTypeSig ns fc names tm = do
   log 1 $ \ _ => "-----"
   top <- getTop
@@ -112,7 +112,7 @@ processTypeSig ns fc names tm = do
   ignore $ for names $ \nm => setDef (QN ns nm) fc ty Axiom Nil
 
 
-processPrimType : List Name → FC → Name → Maybe Raw → M Unit
+processPrimType : String → FC → Name → Maybe Raw → M Unit
 processPrimType ns fc nm ty = do
   top <- getTop
   ty' <- check (mkCtx fc) (maybe (RU fc) id ty) (VU fc)
@@ -120,7 +120,7 @@ processPrimType ns fc nm ty = do
   setDef (QN ns nm) fc ty' (PrimTCon arity) Nil
 
 
-processPrimFn : List String → FC → String → List String → Raw → String → M Unit
+processPrimFn :  String → FC → String → List String → Raw → String → M Unit
 processPrimFn ns fc nm used ty src = do
   top <- getTop
   ty <- check (mkCtx fc) ty (VU fc)
@@ -153,7 +153,7 @@ complexity (Lit _ _) = 0
 complexity (Case _ sc (CaseCons _ _ t :: Nil)) = 1 + complexity sc + complexity t
 complexity _ = 100
 
-processDef : List String → FC → String → List (Raw × Maybe Raw) → M Unit
+processDef :  String → FC → String → List (Raw × Maybe Raw) → M Unit
 processDef ns fc nm clauses = do
   log 1 $ \ _ => "-----"
   log 1 $ \ _ => "Def \{show nm}"
@@ -194,7 +194,7 @@ processDef ns fc nm clauses = do
     then setFlag (QN ns nm) fc Inline
     else pure MkUnit
 
-processCheck : List String → FC → Raw → Raw → M Unit
+processCheck :  String → FC → Raw → Raw → M Unit
 processCheck ns fc tm ty = do
   log 1 $ \ _ => "----- DCheck"
   top <- getTop
@@ -209,7 +209,7 @@ processCheck ns fc tm ty = do
   putStrLn "  NF \{render 90 $ pprint Nil norm}"
 
 
-processClass : List String → FC → (FC × String) → Telescope → List Decl → M Unit
+processClass :  String → FC → (FC × String) → Telescope → List Decl → M Unit
 processClass ns classFC (nameFC, nm) tele decls = do
   -- REVIEW maybe we can leverage Record for this
   -- a couple of catches, we don't want the dotted accessors and
@@ -257,7 +257,7 @@ processClass ns classFC (nameFC, nm) tele decls = do
     mkApp : Raw → BindInfo × Raw → Raw
     mkApp acc (BI fc nm icit _, _) = RApp fc acc (RVar fc nm) icit
 
-processInstance : List String → FC → Raw → Maybe (List Decl) → M Unit
+processInstance :  String → FC → Raw → Maybe (List Decl) → M Unit
 processInstance ns instfc ty decls = do
   log 1 $ \ _ => "-----"
   log 1 $ \ _ => "Instance \{render 90 $ pretty ty}"
@@ -372,7 +372,7 @@ processInstance ns instfc ty decls = do
     apply x (y :: xs) = error instfc "expected pi type \{show x}"
 
 -- desugars to Data and processes it
-processShortData : List String → FC → Raw → List Raw → M Unit
+processShortData :  String → FC → Raw → List Raw → M Unit
 processShortData ns fc lhs sigs = do
   (nameFC, nm,args) <- getArgs lhs Nil
   let ty = foldr mkPi (RU fc) args
@@ -431,7 +431,7 @@ populateConInfo entries =
     isSucc (MkEntry fc nm dty@(Pi _ _ _ _ (Ref _ a) (Ref _ b)) (DCon _ _ (Many :: Nil) hn) _) = a == b
     isSucc _ = False
 
-processData : List String → FC → FC × String → Raw → List Decl → M Unit
+processData : String → FC → FC × String → Raw → List Decl → M Unit
 processData ns fc (nameFC, nm) ty cons = do
   log 1 $ \ _ => "-----"
   log 1 $ \ _ => "Data \{nm}"
@@ -487,7 +487,7 @@ processData ns fc (nameFC, nm) ty cons = do
     checkDeclType _ = error fc "data type doesn't return U"
 
 
-processRecord : List String → FC → FC × String → Telescope → Maybe (FC × Name) → List Decl → M Unit
+processRecord :  String → FC → FC × String → Telescope → Maybe (FC × Name) → List Decl → M Unit
 processRecord ns recordFC (nameFC, nm) tele cname decls = do
   log 1 $ \ _ => "-----"
   log 1 $ \ _ => "Record"
diff --git a/src/Lib/ProcessModule.newt b/src/Lib/ProcessModule.newt
index 4d59240..57965b9 100644
--- a/src/Lib/ProcessModule.newt
+++ b/src/Lib/ProcessModule.newt
@@ -23,10 +23,11 @@ addPrimitives = do
   top <- getTop
   let mod = MkModCtx "" top.defs (MC emptyMap Nil 0 CheckAll) top.ops Nil top.errors
   let modules = updateMap primNS mod top.modules
+  -- TODO - do we clear this? Try just modules := modules, but wait until this refactor is done.
   modifyTop [ modules := modules
       ; imported := primNS :: Nil
       ; hints := emptyMap
-      ; ns := Nil
+      ; ns := ""
       ; defs := emptyMap
       ]
   pure mod
@@ -62,17 +63,17 @@ importHints (entry :: entries) = do
 -- HACK this is returning src to help render errors..
 -- Maybe return module, put src and errors in module, add error for import with error, callers can sort out what they want to do?
 -- The issue here is command line newt wants to report all errors (we can print that though?)  LSP wants something more subtle
-processModule : FC → FileSource → List String → (stack : List String) → M ModContext
+processModule : FC → FileSource → List String → String → M ModContext
 processModule importFC repo stk modns = do
   top <- getTop
-  let name = joinBy "." modns
+
   let (Nothing) = lookupMap' modns top.modules
     | Just mod => pure mod
 
   let (False) = modns == primNS
     | _ => addPrimitives
-
-  let fn = joinBy "/" modns ++ ".newt"
+  let parts = split modns "."
+  let fn = joinBy "/" parts ++ ".newt"
   -- TODO now we can pass in the module name...
   (fn,src) <- repo.getFile importFC fn
   let (Right toks) = tokenise fn src
@@ -82,21 +83,18 @@ processModule importFC repo stk modns = do
     | Left (err, toks) => throwError err
 
   log 1 $ \ _ => "scan imports for module \{modName}"
-  let (True) = modns == split modName "."
+  let (True) = modns == modName
     | _ => throwError $ E nameFC "module name \{show modName} doesn't match file name \{show fn}"
 
   let (Right (imports, ops, toks)) = partialParse fn parseImports ops toks
     | Left (err, toks) => throwError err
 
-  let importNames = map importToName imports
-
   imported <- for imports $ \case
     MkImport fc (nameFC, name') => do
-      let imp = split name' "."
-      when (elem name' stk) $ \ _ => error nameFC "import loop \{show name} → \{show name'}"
-      processModule nameFC repo (name :: stk) imp
-      pure $ imp
-  processModule nameFC repo (name :: stk) primNS
+      when (elem name' stk) $ \ _ => error nameFC "import loop \{modns} → \{name'}"
+      processModule nameFC repo (modns :: stk) name'
+      pure $ name'
+  processModule nameFC repo (modns :: stk) primNS
   let imported = snoc imported primNS
 
   putStrLn "module \{modName}"
@@ -107,6 +105,7 @@ processModule importFC repo stk modns = do
 
   top <- getTop
   let freshMC = MC emptyMap Nil 0 CheckAll
+  -- NOW Print and drop errors here
   -- set imported, mod, freshMC, ops  before processing
   modifyTop [ imported := imported
             ; hints := emptyMap
@@ -125,7 +124,7 @@ processModule importFC repo stk modns = do
   -- update modules with result, leave the rest of context in case this is top file
   top <- getTop
 
-  let mod = MkModCtx src top.defs top.metaCtx top.ops importNames top.errors
+  let mod = MkModCtx src top.defs top.metaCtx top.ops imported top.errors
 
   let modules = updateMap modns mod top.modules
   modifyTop [modules := modules]
@@ -134,11 +133,11 @@ processModule importFC repo stk modns = do
   -- FIXME module context should hold errors, to report in replay
   pure mod
   where
-    tryProcessDecl : String → List String → Decl → M Unit
+    tryProcessDecl : String → String → Decl → M Unit
     tryProcessDecl src ns decl = do
       (Left err) <- tryError $ processDecl ns decl | _ => pure MkUnit
       addError err
 
--- TODO clear dependents too.
-invalidateModule : List String -> M Unit
+-- NOW TODO clear dependents too.
+invalidateModule : String -> M Unit
 invalidateModule modname = modifyTop [modules $= deleteMap modname]
diff --git a/src/Lib/ReplParser.newt b/src/Lib/ReplParser.newt
index a07f63b..6d132d3 100644
--- a/src/Lib/ReplParser.newt
+++ b/src/Lib/ReplParser.newt
@@ -36,7 +36,8 @@ replQN = do
   ident <- uident
   rest <- many $ token Projection
   let name = joinBy "" (ident :: rest)
-  pure $ uncurry QN $ unsnoc $ split1 name "."
+  let (ns,nm) = unsnoc $ split1 name "."
+  pure $ QN (joinBy "." ns) nm
 
 data ArgType = ArgNone | ArgString | ArgIdent | ArgOptInt | ArgQName
 
diff --git a/src/Lib/TCO.newt b/src/Lib/TCO.newt
index a72135f..ea32ff8 100644
--- a/src/Lib/TCO.newt
+++ b/src/Lib/TCO.newt
@@ -65,7 +65,7 @@ rewriteTailCalls nms tm = case tm of
 
 -- the name of our trampoline
 bouncer : QName
-bouncer = QN Nil "bouncer"
+bouncer = QN "" "bouncer"
 
 doOptimize : List (QName × CExp) → M (List (QName × CExp))
 doOptimize fns = do
diff --git a/src/Lib/TopContext.newt b/src/Lib/TopContext.newt
index 14bdd60..58b5df4 100644
--- a/src/Lib/TopContext.newt
+++ b/src/Lib/TopContext.newt
@@ -34,7 +34,7 @@ lookupRaw raw top =
     Just entry => Just entry
     Nothing => go top.imported
   where
-    go : List (List String) → Maybe TopEntry
+    go : List String → Maybe TopEntry
     go Nil = Nothing
     go (ns :: nss) = case lookupMap' ns top.modules of
       Nothing => go nss
@@ -47,7 +47,7 @@ instance Show TopContext where
   show top = "\nContext:\n [\{ joinBy "\n" $ map (show ∘ snd) $ toList top.defs}]"
 
 emptyTop : TopContext
-emptyTop = MkTop emptyMap Nil emptyMap Nil emptyMap (MC emptyMap Nil 0 CheckAll) 0 Nil emptyMap
+emptyTop = MkTop emptyMap Nil emptyMap "" emptyMap (MC emptyMap Nil 0 CheckAll) 0 Nil emptyMap
 
 
 setFlag : QName → FC → EFlag → M Unit
diff --git a/src/Lib/Types.newt b/src/Lib/Types.newt
index c2d96f8..26fa98b 100644
--- a/src/Lib/Types.newt
+++ b/src/Lib/Types.newt
@@ -402,7 +402,7 @@ record ModContext where
   modMetaCtx : MetaContext
   -- longer term maybe drop this, put the operator decls in ctxDefs and collect them on import
   ctxOps : Operators
-  modDeps : List (List String)
+  modDeps : List String
   modErrors : List Error
 
 -- Top level context.
@@ -421,15 +421,13 @@ HintTable = SortedMap QName (List (QName × Tm))
 
 record TopContext where
   constructor MkTop
-  -- maybe we use a String instead of List String for the left of QN
-  -- I'm putting a dummy entry in
-  modules : SortedMap (List String) ModContext
-  imported : List (List String)
+  modules : SortedMap String ModContext
+  imported : List String
   -- TCon name → function name × type
   hints : HintTable
 
   -- current module
-  ns : List String
+  ns : String
   defs : SortedMap QName TopEntry
   metaCtx : MetaContext
 
diff --git a/src/Main.newt b/src/Main.newt
index 1673ac9..424bd4e 100644
--- a/src/Main.newt
+++ b/src/Main.newt
@@ -95,9 +95,9 @@ processFile fn = do
   let modns = split modName "."
   base <- getBaseDir fn nameFC modns
 
-  invalidateModule modns
+  invalidateModule modName
   let repo = dirFileSource base
-  mod <- processModule emptyFC repo Nil modns
+  mod <- processModule emptyFC repo Nil modName
   top <- getTop
 
   showErrors fn mod.modSource
@@ -122,7 +122,7 @@ cmdLine (fn :: args) = do
 browseTop : QName → M Unit
 browseTop qn@(QN ns x) = do
   top <- getTop
-  let ns = snoc ns x
+  let ns = ns ++ "." ++ x
   let (Just mod) = lookupMap' ns top.modules
     | _ => putStrLn "module \{show qn} not loaded"
   go $ listValues mod.modDefs