Prep to switch from Def to CExp for backend passes.

src/Lib/TCO.newt

@@ -0,0 +1,44 @@
+module Lib.TCO
+
+import Prelude
+import Data.Graph
+import Lib.Ref2
+import Lib.Common
+import Lib.Types
+import Lib.CompileExp
+
+-- We need CompileExp here, so we know if it's
+-- fully applied, needs eta, etc.
+-- Maybe we should move Ref2 Defs over to CExp?
+-- But we'll need CExp for constructors, etc.
+-- I _could_ collect a stack and look up arity, but
+-- at the next stage, we'd need to fake up constructor
+-- records
+
+tailNames : CExp → List Name
+-- This is tricky, we need to skip the first CLam, but
+-- a deeper one is a return value
+tailNames (CApp (CRef name) args 0) = name :: Nil
+tailNames (CCase _ alts) = join $ map altTailNames alts
+  where
+    altTailNames : CAlt → List Name
+    altTailNames (CConAlt _ _ exp) = tailNames exp
+    altTailNames (CDefAlt exp) = tailNames exp
+    altTailNames (CLitAlt _ exp) = tailNames exp
+tailNames (CLet _ _ t) = tailNames t
+tailNames (CLetRec _ _ t) = tailNames t
+tailNames (CConstr _ args) = join $ map tailNames args
+tailNames (CBnd _) = Nil
+tailNames (CFun _ _) = Nil
+tailNames (CLam _ _) = Nil
+tailNames (CApp t args n) = Nil
+tailNames (CRef _) = Nil
+tailNames CErased = Nil
+tailNames (CLit _) = Nil
+tailNames (CMeta _) = Nil
+tailNames (CRaw _) = Nil
+
+tailCallOpt : {{Ref2 Defs St}} → M Unit
+tailCallOpt = do
+  defs <- getRef Defs
+  putStrLn "TODO TCO"