Added η-expander module and removed EAdd from grammar.

src/Expander.hs

@@ -0,0 +1,64 @@
+module Expander where
+
+import TypeChecker.TypeCheckerIr
+import Control.Monad.State
+
+type TExp = T' Exp' Type
+
+type M = State Int
+
+expand :: Program -> Program
+expand (Program defs) = Program (map expandDef defs)
+
+expandDef :: Def -> Def
+expandDef (DBind bind) = DBind $ expandBind bind
+expandDef d            = d
+
+initialState = 0
+
+expandBind :: Bind' Type -> Bind' Type
+expandBind (Bind name args e)
+    = Bind name args $ evalState (expandExp e) initialState
+
+expandExp :: TExp -> M TExp
+expandExp e = do
+    case e of
+        (EApp e1@(e_, _) e2@(_, _), t) -> do
+            let sizeType = arrows t
+            let sizeExp = apps e_
+            let diff = sizeType - sizeExp
+            e1' <- expandExp e1
+            e2' <- expandExp e2
+            apply diff (EApp e1' e2', t)
+        (EVar _, t) -> do
+            let sizeType = arrows t
+            apply sizeType e
+        e -> pure e
+
+apply :: Int -> TExp -> M TExp
+apply n (e, t)
+  | n < 1 = pure (e, t)
+  | otherwise = do
+    fr <- fresh
+    let (TFun t1 t2) = t
+    e' <- apply (n - 1) (EApp (e,t) (EVar fr, t1), t2)
+    pure (EAbs fr e', t)
+
+-- Eerily similar functions
+apps :: Exp -> Int
+apps (EApp _ (e2, _)) = 1 + apps e2
+apps _ = 0
+
+arrows :: Type -> Int
+arrows (TFun _ t2) = 1 + arrows t2
+arrows _ = 0
+
+fresh :: M Ident
+fresh = do
+   n <- get 
+   put (n + 1)
+   return (letters !! n)
+  where
+    letters :: [Ident]
+    letters =
+        map (Ident . ("eta$" ++)) $ [1 ..] >>= flip replicateM ['a' .. 'z']