diff --git a/TODO.md b/TODO.md
index b4d5b89..402d0f4 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,9 +1,12 @@
 
 ## TODO
 
+- [ ] "Expected keyword" at `\ a ->` should be error at the `->`
 - [ ] Show Either
 - [ ] `local` for `where`-like `let` clauses? (I want a `where` that closes over more stuff)
-- [ ] Erasure checking happens at compile time and isn't surfaced to editor..
+  - I can do `let f : ... = \ a b c => ...`. But it doesn't work for recursion and cases are awkward.
+- [x] Erasure checking happens at compile time and isn't surfaced to editor..
+- [ ] Erasure issue during AoC from case building replacing a non-erased value with erased.
 - [ ] Add Foldable?
 - [ ] "Failed to unify %var0 and %var1" - get names in there
   - Need fancier `Env`
diff --git a/src/Lib/ProcessDecl.newt b/src/Lib/ProcessDecl.newt
index a5a074b..ebe08b5 100644
--- a/src/Lib/ProcessDecl.newt
+++ b/src/Lib/ProcessDecl.newt
@@ -181,12 +181,17 @@ processDef ns fc nm clauses = do
   -- moved to Compile.newt because it was interfering with type checking (Zoo4eg.newt) via over-reduction
   -- tm' <- zonk top 0 Nil tm
 
+  -- for effect, so we see errors in the editor
+  -- We need to keep the _unerased_ term for checking
+  _ <- erase Nil tm Nil
+
   debug $ \ _ => "Add def \{nm} \{render 90 $ pprint Nil tm} : \{render 90 $ pprint Nil ty}"
   updateDef (QN ns nm) fc ty (Fn tm)
   -- putStrLn "complexity \{show (QN ns nm)} \{show $ complexity tm}"
   -- putStrLn $ show tm
   -- TODO we need some protection against inlining a function calling itself.
   -- We need better heuristics, maybe fuel and deciding while inlining.
+  -- someday users will tag functions as inline, so maybe an explicit loop check
   -- IO,bind is explicit here because the complexity has a 100 in it.
   let name = show $ QN ns nm
   if complexity tm < 15 || name == "Prelude.Prelude.Monad Prelude.IO,bind" || name == "Prelude._>>=_"
diff --git a/tests/aside/Quantity.newt b/tests/Quantity.newt
similarity index 100%
rename from tests/aside/Quantity.newt
rename to tests/Quantity.newt
diff --git a/tests/Quantity.newt.fail b/tests/Quantity.newt.fail
new file mode 100644
index 0000000..32d9669
--- /dev/null
+++ b/tests/Quantity.newt.fail
@@ -0,0 +1,10 @@
+*** Process tests/Quantity.newt
+module Prelude
+module Quantity
+ERROR at tests/Quantity.newt:11:15--11:16: used erased value x$0 (FIXME FC may be wrong here)
+  -- This should fail to compile
+  bar : ∀ x. Nat
+  bar {x} = foo x
+                ^
+
+Compile failed