better parser errors

test_scoping.sui

@@ -1,7 +1,11 @@
 fn test_scoping() -> int do
   let x = 5
   let f = lambda (y) y + 1  # simple lambda
-  f = lambda (z) z+1
+  # f = lambda (z) z+1
   let x = 10  # shadow x
   f(3)  # should work
 end
+
+fn stuff(f: fn(int, int) -> int, v: int) -> int do
+  f(v, v)
+end