fun : a -> a
fun = { crash "NYI" }

┌───────────────┐
│ TYPE MISMATCH ├─ This expression is used in an ──┐
└┬──────────────┘  unexpected way.                 │
 │                                                 │
 │  fun : a -> a                                   │
 │        ‾                                        │
 └────────────────── /tmp/tmp.LfZsV8HsxC/a.roc:1:7 ┘

    It has the type:

        a

    But you are trying to use it as:

        a