(module mrb_4_unit_element_reject
  (fn main
    (doc "An LLM author mistakenly names Unit as the element type of a RawBuf. Unit is not in RawBuf's permitted element set {Int, Float, Bool}, so this must be rejected at `ail check` with a param-in diagnostic naming Unit — NOT crash later at build/codegen (the #51 fix). The buffer is only sized and its size printed, so the error is purely the forbidden element type.")
    (type (fn-type (params) (ret (own (con Unit))) (effects IO)))
    (params)
    (body
      (let buf (new RawBuf (con Unit) 4)
        (app print (app RawBuf.size buf))))))