Function app

crates/kernel/src/whnf.rs:3518–3520

(f: AE, a: AE)

      return Ok(Some(self.intern(KExpr::str(joined, blob_addr))));
    }

    if *addr == self.prims.string_dec_eq.addr {
      if args.len() != 2 {
        return Ok(None);
      }
      return self.try_reduce_string_dec_eq(e, &args);