[Ur] Minor question about simple Sql demo

[Stefan Scott]

Hello -

As a learning exercise, I have been studying and modifying the simple Sql
demo here:

http://www.impredicative.com/ur/demo/sql.html

My modified version (which now has two tables: a child table `Thing` and a
parent table `Color`) is here:

https://github.com/StefanScott/UrWeb-demoSql-1

This modified version compiles and runs correctly.

---

Now I tried doing a minor modification.

I noticed that the `delete` function takes two arguments:

  delete id ()

The second argument seemed unnecessary, so I tried removing it.

However, removing the second argument gave a compile error:

  Have con:  int -> transaction (xml ([Html = ()]) ([]) ([]))
  Need con:  int -> {} -> transaction (xml ([Html = ()]) ([]) ([]))

Why does a compile error occur when the second argument to `delete` is
removed?

Thanks for any help!

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