Is a record with all optional fields valid in v10?

, ,
1 
// compiles successfully
type a = {
  href?: string
}

Creating an empty record “out of it” is of course not possible:

let x = {}
// or the suggestive annotation
let x : a = {}
// raises
// Error: This let-binding misses an expression

Is it correct to conclude that the experimental optional record fields introduced in v10 (ReScript 10.0 | ReScript Blog) cannot create objects with all optional fields?

2

Empty record is introduced in 10.1, which is not released yet. But available as rescript@next.

2 Likes
3

That’s great!

I wonder what the semantics of specifying an empty record are.

I just installed rescript@next, but after restarting the LSP (and VS Code), the following snippet still gives an error:

type attrs = {class?: string}
@module("@hyperapp/html") @val external aside: (attrs, array<vnode>) => vnode = "aside"
open Hyperapp.Html
let _ = aside({}, [text("Contact info"])
               ~  
// Error (squiggly red under the closing brace of the empty {}): Missing expression
4

This self-contained example works for me:

type attrs = {class?: string}
type vnode
module Hyperapp = {
  module Html = {}
}
let text = (_) => assert false
@module("@hyperapp/html") @val external aside: (attrs, array<vnode>) => vnode = "aside"
open Hyperapp.Html
let _ = aside({}, [text("Contact info")])

package.json:

"dependencies": {
    "rescript": "^10.1.0-alpha.2"
  }
2 Likes
5

Started working for me too. Thank you.

P.S.:This feature still raises the above mentioned error under the extension v1.6.0. I upgraded to the pre-release version and now the error is gone. So until rescript v10.1 stable lands, rescript@latest along with rescript-vscode pre-release should do the job.

1 Like