strange f# list notation in suave.io

Question

In suave.io we can use choose combinator that has the Types.WebPart list -> Types.WebPart type. Examples from their website show that I can use this combinator like this:

choose
    [ path "/hello" >>= OK "Hello GET"
      path "/goodbye" >>= OK "Good bye GET" ]

This list notation seems strange as it doesn't demand semicolon separating the elements. Yet, I have not been able to use it this way in different context. So the following works:

> choose
    [OK ""
     OK ""];;
val it : Types.WebPart = <fun:choose@47>'

as well as

> choose [OK "" ;OK ""];;
val it : Types.WebPart = <fun:choose@47>

But the following don't compile:

>choose [OK "" OK ""];; //ERROR
> [OK ""
  OK ""];; //ERROR

So, how does this notation work?

Answer 1

If you look at your last example

[OK ""
OK ""]

you should see that the in last line: OK "" is not directly below the OK in the previous line: [OK "" (it's one of to the left)

This should give you a hint ;)

You just have to align the elements in the same column (recommended: just use spaces)

this is why you usually write

[
   OK ""
   OK ""
]

instead of beginning the first element after [ - or some like

[ OK ""
; OK "" ]

too but I think that's not idiomatic F#.

remark

this also works with record syntax:

{
   surname = "Smith"
   givenname = "Adam"
}