From the F# interactive, why would it not accept this?

Answer 1

even simpler, just indent your class body...

> type MyCell(n:int) =
-     let mutable data = n + 1
...

Answer 2

It looks like to:

> type MyCell(n:int) =
- let mutable data = n + 1

is not respecting the indentation. F# is whitespace sensitive by default, so you must keep any indentation. Try instead:

> type MyCell(n:int) =
-     let mutable data = n + 1
-     // etc.

(You can make F# non-whitespace sensitive by adding #light "off" at the top of the file, then you need to use extra keywords, as per danben's answer).

Answer 3

1. As pblassucci said, you need to indent your class's contents.
2. Print and ToString are methods, but Data is a property, so for Data the = comes before the definitions of the get and set methods.
3. Instead of always using an identifier like this to refer to the class whose members are being defined, F# lets you choose an identifier on a member-by-member basis. x is used in many examples, but the choice is arbitrary.