hubFS: THE place for F#

Hi,

I am trying to evaluate the following in F# interactive version 1.9.4.17:

> string.Format("{0} {1}", [| "abc" ; "def" |]);;
System.FormatException: Index (zero based) must be greater than or equal to zero and less than the size of the argument list.
   at System.Text.StringBuilder.AppendFormat(IFormatProvider provider, String format, Object[] args)
   at System.String.Format(IFormatProvider provider, String format, Object[] args)
   at <StartupCode$FSI_0132>.$FSI_0132._main()
stopped due to error

Can anyone point me what is wrong here?

Thanks,
dabd

The array argument is an array of ints not objects, hence the String.Format(string, obj) overload is called, not  String.Format(string, obj[])). Try this instead:


string.Format("{0} {1}", Array.map box [|"abc"; "def"|])

This would be the same in C#, btw. Also note that in F# "sprintf" gives you a properly typed formatted-printing function.

Best regards,
  Stephan

I turned to using sprintf but I stumbled on another problem.

I have a fairly big format string and I would like to do something like:

#light
let format_string = "let's say this is my big format string just to say %s"
sprintf format_string "Hello!"

But this is not correct.  How can I build a format string for sprintf?

Thanks.

Because of some compiler magic that goes not the format string needs to be next to the printf function. The idiomatic F# solution to constraint is to create format functions:

#light
let myformater = sprintf "let's say this is my big format string just to say %s"
let mystring = myformater "Hello!"

But if you really want you string to be seperate you can use a type anontation:

let (format_string:Printf.StringFormat<string->string>) = "let's say this is my big format string just to say %s"
sprintf format_string "Hello!"

---

Robert Pickering, MVP
http://strangelights.com