I am plodding along with my F# book. I have reached the part where I know enough about the syntax of the language to understand something if I read it – but not enough about the language to be productive and write something useful. A bit of a frustrating place to be.
Needless to say when you are in this state of mind – you end up paging mindlessly through chapters of my F# book with no real incentive to learn anything until you hit “Exceptions”.
Raising an exception explicitly
So lets look at raising an exception explicitly – in C# we would throw the exception, F# is a lot more polite instead of throwing the exception it raises it, …
(raise (System.InvalidOperationException("no thank you")))
quite simple…
Catching an Exception
So I would expect to be able to catch an exception as well – lets look at some C# code first…
try
{
Console.WriteLine("Raise Exception");
throw new InvalidOperationException("no thank you");
}
catch
{
Console.WriteLine("Catch Exception and Carry on..");
}
Console.WriteLine("Carry on...");
Console.ReadLine();
The F# equivalent would go as follows…
open System;
try
Console.WriteLine("Raise Exception")
raise (System.InvalidOperationException("no thank you"))
with
| _ -> Console.WriteLine("Catch Exception and Carry on..")
Console.WriteLine("Carry on...")
Console.ReadLine();
In F# there is a “try, with” and a “try finally”
Finally…
In F# there is a finally block however the “with” and “finally” can’t be combined.
open System;
try
Console.WriteLine("Raise Exception")
raise (System.InvalidOperationException("no thank you"))
finally
Console.WriteLine("Finally carry on...")
Console.ReadLine()