Hi,

I would like to request help from the F# gurus here.

I have defined the following simple function:

*****

exception NullListHeadException;;

let list_head = function

|h :: t -> h

|_ -> raise NullListHeadException;;

*****

Now, calling "list_head [1; 2; 3]" returns "1" as expected. But calling "list_head []" returns the following error message:

*****

stdin(0,1): error FS0030: Value restriction. Type inference has inferred the signature

val it : '_a

Either define 'it' as a simple data term, make it a function, or add a type constraint to instantiate the type parameters.

val list_head : 'a list -> 'a

*****

I kind of understand why it would return that error. I have even researched the error extensively on Google, but I have not been able discover a way to correct the definition of my function.

Can you please help? Thanks in advance for your time.