How do I access a random member of a Tuple?

I would like to access a random member of a tuple and I'm not sure how to set #n to a variable.

Here is my code:

val lis = ("a","b","c","d")
val randNumber = Random.randRange (1,4) (Random.rand (0,1)) 
val randChar = #randNumber lis //this is where its failing

This is how I would normally access, say member #2:

val lis = ("a","b","c","d")
val ranChar = #2 lis;

So my question is how do I set #2 to a variable in the example above??

Thank you very muc开发者_运维技巧h in advance!!

There are some workarounds, for example, you can explicitly match randNumber and call appropriate member functions:

    val randChar = case randNumber of
                      1 => #1 lis
                    | 2 => #2 lis
                    | 3 => #3 lis
                    | _ => #4 lis

Of course, this one doesn't scale very well. Another workaround is changing representation of lis to List and use List.nth:

List.nth(lis, randNumber-1)

Hope it helps you somehow.

I suppose you cannot. What would be the type of the access operator? If you want dynamic random access to your data, you should convert it into a vector first.

PS: there are languages (Coq, Agda, etc.) where such access operator can be typed, but that would require dependent types (or at least type-level integers plus some magic, maybe Omega can also do that).