Function from alpha to int

Asked Nov 08 '15 at 17:21

Active Nov 08 '15 at 17:36

Viewed 69 times

So i have a function that i'm trying to write:

fn (x:'a) => ???
(type: 'a -> int)

I've tried doing this:

fn (x:'a) => (x:int)

But obviously that returns a match constraint error. So is there any way I could go about doing this?

=== EDIT ===

Is there any way of 'reversing' the function? By this i mean having a function of type:

int -> 'a

edited Nov 08 '15 at 17:36

asked Nov 08 '15 at 17:21

madcrazydrumma

Just return any integer of your choice. – Aadit M Shah Nov 08 '15 at 17:23
@AaditMShah is there a way to reverse the function? Like go from int to 'a? – madcrazydrumma Nov 08 '15 at 17:29
Yes, there is. Either go into an infinite loop or throw an error. – Aadit M Shah Nov 08 '15 at 17:57
@AaditMShah how exactly would I do this without using exceptions? – madcrazydrumma Nov 08 '15 at 18:59
The function `fun f (x : int) = f x` has the type `f : int -> 'a` and the function `fun g x = 0` has the type `g : 'a -> int`. – Aadit M Shah Nov 08 '15 at 19:11
Is there a way to return a tuple of alphas? When i try `fun f (x:int) = (f x, f x);` it gives me a circularity error – madcrazydrumma Nov 08 '15 at 19:15
Yes, first define `fun f (x : int) = f x` and then define `fun g (x : int) = (f x, f x)`. However, I don't understand why you want a tuple of undefined values. What are you actually trying to do? – Aadit M Shah Nov 08 '15 at 19:20
Its for an assignment, I tried what you suggested before but it gives you the type `int -> 'a * 'b` and not `'a * 'a` – madcrazydrumma Nov 08 '15 at 19:22
1

Try `fun g (x : int) = let val y = f x in (y, y)`. – Aadit M Shah Nov 08 '15 at 19:29

0 Answers0