I have an Ocaml function that is giving me errors.
What I am trying to do:
Recursively create a List of random numbers (0-2) of size "limit".
Here's what I have:
let rec carDoorNumbers = fun limit ->
match limit with
| [1] -> Random.int 3
| [] -> Random.int 3 :: carDoorNumbers (limit-1);;
I am getting this error:
Error: This expression has type 'a list
but an expression was expected of type int
Think about what your function has to do: given a limit, you have to create a list of numbers. So your type is something like carDoorNumbers : int -> int list.
Looking at that, it seems you have two errors. First, you're matching limit (which should be an int) against a list pattern. [1] -> ... matches a list containing only the element 1 and [] matches the empty list; you really want to match against the number 1 and any other number n.
The second error is that you return two different types in your match statement. Remember that you are supposed to be returning a list. In the first case, you are returning Random.int 3, which is an int rather than an int list. What you really want to return here is something like [Random.int 3].
The error you got is a little confusing. Since the first thing you returned was an int, it expects your second thing to also be an int. However, your second case was actually correct: you do return an int list! However, the compiler does not know what you meant, so its error is backwards; rather than changing the int list to an int, you need to change the int to an int list.
n, which matches anything and binds it to the variable n. (You can naturally name the variable whatever you want.)Your match expression treats limit like a list. Both [1] and [] are lists. That's what the compiler is telling you. But it seems limit should be an integer.
To match an integer, just use an integer constant. No square brackets.
(As a side comment, you might want to be sure the function works well when you pass it 0.)
_, which will work for this code. There's no harm at all in using if/then/else in OCaml. That's what I usually use for ints.