Example
Values can be given names using let:
# let a = 1;;
val a : int = 1
You can use similar syntax to define a function. Just provide additional parameters for the arguments.
# let add arg1 arg2 = arg1 + arg2;;
val add : int -> int -> int = <fun>
We can call it like this:
# add 1 2;;
- : int = 3
We can pass values in directly like that, or we can pass values bound to names:
# add a 2;;
- : int = 3
The line that the interpreter gives us after we define something is the value of the object with its type signature. When we gave it a simple value bound to a, it came back with:
val a : int = 1
Which means a is an int, and its value is 1.
The type signature of our function is a little more complicated:
val add : int -> int -> int = <fun>
The type signature of add looks like a bunch of ints and arrows. This is because a function that takes two arguments is actually a function which just takes one argument, but returns another function that takes the next argument. You could instead read it like this:
val add : int -> (int -> int) = <fun>
This is useful when we want to create different sorts of functions on the fly. For example, a function that adds 5 to everything:
# let add_five = add 5;;
val add_five : int -> int = <fun>
# add_five 5;;
- : int = 10
# add_five 10;;
- : int = 15
