to_string(obj)
Return a string representation of obj.
To_string is a generic function by default and can be overridden for custom data types without
an explicit declare generic.
string_append(to_string([1, 2, 3]), "123")
// [1, 2, 3]123
function point(x, y)
^(message)
| 'to_string -> ^() string_append(number_to_string(x), "@", number_to_string(y))
let p = point(10, 20)
to_string(p)
// 10@20