module Foo use mach.int.Int63 let c = 1 end
results in not very informative typing error:
Cannot cast an integer literal to type 'xi.
I found it first in an example as the following, where the type
int63 is not even in the namespace of Foo. In this case, if you imagine a complex module, it's not easy to find the cause of the error.
module Bar use mach.int.Int63 end module Foo use Bar let c = 1 end