1 Imparative Features ML supports references and assignments. References are a type-safe form of pointer to the heap.
Assignment provides a way to change the object to which the pointer refers.
The type t ref is the type of references to values of type t . To solve this problem a reference has a non-generalizable type. Within a module, it takes the narrowest type possible. When one write file A.sml , he should also write A.sig . The sig file contains an interface , while the sml file contains the implementation.