Monad. ST. Internal
ST is concerned with restricted mutation. Mutation is restricted to a
region of mutable references. This kind is inhabited by phantom types
which represent regions in the type system.
ST type constructor allows local mutation, i.e. mutation which
does not "escape" into the surrounding computation.
ST computation is parameterized by a phantom type which is used to
restrict the set of reference cells it is allowed to access.
run function can be used to run a computation in the
Note: the type of
run uses a rank-2 type to constrain the phantom
h, such that the computation must not leak any mutable references
to the surrounding computation. It may cause problems to apply this
function using the
$ operator. The recommended approach is to use