public static StateMonad <TState, IEnumerable <StateContentPair <TState, TContent> > > CreateStateMonadFunctionally <TState, TContent>(IEnumerable <TContent> list, StateMonad <TState, TState> updateMonad)
{
var monad = list
.Aggregate(StateMonad.Return <TState, IEnumerable <StateContentPair <TState, TContent> > >(new List <StateContentPair <TState, TContent> >()), (current, s) => current
.Bind(x1 => updateMonad
.Bind(x => StateMonad.Return <TState, IEnumerable <StateContentPair <TState, TContent> > >(new[] { StateContentPair.Create(x, s) }))
.Bind(x2 => StateMonad.Return <TState, IEnumerable <StateContentPair <TState, TContent> > >(x1.Concat(x2)))));
return(monad);
}
private static StateMonad <TState, IEnumerable <StateContentPair <TState, TContent> > > CreateStateMonadRecursively <TState, TContent>(IReadOnlyCollection <TContent> list, StateMonad <TState, TState> updateMonad, StateMonad <TState, IEnumerable <StateContentPair <TState, TContent> > > result)
{
if (!list.Any())
{
return(result);
}
return(CreateStateMonadRecursively(list.Skip(1).ToList(), updateMonad, result
.Bind(res => updateMonad
.Bind(state => StateMonad.Return <TState, IEnumerable <StateContentPair <TState, TContent> > >(new[] { StateContentPair.Create(state, list.First()) }))
.Bind(nextItem => StateMonad.Return <TState, IEnumerable <StateContentPair <TState, TContent> > >(res.Concat(nextItem))))));
}
/**
* Simple example of running a string through a calculation involving
* destructive update modelled by a state monad.
*
* @param initial the starting string.
* @return the result of running the string through the computation.
*/
public static String ToUpperCase(String initial)
{
var m = new StateMonad();
// do a <- lookup
// mutate(a.toUpperCase)
// lookup
Computation c =
m.Bind(m.Lookup(),
new C(m));
return((String)m.Run(c, initial).Value());
}
private static StateMonad <TState, Tree <StateContentPair <TState, T> > > CreateLabeledTree <TState, T>(Tree <T> tree, StateMonad <TState, TState> updateMonad)
{
if (tree is Leaf <T> )
{
var leaf = (tree as Leaf <T>);
return(updateMonad.Bind(n => StateMonad.Return <TState, Tree <StateContentPair <TState, T> > >(Leaf.Create(StateContentPair.Create(n, leaf.Content)))));
}
if (tree is Branch <T> )
{
var branch = (tree as Branch <T>);
// recursion
return(CreateLabeledTree(branch.Left, updateMonad)
.Bind(newleft => CreateLabeledTree(branch.Right, updateMonad)
.Bind(newright => StateMonad.Return <TState, Tree <StateContentPair <TState, T> > >(Branch.Create(newleft, newright)))));
}
throw new Exception("MakeMonad/MLabel: impossible tree subtype");
}
