funcs that generate funcs that generate values. and things yield returning as enumerables

generation.cs

static public class FunFactory
{
    static public Func<TResult> Make<TResult>(TResult a, Func<TResult, TResult> step)
    {
        TResult next=a;
        return ()=>{ TResult cur=next; next=step(cur); return cur; };
    }
    
    static public Func<TResult> Cycle<TResult>(IEnumerable<TResult> values) 
    { 
        IEnumerator<TResult> it=values.GetEnumerator();
        return ()=>{ if(it.MoveNext() || (it=values.GetEnumerator()).MoveNext())
                         return it.Current;
                     throw new System.InvalidOperationException("No next value");};
    }

    static public Func<TResult> Cycle<TResult>(TResult[] values)
    {
        int idx=-1;
        return ()=>values[(idx = ++idx%values.Length)];
    }

    static public Func<char> Cycle(char from, char to) { int n=from-1; return ()=>(char)(n=(++n>to)?from:n); }
    static public Func<int>  Cycle(int  from,  int to) { int n=from-1; return ()=>      (n=(++n>to)?from:n); }
}

static public class Sequence
{
    public static IEnumerable<TResult> Generate<TResult>(TResult start, Func<TResult,TResult> step)
    {
        for(TResult current = start; true; current = step(current))
            yield return current;
    }

    public static IEnumerable<TResult> Generate<TSeed, TResult>(TSeed start, Func<TSeed,TSeed> step, Func<TSeed,TResult> convert)
    {
        for(TSeed current = start; true; current = step(current))
            yield return convert(current);
    }

    public static IEnumerable<char> Cycle(char a, char b)
    {
        return Generate(a, (c => (char)(++c>b ? a : c)));
    }
}