applay for template function with sumtypes result?

[kiriakov]

Hi. I can't handle template. It all looks sad, build ok, test 
error.

```
struct ParsResult(T) { T[] _in; T[] _out; }
struct Err(T) { T[] x; }

struct Result(T) {
     SumType!(ParsResult!T, Err!T) data;
     alias data this;
     this(Value)(Value value) { data = value; }	
}


Result!T applay(T)(Result!T function (T[]) pure fun, T[] x) pure 
{ return fun(x); }
ParsResult!char f (char[] x) pure { return 
ParsResult!char(x[1..$], x[2..$]); }

unittest
{
     writeln(applay(&f,"String10".dup));
}
```

I got

Error: none of the overloads of template `mexception.pars` are 
callable using argument types `!()(ParsResult!char 
delegate(char[] x) pure nothrow @nogc @safe, char[])`
source/mexception.d(64,10):        Candidate is: 
`pars(T)(Result!T function(T[]) pure fun, T[] x)`