public void Either_Binds()
{
Func<int, Either<string, int>> f = (x) => {
if (x < 0) {
return new Either.Left<string, int>("Cannot take sqrt of negative value");
}else{
return new Either.Right<string, int>((int) Math.Sqrt(x));
}
};
var r = new Either.Right<string, int> (4);
var res = r.Bind (f);
Assert.IsTrue (res is Either.Right<string, int>);
Assert.AreEqual ((res as Either.Right<string, int>).r, 2);
var l = new Either.Left<string, int> ("blah");
res = l.Bind (f);
Assert.IsTrue (res is Either.Left<string, int>);
Assert.AreEqual ((res as Either.Left<string, int>).l, "blah");
var r2 = new Either.Right<string, int> (-1);
res = r2.Bind (f);
Assert.IsTrue (res is Either.Left<string, int>);
Assert.AreSame ((res as Either.Left<string, int>).l, "Cannot take sqrt of negative value");
}
public void Either_Binds()
{
Func <int, Either <string, int> > f = (x) => {
if (x < 0)
{
return(new Either.Left <string, int>("Cannot take sqrt of negative value"));
}
else
{
return(new Either.Right <string, int>((int)Math.Sqrt(x)));
}
};
var r = new Either.Right <string, int> (4);
var res = r.Bind(f);
Assert.IsTrue(res is Either.Right <string, int>);
Assert.AreEqual((res as Either.Right <string, int>).r, 2);
var l = new Either.Left <string, int> ("blah");
res = l.Bind(f);
Assert.IsTrue(res is Either.Left <string, int>);
Assert.AreEqual((res as Either.Left <string, int>).l, "blah");
var r2 = new Either.Right <string, int> (-1);
res = r2.Bind(f);
Assert.IsTrue(res is Either.Left <string, int>);
Assert.AreSame((res as Either.Left <string, int>).l, "Cannot take sqrt of negative value");
}
public void Either_Maps()
{
Func<int, int> f = (x) => x + 3;
var r = new Either.Right<string, int> (4);
var res = r.FMap (f);
Assert.IsTrue (res is Either.Right<string, int>);
Assert.AreEqual ((res as Either.Right<string, int>).r, 7);
var l = new Either.Left<string, int> ("blah");
res = l.FMap (f);
Assert.IsTrue (res is Either.Left<string, int>);
}
public void Either_Maps()
{
Func <int, int> f = (x) => x + 3;
var r = new Either.Right <string, int> (4);
var res = r.FMap(f);
Assert.IsTrue(res is Either.Right <string, int>);
Assert.AreEqual((res as Either.Right <string, int>).r, 7);
var l = new Either.Left <string, int> ("blah");
res = l.FMap(f);
Assert.IsTrue(res is Either.Left <string, int>);
}
// 3. Write a function `Safely` of type ((() → R), (Exception → L)) → Either<L, R> that will
// run the given function in a `try/catch`, returning an appropriately
// populated `Either`.
// Safely : ((() -> R), (Exception -> L)) -> Either<L, R> ; see also solutions
private static Either <L, R> Safely <R, L>(Func <R> funcR, Func <Exception, L> funcL)
{
try
{
R r = funcR();
Either.Right <R> right = Right(r);
return(right); // here conversion to Either<L, R> is done through the operator overload conversion in Either<L, R>
}
catch (Exception e)
{
L l = funcL(e);
Either.Left <L> left = Left(l);
return(left); // here conversion to Either<L, R> is done through the operator overload conversion in Either<L, R>
}
}
