Earlier quoted context omitted.
This [1] might help 'get it' with regards to monads. Very easy to digest. You mention LINQ and the List abstraction. Yes IEnumerable is a monad (LINQ isn't in itself - it [the grammar] is the equivalent of 'do' notation in Haskell). Monads are simply 'wrapper types' that follow a couple of rules: 1. You must be able to construct one from the un-wrapped value (return in Haskell, new List (...) in C#) 2. It must implem…
Thanks for taking the time to write all that up. I think (too early to say) that seeing all this expressed in C#/Java(script)/Ruby/Python syntax is key for someone like me. I learned LINQ/Select(Many) and later all the map/filter/reduce functional goodness by playing with Clojure and never had a problem and never heard the word "monad" and was fine, totally fine. Later watching a video on Rx (MS's reactive extensions…
public class Option
{
public readonly bool HasValue;
public readonly T Value;
internal Option(bool hasValue, T value)
{
HasValue = hasValue;
Value = value;
}
public Option Select(Func map) =>
HasValue
? Option.Some(map(Value))
: Option.None();
public Option SelectMany(Func> bind, Func project) =>
HasValue
? bind(Value).Select(u => project(Value,u))
: Option.None();
}
public static class Option
{
public static Option Some(T value) =>
new Option(true, value);
public static Option None() =>
new Option(false, default(T));
}
public Option SelectMany(Func> bind, Func project)
{
if (HasValue)
{
var u = bind(Value);
if (u.HasValue)
{
return Option.Some(project(Value, u.Value));
}
else
{
return Option.None();
}
}
else
{
return Option.None();
}
}
The second static class: Option, contains the 'return' functions: Some or None. These wrap a value of type T in an Option.
Now if we use Option in a LINQ expression:
var option1 = Option.Some(10);
var option2 = Option.Some(10);
var none = Option.None();
var res1 = from x in option1
from y in option2
select x + y;
// res1.HasValue == true res1.Value == 20
var res2 = from x in option1
from y in none
select x + y;
// res2.HasValue == false
var res3 = from x in none
from y in option2
select x + y;
// res3.HasValue == false
do x var res = Option.None();
if( option1.HasValue )
{
if( option2.HasValue )
{
res = Option.Some(option1.Value + option2.Value);
}
}
Hopefully that clears the fog. I'll keep an eye on this thread for a few days, so feel free to drop any questions in here or on my project page.