trying to follow example in the expert f# book, and having an issue with the workflows...the code is as follows:
type Attempt<'a> = option<'a>
let succeed x = Some (x)
let fail = None
let bind p rest =
match p with
| None -> fail
| Some r -> rest r
let delay f = f()
type AttemptBuilder() =
member b.Return (x) = succeed x
member b.Bind (p, rest) = bind p rest
member b.Delay (f) = delay f
member b.Let (p, rest):Attempt<'a> = rest p //'
member b.ReturnFrom x = x
// using it:
let attempt = new AttemptBuilder()
let test foo =
attempt {
if not foo then return! fail else return foo
}
let check () =
attempt {
let! n1 = test true
let! n2 = test false
let! n3 = test true
let foo = n1,n2,n3
return foo
}
let foo = check ()
problem is , when all values are true, i get as expected, a Some(true, true, true), but if one of the values passed in is false, foo is null (!). Anyone ftw?
thanks!