How can I interpret property based test code? - f#

Question

How can I interpret property based test code?
I'm struggling to translate the instructions on the following snippet:
let myProperty = Prop.forAll fiveAndThrees <| fun number ->
let actual = transform number
let expected = "jbdhjsdhjdsjhsdglsdjlljh"
expected = actual
Check.QuickThrowOnFailure myProperty
Specifically, I'm struggling with the backwards pipeline operator (i.e. "<|").
Here's the test:
[<Fact>]
let ``FizzBuzz.transform returns FizzBuzz`` () =
let fiveAndThrees = Arb.generate<int> |> Gen.map ((*) (3 * 5))
|> Arb.fromGen
let myProperty = Prop.forAll fiveAndThrees <| fun number ->
let actual = transform number
let expected = "jbdhjsdhjdsjhsdglsdjlljh"
expected = actual
Check.QuickThrowOnFailure myProperty
Can someone please guide me step by step on how this code works?
Could this be rewritten using the forward pipe operator (i.e. "|>")?

Answer 1

This answer only covers why <| is used instead of |>.
Here are 5 examples that work toward making use of <| with a large function. The 6th example is to show how the code looks using |> instead of <|. The point is that with the 6th example using |> you have to look into the code to find the primary function funThatNeedsListAndFunc but with <| the primary function funThatNeedsListAndFunc is obvious. So you typically see <| when the last parameter is a function and you want to pass in the function after the primary function for easier comprehension. That's all; don't read more into than that.
After reading the Mark's blog I also learned that <| is useful to remove ( ) around fun. An example using ( ) is given as example 7.
let funThatNeedsListAndFunc list func =
func list
let func = List.sum
let list = Seq.toList { 0 .. 5}
let result1 = funThatNeedsListAndFunc list func
printfn "result1: %A" result1
let result2 = funThatNeedsListAndFunc list <| func
printfn "result2: %A" result2
let result3 = funThatNeedsListAndFunc list <| List.sum
printfn "result3: %A" result3
let result4 = funThatNeedsListAndFunc list <|
fun (list : 'a list) -> List.sum list
printfn "result4: %A" result4
let result5 = funThatNeedsListAndFunc list <|
fun (list : 'a list) ->
// This will be a long function
let a = 1
let b = 2
let c = a * b
let result = List.sum list
let d = "more useless lines"
let (e,f,g) = ("a", 15, 3.0)
result
printfn "result5: %A" result5
.
let result6 =
fun (list : 'a list) ->
// This will be a long function
let a = 1
let b = 2
let c = a * b
let result = List.sum list
let d = "more useless lines"
let (e,f,g) = ("a", 15, 3.0)
result
|> funThatNeedsListAndFunc list
printfn "result6: %A" result6
.
let result7 =
funThatNeedsListAndFunc list (fun (list : 'a list) ->
// This will be a long function
let a = 1
let b = 2
let c = a * b
let result = List.sum list
let d = "more useless lines"
let (e,f,g) = ("a", 15, 3.0)
result)
printfn "result7: %A" result7