Question

I can define a simple list in F# as follows and iterate over it with the following code:

let ar = [0;1;2;3]
ar |> Seq.iter (fun x -> printfn "Ar: %A" x)

Now consider a nested sequence as follows:

let ar1 = [1;2;3;4]
let ar2 = [5;6;7;8]
let nested_array = [ar1; ar2]

How can I Iterate over this – the following code below gets an error:

‘Unexpected infix operator in lambda expression’

What I’m trying to do here is to iterate over the outer sequence and pipe that forward to a second iterator which then lets me access the contents of the inner arrays.

nested_array |>
Seq.iter (fun x -> |> 
                    Seq.iter  (fun y ->
                    printfn "Ar: %A" y))

What am I missing here – I suspect a syntax problem or (more serious/likely) a lack of F#/FP comprehension .

Answer 1

You’re not using your variable x. Try either

nested_array |> Seq.iter (fun x -> x |> Seq.iter (fun y -> printfn "Ar: %A" y))

or (eliminating the use of x entirely)

nested_array |> Seq.iter (Seq.iter (fun y -> printfn "Ar: %A" y))

or even (eliminating y as well)

nested_array |> Seq.iter (Seq.iter (printfn "Ar: %A"))