f# - Why can't I Seq.take more than 5 values? -

whilst trying understand seq.unfold, have been playing following f# produces sequence of triangle numbers...

let tri_seq =    1.0    |> seq.unfold (fun x -> (0.5 * x * (x + 1.0), x + 1.0))    |> seq.map (fun n -> int n) 

this seems work fine, in can following...

tri_seq |> seq.nth 10 

...and shows right number, whatever value pass it.

now, i'm trying print out first (say) ten values in sequence, rather above code gets nth. tried following...

tri_seq |> seq.take 10 |> seq.map (fun n -> printfn "%d" n) 

...but prints first 5 values. whatever use value passed seq.take, ever maximum of 5 results, though when using seq.nth, can go far like.

anyone able explain me? why can't past fifth value?

the problem you're using seq.map print values. sequences lazy , resulting sequence never evaluated - see 5 values because f# interactive prints first 5 elements of sequence.

you can use seq.iter iterates on whole sequence:

tri_seq |> seq.take 10 |> seq.iter (fun n -> printfn "%d" n) 

the key difference seq.map returns new sequence values produced function specify while seq.iter not return , iterates on input.

in case, can use partial function application , make code bit shorter:

tri_seq |> seq.take 10 |> seq.iter (printfn "%d")