How to pass values down the pipe sequence?

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1 
renderList2 : List Int -> Int -> Html msg
renderList2 lst limit =
  let 
    attrBool x = if x > limit then True else False 
  in 
    lst
        |> List.map (\i -> (String.fromInt i ++ ", "))
        |> List.map (span [classList [("numberRed", True)] ] << List.singleton << text)
        |> ul []

How do I pass the value of i to attrBool x so that the attrBool is True only when i > limit?

2

In this case, you can do a single List.map for the transformation to a string and the transformation to a span. If you do these two operations in the same function, then you keep access to i.
Here is what I mean in code:

renderList2 : List Int -> Int -> Html msg
renderList2 lst limit =
  let 
    attrBool x = if x > limit then True else False 
  in 
    lst
        |> List.map (\i -> span [classList [("numberRed", attrBool i)] ] [ text (String.fromInt i ++ ", ")])
        |> ul []
1 Like
3

You may know, but a tip if that is not the case… the if statement can also be done inline:

renderList2 : List Int -> Int -> Html msg
renderList2 lst limit =
    lst
        |> List.map (\i -> span [classList [("numberRed", i > limit )] ] [ text (String.fromInt i ++ ", ")])
        |> ul []
1 Like
4

Yes, thanks for that tip. I used it.

5

But what if I want the value i to propagate down the pipeline, is it even possible?

6

It is possible, but you would have to be explicit about it. Basically, at every step of the pipeline, you’d return something (like a tuple), that contains i and the value you actually want to work on. Here is an example using a tuple:

renderList2 : List Int -> Int -> Html msg
renderList2 lst limit =
  let 
    attrBool x = if x > limit then True else False 
  in 
    lst
        |> List.map (\i -> (i, String.fromInt i ++ ", ")) -- Return a tuple
        |> List.map (\(i, intAsText) -> -- Deconstructing the tuple
            span [classList [("numberRed", attrBool i)] ] [text intAsText]
        )
        |> ul []
1 Like
7

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