[Haskell] Create a List

[Daan Leijen]

Hi Jose,

Jose manuel Hernando Cobeña wrote:

> 
> -hello, I need to create a list of Colors, and I like do this:
> 
> 
> list_colors <- varGet vColors
> ....
> color_red  <- checkBox p [text := "Red",  checked := False, on command 
> := do aux red list_colors ]
> ....
> where
>    aux one_color list_colors =
>      if (elem one_color list_colors)
>      then do
>         varSet vColors (delete one_color list_colors)
>      else do
>         varSet vColors (red:list_colors)
> 
> but the variable vColors no change and I can not create de list of colors.

You should pass the variable to the helper function -- not its value.
ie. this should work better:

...
colorRed <- checkBox p [text := "Red", on command := onRed red vColors]
...
where
   onRed color vColors
     = vColors [value :~ \colors -> if (color `elem` colors)
                                     then .. else color:colors]

I hope this helps,
  -- Daan.

ps. It is better to send wxHaskell related questions to
the wxhaskell-users at lists.sourceforge.net mailing list
instead of the Haskell list.

> 
> Thanks
> 
> 
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