David Sankel wrote:
Ahh, I thought you wanted to create widgets based on the String parameter.
No; that wasn't the intention. Although Windows *does* refer to window classes by name; I'm not sure if that's relevant here, though.
So in the following code, you would get an ambiguity error, right?
do -- mainWindow defined above a <- create "Some_Button" mainWindow [ label := "Okay" ] runGUI mainWindow -- or whatever it is.
Yes.
The system does not know if a is a button, a label, or whatever. It would have to look like this to remove the ambiguity
With a type-class approach, the type would need to be explicitly specified somewhere most of the time; it may be that you specify the variable's type, or you store the handle in a record field which has a defined type. Occasionally you might pass the handle to a function which only operates upon a certain type of widget, in which case the compiler could infer the type.
do -- mainWindow defined above a <- create "Some_Button" mainWindow [ label := "Okay" ] :: Button runGUI mainWindow -- or whatever it is.
It seems like this would defeat the purpose of having a generic create function since Button needs to be in there somewhere. Although, I do find your argument very credible.
Different types of widget seem to have enough in common that type
classes might be an appropriate solution. Other factors might
contradict this, though.
--
Glynn Clements