[Haskell-cafe] Help understanding this type

Zemyla zemyla at gmail.com
Tue Nov 6 16:40:18 UTC 2018


The type on "Ptr" doesn't actually affect what's inside; it's a convenience
for programmers. The functions that do things with XEvents just read bytes
from the Ptr's location.

On Tue, Nov 6, 2018, 10:36 Guru Devanla <gurudev.devanla at gmail.com wrote:

> Hello Haskell-Cafe,
>
> I have been recently studying the XMonad code and some related types
> available in the X11 bindings library.
>
> I came across this type:
>
> newtype XEvent = XEvent XEventPtr
>
> type XEventPtr = Ptr
> <http://hackage.haskell.org/package/base-4.10.1.0/docs/Foreign-Ptr.html#t:Ptr>
> XEvent
> <http://hackage.haskell.org/package/X11-1.9/docs/Graphics-X11-Xlib-Event.html#t:XEvent>
>
> Available here:
>
> http://hackage.haskell.org/package/X11-1.9/docs/Graphics-X11-Xlib-Event.html#t:XEvent
>
> It seems that this type is circular here. how does one use this type? Is
> it possible to create a value out of this type? What is the use of this
> type?
>
> Please could someone help me wrap my head around this?
>
> Thanks
>
>
>
>
>
>
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