[Haskell-beginners] firering event in netwire

Nathan Hüsken nathan.huesken at posteo.de
Sat Sep 29 19:19:46 CEST 2012

On 09/29/2012 08:56 AM, Ertugrul Söylemez wrote:
>> Or asked differently, how is the "keyDown" event defined, that was
>> talked of in an earlier mail?
> In the direct case you can define it as a simple composition:
>     isSym :: KeySym -> SDL.Event -> Bool
>     isSym s (KeyDown s') = s == s'
>     isSym _ _ = False
>     keyDown = require . isSym

While I understand the principals, I am unsure about the practical usage.
The input of keyDown is an SDL.Event. But in an application, I would
have a list of Events for every invocation of stepWire. So I could
define keyDown like this:

keyDown s = require . and . map (isSym s)

That would give me an event when my desired keypress event is in the
list of input events.
but if I then want to create a wire passed in this which outputs if a
given key is currently pressed, I would attempt something like this:

isPressed :: KeySym -> WireP [SDL.Event] Bool
isPressed s = hold . (True . (keyDown s) <|> False . (keyUp s))

But if some fast typer releases and presses within one stepWire a
certain key, isPressed would produce an incorrect result.


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