[Haskell-cafe] How to implement a digital filter, using Arrows?

David Barbour dmbarbour at gmail.com
Thu Oct 20 05:53:42 CEST 2011

On Wed, Oct 19, 2011 at 8:07 PM, Captain Freako <capn.freako at gmail.com>wrote:

> One more question on the `runAuto' code, John:
> If I understand the code correctly, `f' is an arrow. Yet, we're using
> it on the right side of `=' in a simple assignment. How are we getting
> away with that?
> Thanks,
> -db
> liftAu' f s0 = proc x -> do
>>    rec (y,s') <- arr f -< (x,s)
>>    s <- delay s0 -< s'
>>    returnA -< (y,s)
The value `f` is a function - a parameter of liftAu'. While all functions
are arrows (Arrow is defined on (->)), the value `arr f` is an arrow of the
automaton model. The `=` symbol is used to define the liftAu function. What
are you imagining?
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