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

Hi David, I was referring to the `f' in the `runAuto' function, not the `liftAu' function. -db On Wed, Oct 19, 2011 at 8:53 PM, David Barbour wrote:

On Wed, Oct 19, 2011 at 8:07 PM, Captain Freako wrote:

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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

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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?