Re: [Haskell-beginners] netwire accum delayed by one

Nathan Hüsken wrote:

With this netwire based program:

mainWire = proc _ -> do accum (+) 0 -< 1

[...]

I get (output):

Right 0.0 Right 1.0 Right 2.0 ...

Should the output not start with 1.0 (and not 0.0)? The accum should be applied already in the first invocation, should it not?

Accum is documented to behave like a left scan, which also starts with the initial value. The reason is that for most applications you want the data dependency on the previous instant instead of on the current. Many useful FRP constructs can be (and are) expressed in terms of accum and accumT. Greets, Ertugrul -- Not to be or to be and (not to be or to be and (not to be or to be and (not to be or to be and ... that is the list monad.