Getting input into Netwire programs

Question

I\'m getting started with Netwire version 5.

I have no problem writing all the wires I want to transform my inputs into my outputs.

Now the time has come to writ

Answer 1

The simplest way to put data into a Wire s e m a b is via the input a. It's possible, through the use of WPure or WGen to get data out of the state delta s or the underlying Monad m, but these take us further away from the main abstractions. The main abstractions are Arrow and Category, which only know about a b, and not about s e m.

Here's an example of a very simple program, providing input as the input a. double is the outermost wire of the program. repl is a small read-eval-print loop that calls stepWire to run the wire.

import FRP.Netwire
import Control.Wire.Core

import Prelude hiding (id, (.))

double :: Arrow a => a [x] [x]
double = arr (\xs -> xs ++ xs)

repl :: Wire (Timed Int ()) e IO String String -> IO ()
repl w = do
    a <- getLine
    (eb, w') <- stepWire w (Timed 1 ()) (Right a)
    putStrLn . either (const "Inhibited") id $ eb
    repl w'

main = repl double

Notice that we pass in the time difference to stepWire, not the total elapsed time. We can check that this is the correct thing to do by running a different top-level wire.

timeString :: (HasTime t s, Show t, Monad m) => Wire s e m a String
timeString = arr show . time

main = repl timeString 

Which has the desired output:

a
1
b
2
c
3