An Up/Down/Reset Counter

This example shows how to create parallel compositions of many fudgets of the same type.

This program extends the counter example with yet another button. You can now increment, decrement and reset the counter.

Here is the source code:

import Fudgets

main = fudlogue (shellF "Up/Down/Reset Counter" counterF)

counterF = intDispF >==< mapstateF count 0 >==< buttonsF

data Buttons = Up | Down | Reset  deriving (Eq)

buttonsF = listF [(Up,buttonF "Up"),
                  (Down,buttonF "Down"),
                  (Reset,buttonF "Reset")]

count n (Up,Click) = (n+1,[n+1])
count n (Down,Click) = (n-1,[n-1])
count n (Reset,Click) = (0,[0])

Things to note

• When putting more than two fudgets of the same type in parallel, it is more convenient to use listF than >+<. The argument to listF is a list of pairs of adresses and fudgets. The adresses are then used when you send messages to and receive messages from the components in the composition.
• In this program there is a user defined enumeration type Buttons, the elements of which are used as the adresses of the buttons. The messages received by the count function are pairs of Button values and Clicks.
• Everything else is as in the previous example.