A program to test the factorial function

Version 2, with improved layout

This program shows how to use layout combinators to improve the visual appearance of a Fudget program.

We have made the previous Factorial function example more self documenting by adding labels to the entry field and the output display. We have also changed the order of the two parts: the entry field is now above the display.

Here is the source code:

import Fudgets

main = fudlogue (shellF "Fac" facF)

facF = placerF (revP verticalP) (
        ("x! =" `labLeftOfF` intDispF) >==<
        mapF fac >==<
        ("x =" `labLeftOfF` intInputF))

fac 0 = 1
fac n = n * fac (n-1)

Things to note

• We have used the function labLeftOfF to put labels to the left of the entry field and the display. (In Haskell, back quotes can be used to turn any function into an infix operator, as we have done with labLeftOfF here)
• The function placerF can be applied to a composition of fudgets to specify the relative placement of the parts. (The layout system automatically picks some placement if you don't specify it yourself.) The first argument to placerF is a placer, in our case revP verticalP, where verticalP causes the parts to be stacked vertically with the leftmost fudget in the composition at the top, and revP reverses the order of the parts.
• Everything else is as in the previous examples.