A program to test the factorial function

Version 1

This program illustrates how data is communicated between different parts of a Fudget program. It illustrates a simple way to combine application specific code (in this case the factorial function) with GUI elements from the Fudget library.

The program shows a numeric entry field at the bottom and a number display at the top. Whenever the user enters a number in the entry field and presses Return the factorial of that number is computed and displayed in the number display.

Here is the source code:

import Fudgets

main = fudlogue (shellF "Fac" facF)

facF = intDispF >==< mapF fac >==< intInputF

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

Things to note

• The program (facF) is structured as a serial composition of three parts, using the operator >==<, Notice that data flow from right to left. The parts are:
  • the numeric entry field intInputF,
  • mapF fac, an abstract fudget that applies fac, the factorial function, to integers received from the entry field, and
  • the number display intDispF which displays the factorials.
• We have used fudlogue and shellF on the top level as in the previous examples.