Factorial in A++

Example for versions A++ Interpreter

The first expression loads init library which contains all main language constructs (loops, conditional jumps, comparisons etc.). All of them are not included in language core but instead are defined via a limited set of primitives; thus, for example, if construct is defined as follows:: 

(define true   (lambda (x y) 
               x))
(define false  (lambda (x y) 
               y))
(define if     (lambda (b t f) 
               (b t f)))

The second example defines factorial as a recursive function. Note that the language standard defines two kinds of numbers — regular integers with typical arithmetical operations on them and “nominal” zero, one, two, ..., ten with specific operations. Numbers of different types can’t be decoded one into another and are to be used separately; in this case we use regular integers.

The third expression is the main loop, and the fourth one just calls it. print command ends the output with line feed, so overall program output looks as follows: 

-->0
-->! = 
-->1
-->1
-->! = 
-->1
-->2
-->! = 
-->2
-->3
-->! = 
-->6
-->4
-->! = 
-->24
-->5
-->! = 
-->120
...

Factorial values are calculated correctly up to 12!, after that they overflow and are printed as -1. 

(load "app/init.app")

(define factorial (lambda(n)
  (if (equal n 0)
    1
    (* n (factorial (- n 1))))))

(define main
  (lambda(n)
    (while (not (equal n 17))
      (lambda()
        (print n)
        (print "! = ")
        (print (factorial n))
        (define n (+ n 1))))))

(main 0)