Initial data commit

Task/Arithmetic-Rational/Ol/arithmetic-rational.ol

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+(define x 3/7)
+(define y 9/11)
+(define z -2/5)
+
+; demonstrate builtin functions:
+
+(print "(abs " z ") = " (abs z))
+(print "- " z " = " (- z))
+(print x " + " y " = " (+ x y))
+(print x " - " y " = " (- x y))
+(print x " * " y " = " (* x y))
+(print x " / " y " = " (/ x y))
+(print x " < " y " = " (< x y))
+(print x " > " y " = " (> x y))
+
+; introduce new functions:
+
+(define (+:= x) (+ x 1))
+(define (-:= x) (- x 1))
+
+(print "+:= " z " = " (+:= z))
+(print "-:= " z " = " (-:= z))
+
+; finally, find all perfect numbers less than 2^15:
+
+(lfor-each (lambda (candidate)
+      (let ((sum (lfold (lambda (sum factor)
+                     (if (= 0 (modulo candidate factor))
+                        (+ sum (/ 1 factor) (/ factor candidate))
+                        sum))
+                  (/ 1 candidate)
+                  (liota 2 1 (+ (isqrt candidate) 1)))))
+         (if (= 1 (denominator sum))
+            (print candidate (if (eq? sum 1) ", perfect" "")))))
+   (liota 2 1 (expt 2 15)))