Here we give an example of using the object-oriented features in Camelot. The code
below, together with the two standard utility functions **rev** and
**len** for list reversal and length, defines a program for Sun's MIDP
platform (as described in midp), which runs on devices such as PalmOS PDAs.
The program displays the list of primes in an interval. Two numbers are entered into
the first page of the GUI, and when a button is pressed a second screen appears with
the list of primes, calculated using the sieve of Eratosthenes, along with a button
leading back to the initial display.

This example has been compiled with our current compiler implementation, and executed on a PalmOS device.

class primes = javax.microedition.midlet.MIDlet with implement javax.microedition.lcdui.CommandListener field exitCommand: javax.microedition.lcdui.Command field goCommand: javax.microedition.lcdui.Command field doneCommand: javax.microedition.lcdui.Command field mainForm: javax.microedition.lcdui.Form (* lower and upper limits: *) field lltf: javax.microedition.lcdui.TextField field ultf: javax.microedition.lcdui.TextField field display: javax.microedition.lcdui.Display maker () = let _ = display <- (javax.microedition.lcdui.Display.getDisplay (this:> javax.microedition.midlet.MIDlet)) in let _ = goCommand <- (new javax.microedition.lcdui.Command "Go" javax.microedition.lcdui.Command.SCREEN 1) in let _ = exitCommand <- (new javax.microedition.lcdui.Command "Exit" javax.microedition.lcdui.Command.SCREEN 2) in let t = new javax.microedition.lcdui.Form "Primes" in let ll = new javax.microedition.lcdui.TextField "Lower limit:" "" 10 javax.microedition.lcdui.TextField.NUMERIC in let _ = lltf <- ll in let _ = t#append ll in let ul = new javax.microedition.lcdui.TextField "Upper limit:" "" 10 javax.microedition.lcdui.TextField.NUMERIC in let _ = ultf <- ul in let _ = t#append ul in let _ = t#addCommand (this#goCommand) in let _ = t#addCommand (this#exitCommand) in let _ = mainForm <- t in t#setCommandListener this method startApp (): unit = this#display#setCurrent (this#mainForm) method pauseApp (): unit = () method destroyApp (b:bool): unit = () method commandAction (cmd: javax.microedition.lcdui.Command) (s: javax.microedition.lcdui.Displayable) : unit = if cmd#equals (this#exitCommand) then let _ = this#destroyApp false in this#notifyDestroyed () (* create & display list of primes *) else if cmd#equals (this#goCommand) then let lower_limit = int_of_string (this#lltf#getString()) in let upper_limit = int_of_string (this#ultf#getString()) in let primes = new javax.microedition.lcdui.Form "Primes" in let _ = appendPrimes lower_limit upper_limit primes in let done = new javax.microedition.lcdui.Command "Done" javax.microedition.lcdui.Command.SCREEN 1 in let _ = doneCommand <- done in let _ = primes#addCommand done in let _ = primes#setCommandListener this in let _ = javax.microedition.lcdui.AlertType.INFO#playSound (this#display) in this#display#setCurrent primes (* back to main form *) else if cmd#equals (this#doneCommand) then this#display#setCurrent (this#mainForm) else () end (* Generate a list of prime numbers in an interval [a..b] *) (* Integer square roots *) let increase k n = if (k+1)*(k+1) > n then k else k+1 let rec intsqrt n = if n = 0 then 0 else increase (2*(intsqrt (n/4))) n (* n is divisible by no member of l which is <= sqrt n *) let isPrime n l lim = match l with [] -> true | h::t -> h <= lim && n mod h <> 0 && isPrime n t lim (* generate list of primes between n and top *) let make1 n top acc = if n > top then rev acc [] else if isPrime n acc n then make1 (n+2) top (n::acc) else make1 (n+2) top acc let makeSmallPrimes top = make1 3 top [2] let makePrimes n top smallPrimes = if n > top then [] else if isPrime n smallPrimes n then n::(makePrimes (n+2) top smallPrimes) else makePrimes (n+2) top smallPrimes let appList l (f: javax.microedition.lcdui.Form) = match l with [] -> () | (h::t)@_ -> let _ = f#append ( (string_of_int h)^"\n") in appList t f let appendPrimes bot top (f: javax.microedition.lcdui.Form) = let smallPrimes = makeSmallPrimes (intsqrt top) in let primes = makePrimes (bot + 1 - bot mod 2) top smallPrimes in let s = (string_of_int (len primes)) ^ " primes\n" in let _ = f#append s in appList primes f |