Add all the A tasks

Task/Abstract-type/Argile/abstract-type.argile

@@ -0,0 +1,38 @@
+use std
+
+(: abstract class :)
+
+class Abs
+   text		name
+   AbsIface	iface
+
+class AbsIface
+   function(Abs)(int)->int	method
+
+let Abs_Iface = Cdata AbsIface@ {.method = nil}
+
+.: new Abs :. -> Abs {let a = new(Abs); a.iface = Abs_Iface; a}
+
+=: <Abs self>.method <int i> := -> int
+   (self.iface.method is nil) ? 0 , (call self.iface.method with self i)
+
+(: implementation :)
+
+class Sub <- Abs { int value }
+
+let Sub_Iface = Cdata AbsIface@ {.method = (code of (nil the Sub).method 0)}
+
+.: new Sub (<int value = -1>) :. -> Sub
+   let s = new (Sub)
+   s.iface = Sub_Iface
+   s.value = value
+   s
+
+.: <Sub this>.method <int i> :. -> int {this.value + i}
+
+(: example use :)
+
+.:foobar<Abs a>:. {print a.method 12 ; del a}
+foobar (new Sub 34)	(: prints 46 :)
+foobar (new Sub)	(: prints 11 :)
+foobar (new Abs)	(: prints  0 :)