Func constructor
Implementation
Func(this.fun, this.argsCount) : super(null, null) {
List vrs = [];
List vrids = [];
for (int i = 0; i < argsCount; i++) {
vrs.add(Var(Func.nextId));
vrids.add(Func.nextId);
Func.nextId++;
}
this.args = [MakeArray(vrids), _expr(Function.apply(fun, vrs))];
}