want "is" operator on nodes and constructors

[BertLisser]

Created 2010-03-24 by [email protected] assigned to [email protected]

rascal> data Bool = and(Bool l, Bool r) | or(Bool l, Bool r) |true() | false();
rascal> Bool b = and(true(),false());
rascal> b is and
bool: true
rascal> b is rue
bool: false

and of course, also the "isnot".

so: b is and <==> (and(,) := b)