Again, I'm not sure what you are trying to achieve here. I just offered a funny piece of hackdom from thirty years ago but you seem to want to turn this into a language war?
-- Cédric On Tue, Oct 30, 2012 at 7:56 PM, Ricky Clarkson <ricky.clark...@gmail.com>wrote: > datatype 'a 'b either = > Left of 'a > | Right of 'b > > ML, 1973. Pascal is only 3 years older, but much much sillier. > > On Tue, Oct 30, 2012 at 11:39 PM, Cédric Beust ♔ <ced...@beust.com> wrote: > > I hope you're not suggesting that I was contrasting the quality of a > piece > > of code that's forty years old with one written in a modern programming > > language... > > > > -- > > Cédric > > > > > > > > > > On Tue, Oct 30, 2012 at 7:34 PM, Ricky Clarkson < > ricky.clark...@gmail.com> > > wrote: > >> > >> The difference being that your Pascal example has no notion of one > >> side being the real side, hence it being useful for subverting the > >> type system, and an Either has that defined and doesn't allow any > >> subversion, but lets you abstract over it being one thing or the > >> other. In C it can be used for 'evil' too but a common approach is to > >> have a tag saying what the type really is. > >> > >> On Tue, Oct 30, 2012 at 11:25 PM, Cédric Beust ♔ <ced...@beust.com> > wrote: > >> > Bouncing off another topic mentioned in the latest podcast: union > types. > >> > Yes, C had them but the first time I was exposed to them was in > Pascal, > >> > and > >> > the discussion on the podcast reminded me of an awesome hack that blew > >> > my > >> > mind a very long time ago. > >> > > >> > Pascal was well known to be very strict and safe. Among other things, > it > >> > didn't let you access the memory directly, which was a big deal in > the 8 > >> > bit > >> > era where memory protection was a distant dream and PEEK and POKE were > >> > how > >> > you wrote games. > >> > > >> > And then, one day, somebody found a way to address the memory using > >> > standard > >> > Pascal. Here is the trick (from memory, so it's probably not quite > >> > correct): > >> > > >> > type > >> > b = record > >> > x : array[1..65536] of ^integer; > >> > y : integer; > >> > end; > >> > > >> > This declares a union type that is made of either an array of 65k > >> > pointers > >> > to integers or a single integer. Then you initialize this record in > its > >> > "x" > >> > side with the memory address you want to peek and you access it by > using > >> > the > >> > "x" side of the record. > >> > > >> > It took me months to understand what this code did, but what a > >> > revelation it > >> > was when it finally clicked... > >> > > >> > By the way, these types are formally known as "sum types" (Either is > one > >> > of > >> > them). > >> > > >> > -- > >> > Cédric > >> > > >> > > >> > -- > >> > You received this message because you are subscribed to the Google > >> > Groups > >> > "Java Posse" group. > >> > To post to this group, send email to javaposse@googlegroups.com. > >> > To unsubscribe from this group, send email to > >> > javaposse+unsubscr...@googlegroups.com. > >> > For more options, visit this group at > >> > http://groups.google.com/group/javaposse?hl=en. > >> > >> -- > >> You received this message because you are subscribed to the Google > Groups > >> "Java Posse" group. > >> To post to this group, send email to javaposse@googlegroups.com. > >> To unsubscribe from this group, send email to > >> javaposse+unsubscr...@googlegroups.com. > >> For more options, visit this group at > >> http://groups.google.com/group/javaposse?hl=en. > >> > > > > -- > > You received this message because you are subscribed to the Google Groups > > "Java Posse" group. > > To post to this group, send email to javaposse@googlegroups.com. > > To unsubscribe from this group, send email to > > javaposse+unsubscr...@googlegroups.com. > > For more options, visit this group at > > http://groups.google.com/group/javaposse?hl=en. > > -- > You received this message because you are subscribed to the Google Groups > "Java Posse" group. > To post to this group, send email to javaposse@googlegroups.com. > To unsubscribe from this group, send email to > javaposse+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/javaposse?hl=en. > > -- You received this message because you are subscribed to the Google Groups "Java Posse" group. To post to this group, send email to javaposse@googlegroups.com. To unsubscribe from this group, send email to javaposse+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/javaposse?hl=en.
