I don't want to be just the person in computerphile who does all the history and nothing but history I'd actually like to do some programming with you and some of you in the comments what she said why don't you do Java or teach us some C or something and I thought no I've got a very good opportunity here to lead off from the PostScript story that's I've been telling and actually do some PostScript programming with you it's pretty easy to get software both for Linux for Mac and for PC that will enable you to run of the programs as I develop with you and even create ones of your own and I think that's important it's no use me getting into some language where the support is utterly minimal PostScript was invented ass Adobe by John Warnock and a team of co helpers it built on work that he'd done several years earlier when he worked with the Evans & Sutherland graphics company I think he'd done some more work on it's in a language called Jam when he was at Xerox PARC the M in Jam standing for John John and Martin that's right M is for Martin Newell anyway it became fully fledged when it got to Adobe it's a very big language it's got something like NUMBER_TOKEN operators in all but I think I've already said and let me emphasize again it's far more than a two-dimensional graphics language it is a full-blown programming language it can do anything as any other language can do it can do anything that the Turing machine can do and for that reason it's called a Turing complete language we're going to print out six instances of the text computer file first of all I'm going to do it with if you like a proper conventional PostScript program and no surprises in guessing that it will involve a for loop that goes around six times it's vital that you know something about PostScript and how it works first of all it's an interpreted language many of you will know what that means it means it's things like Perl Python JavaScript for the older generation among you it's things like lists what it means if you have an interpreted language is you look at what has been requested in the program and you do it there and then that way you gain great flexibility it doesn't necessarily run all that fast that's the real challenge it's in the very nature of PostScript that it uses a notation called post fix and that in turn relies for its execution environment on this notion of a stack we may be in a position to put this out as a separate film in its own right this is postfix I think his name is pronounced on and like Yanukovych people being unable to pronounce his name correctly and getting all the stresses and accents wrong decided that rather than pronouncing what they found hard they would call this polish notation now actually polish notation applies to using anything that isn't in fix I've seen prefix notation being called forward polish notation I've seen postfix giving its traditional name of reverse polish notation the stack is last in first out storage the last thing I put on the stack I pushed it on was this little white one the only thing I can directly get at at the top of the stack is the same thing so it's the last thing in and it's the first thing off and the act of taking it off the stack is called popping the stack so we'll
NO_SEGMENT_TOKEN