Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!caen!uwm.edu!ux1.cso.uiuc.edu!midway!midway!stephen From: stephen@estragon.uchicago.edu (Stephen P Spackman) Newsgroups: comp.lang.misc Subject: Re: A Hard Problem for Static Type Systems Message-ID: Date: 3 May 91 11:12:50 GMT References: <2392@optima.cs.arizona.edu> <3156@opal.cs.tu-berlin.de> <51984@nigel.ee.udel.edu> Sender: news@midway.uchicago.edu (NewsMistress) Organization: University of Chicago CILS Lines: 44 In-Reply-To: new@ee.udel.edu's message of 26 Apr 91 22: 13:16 GMT In article <51984@nigel.ee.udel.edu> new@ee.udel.edu (Darren New) writes: |Machine language is weakly and dynamically typed. C++ is (mostly) strongly I have to disagree. A good machine language (one with no Catch Fire & Burn instructions) for a machine without programmer-visible caching is both strongly and statically typed, simply by virtue of the fact that all consequences of a given machine state are defined. You are making the mistake of imagining that addresses and ints and so forth exist in object code; but they don't. Those are abstractions in your mind. Ultimately they are NOT represented in the machine model. Bits go here, bits go there, the memory holds bits and nothing else. The (only) data type is the bit.... It's kind of trivial and uninteresting, but if Smalltalk is strongly typed then so is machine language (and by the same argument: all zero possible mis-assignments are successfully trapped); and if C is statically typed then so is machine language (because bits are stored in bits and that's the whole story). |[...] Isn't "segmentation violation" a "message not understood" message? Nope, it's a perfectly sensible part of instruction execution that is used heavily in the implementation of operating systems, memory managers and so forth. |It all depends on how you look at it. [...] Therefore the phenomenon's not really there in the langauage.... I'm really not trying to be silly here. The fact that machines are strongly typed underlyingly is the thing that makes secure implementations possible. If something could happen to be in memory that wasn't a bit, no language layered above could ever have guaranteed behaviour... (which is why it's bad when the hardware fails - untrapped type violations then CAN occur.... :-). It's sensible to ask, then, how we can implement UNTYPED langauges on top of this typed substrate. My guess is it's because memory is finite.... Which is to say, it's done with smoke & mirrors. ---------------------------------------------------------------------- stephen p spackman Center for Information and Language Studies systems analyst University of Chicago ----------------------------------------------------------------------