Re: [TUHS] Mac OS X is Unix

Following on Doug's comment, when I wrote the portable C compiler my vision was to separate out the machine independent parts of the compiler (e.g, the lexer and parser) from the machine dependent parts (those parts involving stack frames, instructions, etc.).  Then to port the compiler, you could leave the machine independent code alone (much of which was rather hairy, involving symbol tables, optimizations, etc.) and simply describe the instructions and calling sequence in the machine dependent files.  The preprocessor was actually pretty important in carrying this out, because there were a fair number of machine characteristics ( such as byte order and word size) that were handled identically across different architectures but the actual values were different.  These were handled by defining some preprocessor macros. Several years later, I had moved to development and was responsible for shipping a variety of different compilers, most resting on the PCC base.  At one point, I was appalled to see that somebody had put some code into one of the machine-independent files that was bracketed with "# ifdef VAX".  There followed a most difficult conversation with the perpetrator who kept insisting that, after all, the code WAS the same on all machines... ----- Original Message ----- From: "Doug McIlroy" &lt;doug(a)cs.dartmouth.edu&gt; To:<tuhs@minnie.tuhs.org> Cc: Sent:Tue, 03 Jan 2017 15:19:08 -0500 Subject:Re: [TUHS] Mac OS X is Unix requires Curmudgeonly comment: I bristle at the coupling of "ifdef" and "portable". Ifdefs that adjust code for different systems are prima facie evidence of NON-portability. I'll buy "configurable" as a descriptor for such ifdef'ed code, but not "portable". And, while I am venting about ifdef: As a matter of sytle, ifdefs are global constructs. Yet they often have local effects like an if statement. Why do we almost always write #ifdef LINUX linux code #else default unix code #endif instead of the much cleaner if(LINUX) linux code else default unix code In early days the latter would have cluttered precious memory with unfreachable code, but now we have optimizing compilers that will excise the useless branch just as effectively as cpp. Much as the trait of overeating has been ascribed to our hunter ancestors' need to eat fully when nature provided, so overuse of ifdef echos coding practices tuned to the capabilities of bygone computing systems. "Ifdef hell" is a fitting image for what has to be one of Unix's least felicitous contributions to computing. Down with ifdef! Doug