4 ms·

> The overhead (cognitive and in the implementation) of fexprs isn’t really worth the ability to do things like lazy evaluation and generators when there are al

by bsder 5y ago

> The overhead (cognitive and in the implementation) of fexprs isn’t really worth the ability to do things like lazy evaluation and generators when there are already perfectly adequate mechanisms available I would argue precisely the opposite. FEXPRs went away because they were too powerful. You don't need a macro system when you have FEXPRs as it doesn't buy you anything. Compiling FEXPRs can be difficult, however. Compiling MACROs is easy because they are, by definition, bounded--they just go from source-to-source (more on this later). And everybody in Lisp-land who weren't just computation theorists were obsessed with speed back then. So, FEXPRs had to go. Tcl is very close to FEXPRs; Shutt's thesis shows it just didn't quite go far enough. In addition, Steve Russell didn't add these to Lisp just because. Every piece of code was precious back in those days. If Steve Russell added it, he had a really good reason. I mean, he didn't even invent continuations until faced with mutual recursion. "quote" is actually the interloper--not FEXPRs. Even Alan Kay saw this way back. Quoting Alan Kay: > The biggest hit for me while at SAIL in late '69 was to really understand LISP. Of course, every student knew about car, cdr, and cons, but Utah was impoverished in that no one there used LISP and hence, no one had penetrated the mysteries of eval and apply. I could hardly believe how beautiful and wonderful the idea of LISP was [McCarthy 1960]. I say it this way because LISP had not only been around enough to get some honest barnacles, but worse, there were deep flaws in its logical foundations. By this, I mean that the pure language was supposed to be based on functions, but its most important components—such as lambda expressions, quotes, and conds—were not functions at all, and instead were called special forms. Landin and others had been able to get quotes and conds in terms of lambda by tricks that were variously clever and useful, but the flaw remained in the jewel. In the practical language things were better. There were not just EXPRs (which evaluated their arguments), but FEXPRs (which did not). My next question was, why on earth call it a functional language? Why not just base everything on FEXPRs and force evaluation on the receiving side when needed? I could never get a good answer ... So, even as far back as 1969, the fact that FEXPRs were "theoretically messy" was already causing them to be ignored. The "big thinkers" required source-to-source transformation or they couldn't publish papers--run-time interpretation need not apply. Look at how long "mutation" remained a "problem" in the theoretical computation community while FORTRAN just simply trundled along and solved people's problems. Now, think about what those same theoreticians would think about FEXPRs that takes "mutation" and turns it up to 11. The theoreticians simply banished FEXPRs rather than have to think about them.

matheusmoreira 5y ago
Thanks for explaining this. I've been wondering about why FEXPRs disappeared ever since the first time I read about them. Such a simple and elegant idea that for some reason was replaced by macros which are much harder to understand. Also explains why functions aren't lists of code fragments which you can manipulate.
DonHopkins 5y ago
>run-time interpretation need not apply ...because it can eval? ;) >Why not just base everything on FEXPRs and force evaluation on the receiving side when needed? PostScript is a lot like Lisp, where everything is an FEXPR. You pass around executable arrays to control flow functions like "if" and "for", and can write your own like "send". NeWS used an object oriented programming system that was a lot like Smalltalk with multiple inheritance, which leveraged the PostScript dictionary stack so it was quite efficient. PostScript object references (independent of the object it points to) can be executable or literal. Code in PostScript is represented by executable arrays, executable names are looked up on the dictionary stack, and their corresponding values are executed (literal arrays and other objects are pushed, executable arrays have their elements executed in order, etc.) As well as "send"ing an executable name to an object to execute a method by that name in its scope (by loading its instance/class/superclass/etc onto the dictionary stack), you could also "send" an executable array to an object to execute that code in the context of the object. (But that was not a common practice, just the way it happened to work because of how it was implemented.) James Gosling's Emacs Mocklisp was like FEXPRs on PCP, with support for prompting the user to supply omitted arguments. https://news.ycombinator.com/item?id=14312249 https://news.ycombinator.com/item?id=14312249 DonHopkins on May 10, 2017 | parent | context | favorite | on: Emacs is sexy Hey at least Elisp wasn't ever as bad as Mock Lisp, the extension language in Gosling (aka UniPress aka Evil Software Hoarder) Emacs. It had ultra-dynamic lazy scoping: It would defer evaluating the function parameters until they were actually needed by the callee (((or a function it called))), at which time it would evaluate the parameters in the CALLEE's scope. James Gosling honestly copped to how terrible a language MockLisp was in the 1981 Unix Emacs release notes: https://archive.org/stream/bitsavers_cmuGosling_4195808/Gosl https://archive.org/stream/bitsavers_cmuGosling_4195808/Gosl... 12.2. MLisp - Mock Lisp Unix Emacs contains an interpreter for a language that in many respects resembles Lisp. The primary (some would say only) resemblance between Mock Lisp and any real Lisp is the general syntax of a program, which many feel is Lisp's weakest point. The differences include such things as the lack of a cons function and a rather peculiar method of passing parameters. "Rather peculiar" is an understatement. More info, links and code examples: https://news.ycombinator.com/item?id=8727085 https://news.ycombinator.com/item?id=8727085 I was just recently writing about how PostScript is "homomorphicier" than Lisp, because it has a shorter more elegant Quine (but let's try not to think about BASIC): https://news.ycombinator.com/item?id=29929367 https://news.ycombinator.com/item?id=29929367 Speaking of writing PostScript with PostScript, Stan also wrote an elegant PostScript Quine, which is even shorter than the Lisp Quine (PostScript is like a cross between Lisp and Forth, but homomorphic and more like Lisp actually -- but PostScript is even homomorphicier than Lisp because it has an even shorter Quine!): https://www.donhopkins.com/home/archive/NeWS/news-tape/fun/q https://www.donhopkins.com/home/archive/NeWS/news-tape/fun/q... Date: Thu, 14 Sep 89 20:29:28 -0400 To: NeWS-makers@brillig.umd.edu Subject: A PostScript Quine From: spectral!sjs@bellcore.com (Stan Switzer) "'Yields falsehood when preceded by itself in quotes" yields falsehood when preceded by itself in quotes." -- W. V. O. Quine (paraphrase) A "quine" is a program which when evaluated yields its own representation. A quine can be formally described as a fixed point of a language's denotation function. Trivial evaluations (e.g.: literals) are excluded and the program cannot require any input data (e.g.: "cat cat.c"). In my experience, the merit of a language is inversely related to the length of its shortest quine. (Though I _am_ prejudiced toward reflective semantics.) For the heck of it, let's say a PostScript quine is a procedure "{...}" which when followed by "n { exec } repeat" yields the same (or equivalent) value for any non-negative integer value of "n" (including 0). The shortest I have found for PostScript is {{[ exch /dup load /exec load ] cvx} dup exec} Compare to Lisp: ((lambda(f)(list f (list 'quote f))) '(lambda(f)(list f (list 'quote f)))) or (ASCII) C: char*f="char*f=%c%s%c;main(){printf(f,042,f,042,012);}%c";main(){printf(f,042,f,042,012);} Not that it'll change your life or anything... Enjoy, Stan Switzer sjs@bellcore.com The only problem I have with Stan's theory about the merit of a language being inversely related to the length of its shortest Quine is the existence of "10 LIST" in BASIC, which is a decidedly un-meritorious language. But to its credit, DECSYSTEM 10 BASIC even has a "LISTREVERSE" command, which might be useful for implementing a Eniuq. For what it's worth, "10 LIST" and "10 LISTREVERSE" are also Line-by-Line Palendromic Quines, since single line programs are the same listed forwards and backwards. https://news.ycombinator.com/item?id=20007960 https://news.ycombinator.com/item?id=20007960 >LISTREVERSE and LISTNHREVERSE print the contents of the user's memory area in order of descending line numbers. LISTREVERSE precedes the output with a heading, LISTNHREVERSE eliminates the heading. Stan now works at Adobe (of course, how could they NOT hire him after he wrote that beautiful PostScript Quine! ;) ): https://www.linkedin.com/in/sjswitzer/ https://www.linkedin.com/in/sjswitzer/ Homomorphism: https://en.wikipedia.org/wiki/Homomorphism https://en.wikipedia.org/wiki/Homomorphism Quine: https://en.wikipedia.org/wiki/Quine_(computing) https://en.wikipedia.org/wiki/Quine_(computing) HyperLook SimCity Demo Transcript: This is a transcript of a video taped demonstration of SimCity on HyperLook in NeWS. https://donhopkins.medium.com/hyperlook-simcity-demo-transcript-17f627eab14a https://donhopkins.medium.com/hyperlook-simcity-demo-transcr... SimCity, Cellular Automata, and Happy Tool for HyperLook (nee HyperNeWS (nee GoodNeWS)): HyperLook was like HyperCard for NeWS, with PostScript graphics and scripting plus networking. Here are three unique and wacky examples that plug together to show what HyperNeWS was all about, and where we could go in the future! https://donhopkins.medium.com/hyperlook-nee-hypernews-nee-goodnews-99f411e58ce4 https://donhopkins.medium.com/hyperlook-nee-hypernews-nee-go...

by bsder 5y ago

matheusmoreira 5y ago

Thanks for explaining this. I've been wondering about why FEXPRs disappeared ever since the first time I read about them. Such a simple and elegant idea that for some reason was replaced by macros which are much harder to understand. Also explains why functions aren't lists of code fragments which you can manipulate.

DonHopkins 5y ago

>run-time interpretation need not apply ...because it can eval? ;) >Why not just base everything on FEXPRs and force evaluation on the receiving side when needed? PostScript is a lot like Lisp, where everything is an FEXPR. You pass around executable arrays to control flow functions like "if" and "for", and can write your own like "send". NeWS used an object oriented programming system that was a lot like Smalltalk with multiple inheritance, which leveraged the PostScript dictionary stack so it was quite efficient. PostScript object references (independent of the object it points to) can be executable or literal. Code in PostScript is represented by executable arrays, executable names are looked up on the dictionary stack, and their corresponding values are executed (literal arrays and other objects are pushed, executable arrays have their elements executed in order, etc.) As well as "send"ing an executable name to an object to execute a method by that name in its scope (by loading its instance/class/superclass/etc onto the dictionary stack), you could also "send" an executable array to an object to execute that code in the context of the object. (But that was not a common practice, just the way it happened to work because of how it was implemented.) James Gosling's Emacs Mocklisp was like FEXPRs on PCP, with support for prompting the user to supply omitted arguments. https://news.ycombinator.com/item?id=14312249 https://news.ycombinator.com/item?id=14312249 DonHopkins on May 10, 2017 | parent | context | favorite | on: Emacs is sexy Hey at least Elisp wasn't ever as bad as Mock Lisp, the extension language in Gosling (aka UniPress aka Evil Software Hoarder) Emacs. It had ultra-dynamic lazy scoping: It would defer evaluating the function parameters until they were actually needed by the callee (((or a function it called))), at which time it would evaluate the parameters in the CALLEE's scope. James Gosling honestly copped to how terrible a language MockLisp was in the 1981 Unix Emacs release notes: https://archive.org/stream/bitsavers_cmuGosling_4195808/Gosl https://archive.org/stream/bitsavers_cmuGosling_4195808/Gosl... 12.2. MLisp - Mock Lisp Unix Emacs contains an interpreter for a language that in many respects resembles Lisp. The primary (some would say only) resemblance between Mock Lisp and any real Lisp is the general syntax of a program, which many feel is Lisp's weakest point. The differences include such things as the lack of a cons function and a rather peculiar method of passing parameters. "Rather peculiar" is an understatement. More info, links and code examples: https://news.ycombinator.com/item?id=8727085 https://news.ycombinator.com/item?id=8727085 I was just recently writing about how PostScript is "homomorphicier" than Lisp, because it has a shorter more elegant Quine (but let's try not to think about BASIC): https://news.ycombinator.com/item?id=29929367 https://news.ycombinator.com/item?id=29929367 Speaking of writing PostScript with PostScript, Stan also wrote an elegant PostScript Quine, which is even shorter than the Lisp Quine (PostScript is like a cross between Lisp and Forth, but homomorphic and more like Lisp actually -- but PostScript is even homomorphicier than Lisp because it has an even shorter Quine!): https://www.donhopkins.com/home/archive/NeWS/news-tape/fun/q https://www.donhopkins.com/home/archive/NeWS/news-tape/fun/q... Date: Thu, 14 Sep 89 20:29:28 -0400 To: NeWS-makers@brillig.umd.edu Subject: A PostScript Quine From: spectral!sjs@bellcore.com (Stan Switzer) "'Yields falsehood when preceded by itself in quotes" yields falsehood when preceded by itself in quotes." -- W. V. O. Quine (paraphrase) A "quine" is a program which when evaluated yields its own representation. A quine can be formally described as a fixed point of a language's denotation function. Trivial evaluations (e.g.: literals) are excluded and the program cannot require any input data (e.g.: "cat cat.c"). In my experience, the merit of a language is inversely related to the length of its shortest quine. (Though I _am_ prejudiced toward reflective semantics.) For the heck of it, let's say a PostScript quine is a procedure "{...}" which when followed by "n { exec } repeat" yields the same (or equivalent) value for any non-negative integer value of "n" (including 0). The shortest I have found for PostScript is {{[ exch /dup load /exec load ] cvx} dup exec} Compare to Lisp: ((lambda(f)(list f (list 'quote f))) '(lambda(f)(list f (list 'quote f)))) or (ASCII) C: char*f="char*f=%c%s%c;main(){printf(f,042,f,042,012);}%c";main(){printf(f,042,f,042,012);} Not that it'll change your life or anything... Enjoy, Stan Switzer sjs@bellcore.com The only problem I have with Stan's theory about the merit of a language being inversely related to the length of its shortest Quine is the existence of "10 LIST" in BASIC, which is a decidedly un-meritorious language. But to its credit, DECSYSTEM 10 BASIC even has a "LISTREVERSE" command, which might be useful for implementing a Eniuq. For what it's worth, "10 LIST" and "10 LISTREVERSE" are also Line-by-Line Palendromic Quines, since single line programs are the same listed forwards and backwards. https://news.ycombinator.com/item?id=20007960 https://news.ycombinator.com/item?id=20007960 >LISTREVERSE and LISTNHREVERSE print the contents of the user's memory area in order of descending line numbers. LISTREVERSE precedes the output with a heading, LISTNHREVERSE eliminates the heading. Stan now works at Adobe (of course, how could they NOT hire him after he wrote that beautiful PostScript Quine! ;) ): https://www.linkedin.com/in/sjswitzer/ https://www.linkedin.com/in/sjswitzer/ Homomorphism: https://en.wikipedia.org/wiki/Homomorphism https://en.wikipedia.org/wiki/Homomorphism Quine: https://en.wikipedia.org/wiki/Quine_(computing) https://en.wikipedia.org/wiki/Quine_(computing) HyperLook SimCity Demo Transcript: This is a transcript of a video taped demonstration of SimCity on HyperLook in NeWS. https://donhopkins.medium.com/hyperlook-simcity-demo-transcript-17f627eab14a https://donhopkins.medium.com/hyperlook-simcity-demo-transcr... SimCity, Cellular Automata, and Happy Tool for HyperLook (nee HyperNeWS (nee GoodNeWS)): HyperLook was like HyperCard for NeWS, with PostScript graphics and scripting plus networking. Here are three unique and wacky examples that plug together to show what HyperNeWS was all about, and where we could go in the future! https://donhopkins.medium.com/hyperlook-nee-hypernews-nee-goodnews-99f411e58ce4 https://donhopkins.medium.com/hyperlook-nee-hypernews-nee-go...