Re: [Chicken-users] case vs. eq? - just curious ....
On Sat, Mar 3, 2012 at 3:31 PM, Peter Bex peter@xs4all.nl wrote: But the disadvantage is of course that it also means you can't use the power of these facilities when they are called for (see also the lack of general SLIME integration for Scheme). Precisely! Being able to introspect and patch code at runtime could lead to nifty development tools indeed, even if they were only available on 'csi'. -- Stephen *Kids these days.* *Whatever happened to hard work?* -- Joel Spolsky, The perils of javaschools ___ Chicken-users mailing list Chicken-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-users
Re: [Chicken-users] case vs. eq? - just curious ....
On Fri, Mar 02, 2012 at 06:57:56PM -0700, Matt Welland wrote: I'm trying to convert a comparison operator to the equivalent text. These are not symbols. I think case treats the target list as if it was created with a quote: '(). Thus things are all symbols in the list and the eqv? returns false. (case (() yup)(else nope)) nope (cond ((eqv? ) yup)(else nope)) yup The cond does what I need just fine, I just didn't understand why case didn't also work. Like others have said before, case implicitly quotes its arguments, comparing the input to symbols. Your cond is doing something entirely different; taking the value of the identifiers and comparing the input to those. Is there a more schemeish way to convert any of the operators to the text representation? (define gt ) (op-string gt) = I think you're perhaps confused about the difference between one of many possible textual representations of a program and its semantical meaning. How is Scheme supposed to know the canonical name of a random lambda? The only way is whatever arbitrarily chosen assignment you've decided on in your program. Having said that, you can extract the initial name of a procedure, which is the name of the surrounding define when the lambda was first introduced (or its C name in some cases): #;1 (define (bar x) 1) #;2 (define foo (lambda (y) y)) #;3 (let ((whatever (lambda (z) z))) ;; set! global value (set! qux whatever)) #;4 (##sys#lambda-info-string (##sys#lambda-info bar)) (bar x) #;5 (##sys#lambda-info-string (##sys#lambda-info foo)) (foo y) #;6 (##sys#lambda-info-string (##sys#lambda-info qux)) (whatever z) #;7 (##sys#lambda-info-string (##sys#lambda-info +)) C_plus #;8 ;; But look at this: (use numbers) #;9 (##sys#lambda-info-string (##sys#lambda-info +)) (numbers#+ . args176) As you can see, this canonical name isn't something you can easily influence. Another way to solve this particilar issue is to make an alist or hash table mapping your desired canonical names to procedures, and op-string look up names in this table. A macro might also help in reducing work, as it allows you to list just the canonical names of procedures once and have it generate a case statement: #;1 (define-syntax define-op-converter (syntax-rules () ((_ name op0 ...) (define (name op) (select op ((op0) (symbol-string 'op0)) ... (else (error unknown operator op))) #;2 (define-op-converter op-string + -) #;3 (op-string ) #;4 ;; But there are many limitations: (use numbers) #;5 (op-string ) Error: unknown operator: #procedure (numbers# x11875 x21876 . xs1877) Depending on what exactly you're trying to do in the bigger picture, perhaps rethinking your approach is a better solution than trying to work around this. Cheers, Peter -- http://sjamaan.ath.cx -- The process of preparing programs for a digital computer is especially attractive, not only because it can be economically and scientifically rewarding, but also because it can be an aesthetic experience much like composing poetry or music. -- Donald Knuth ___ Chicken-users mailing list Chicken-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-users
Re: [Chicken-users] case vs. eq? - just curious ....
On Sat, Mar 3, 2012 at 6:53 AM, Peter Bex peter@xs4all.nl wrote: On Fri, Mar 02, 2012 at 06:57:56PM -0700, Matt Welland wrote: I'm trying to convert a comparison operator to the equivalent text. These are not symbols. I think case treats the target list as if it was created with a quote: '(). Thus things are all symbols in the list and the eqv? returns false. (case (() yup)(else nope)) nope (cond ((eqv? ) yup)(else nope)) yup The cond does what I need just fine, I just didn't understand why case didn't also work. Like others have said before, case implicitly quotes its arguments, comparing the input to symbols. Your cond is doing something entirely different; taking the value of the identifiers and comparing the input to those. Is there a more schemeish way to convert any of the operators to the text representation? (define gt ) (op-string gt) = I think you're perhaps confused about the difference between one of many possible textual representations of a program and its semantical meaning. How is Scheme supposed to know the canonical name of a random lambda? The only way is whatever arbitrarily chosen assignment you've decided on in your program. Having said that, you can extract the initial name of a procedure, which is the name of the surrounding define when the lambda was first introduced (or its C name in some cases): It sounds like the answer I was looking for is that there is no scheme introspection that maps a procedure to the bound name. The question was merely academic, the cond is fine. I like the select but prefer not to use it as it may not be available out of the box should I ever need to migrate to another scheme. #;1 (define (bar x) 1) #;2 (define foo (lambda (y) y)) #;3 (let ((whatever (lambda (z) z))) ;; set! global value (set! qux whatever)) #;4 (##sys#lambda-info-string (##sys#lambda-info bar)) (bar x) #;5 (##sys#lambda-info-string (##sys#lambda-info foo)) (foo y) #;6 (##sys#lambda-info-string (##sys#lambda-info qux)) (whatever z) #;7 (##sys#lambda-info-string (##sys#lambda-info +)) C_plus #;8 ;; But look at this: (use numbers) #;9 (##sys#lambda-info-string (##sys#lambda-info +)) (numbers#+ . args176) As you can see, this canonical name isn't something you can easily influence. Another way to solve this particilar issue is to make an alist or hash table mapping your desired canonical names to procedures, and op-string look up names in this table. A macro might also help in reducing work, as it allows you to list just the canonical names of procedures once and have it generate a case statement: #;1 (define-syntax define-op-converter (syntax-rules () ((_ name op0 ...) (define (name op) (select op ((op0) (symbol-string 'op0)) ... (else (error unknown operator op))) #;2 (define-op-converter op-string + -) #;3 (op-string ) #;4 ;; But there are many limitations: (use numbers) #;5 (op-string ) Error: unknown operator: #procedure (numbers# x11875 x21876 . xs1877) Depending on what exactly you're trying to do in the bigger picture, perhaps rethinking your approach is a better solution than trying to work around this. Thanks for the detailed analysis. I probably should have been clearer, I was merely wondering if there was some slick introspection available in scheme that would make this general and easy. My problem is trivial and the cond solves it just fine. The macro you wrote above is very interesting. Although for the reasons you pointed out I won't be using it I did get to learn something. Thanks to all who replied. Cheers, Peter -- http://sjamaan.ath.cx -- The process of preparing programs for a digital computer is especially attractive, not only because it can be economically and scientifically rewarding, but also because it can be an aesthetic experience much like composing poetry or music. -- Donald Knuth ___ Chicken-users mailing list Chicken-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-users ___ Chicken-users mailing list Chicken-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-users
Re: [Chicken-users] case vs. eq? - just curious ....
On Sat, Mar 03, 2012 at 11:14:34AM -0700, Matt Welland wrote: It sounds like the answer I was looking for is that there is no scheme introspection that maps a procedure to the bound name. It was part of my point that there is no the bound name, there can be several. What would this return? (define x (lambda (y) (lambda () y))) (name-of (x)) Or this: (define (a b c) (apply b c)) (define gt ) (a (list gt)) There can be many things that are aliases for the same procedure. Thanks for the detailed analysis. I probably should have been clearer, I was merely wondering if there was some slick introspection available in scheme that would make this general and easy. Contrary to popular belief and other Lisps, Scheme is really quite a static language and lacks many of the more dynamic introspection facilities of languages and systems like CLOS, Ruby or (shudder!) PHP. This is generally a good thing, as it allows for pretty efficient compilation and these introspection things only allow people to paint themselves into a corner. Introspection allows cutting through the language's abstraction barriers (which are there for a reason!) which makes it too easy to write code riddled with assumptions about how the other person's code is supposed to work. Of course this kind of code breaks the minute the other code makes internal changes (think monkey-patching). But the disadvantage is of course that it also means you can't use the power of these facilities when they are called for (see also the lack of general SLIME integration for Scheme). Although for the reasons you pointed out I won't be using it I did get to learn something. I'm glad to hear that I've provided some useful insights! Cheers, Peter -- http://sjamaan.ath.cx -- The process of preparing programs for a digital computer is especially attractive, not only because it can be economically and scientifically rewarding, but also because it can be an aesthetic experience much like composing poetry or music. -- Donald Knuth ___ Chicken-users mailing list Chicken-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-users
Re: [Chicken-users] case vs. eq? - just curious ....
Peter Bex scripsit: Contrary to popular belief and other Lisps, Scheme is really quite a static language and lacks many of the more dynamic introspection facilities of languages and systems like CLOS, Ruby or (shudder!) PHP. Don't forget Python, where even definitions are executable. Though modern Scheme is not as static as R4RS or ISLisp, where there is not even `eval`. (Of course these languages are not static in the sense of static typing.) -- John Cowanco...@ccil.orghttp://ccil.org/~cowan The present impossibility of giving a scientific explanation is no proof that there is no scientific explanation. The unexplained is not to be identified with the unexplainable, and the strange and extraordinary nature of a fact is not a justification for attributing it to powers above nature. --The Catholic Encyclopedia, s.v. telepathy (1913) ___ Chicken-users mailing list Chicken-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-users
Re: [Chicken-users] case vs. eq? - just curious ....
On Sat, Mar 03, 2012 at 02:06:56PM -0500, John Cowan wrote: Don't forget Python, where even definitions are executable. Though modern Scheme is not as static as R4RS or ISLisp, where there is not even `eval`. (Of course these languages are not static in the sense of static typing.) I don't have more than a passing familiarity with Python, so I had to look up what you meant by definitions are executable, and I didn't like what I found :) Guide himself talks about this here: http://python-history.blogspot.com/2009/03/how-everything-became-executable.html PHP has this problem as well. PHP even allows included files and EVALed code to access local lexical variables in the calling function. I've often seen newbies in #scheme or #chicken who were confused by this, and tried to graft similar functionality on top of Scheme (which is utterly doomed to fail, of course) And don't get me started on Javascript with its idiotic hoisting concept... Cheers, Peter -- http://sjamaan.ath.cx -- The process of preparing programs for a digital computer is especially attractive, not only because it can be economically and scientifically rewarding, but also because it can be an aesthetic experience much like composing poetry or music. -- Donald Knuth ___ Chicken-users mailing list Chicken-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-users
Re: [Chicken-users] case vs. eq? - just curious ....
Peter Bex scripsit: Guide himself talks about this here: http://python-history.blogspot.com/2009/03/how-everything-became-executable.html Fascinating. I'm working my way through the entire blog (fortunately only 26 posts) even as we speak. PHP has this problem as well. PHP even allows included files and EVALed code to access local lexical variables in the calling function. I've often seen newbies in #scheme or #chicken who were confused by this, and tried to graft similar functionality on top of Scheme (which is utterly doomed to fail, of course) Whew. I'm certainly glad I always stayed ten miles away from any PHP code. And don't get me started on Javascript with its idiotic hoisting concept... There are advantages to the scope of a declaration extending before the declaration; it means you don't have to have special syntax to forward-declare a name before you can use it in mutual recursion. But basically I agree, especially for Scheme syntax declarations. See The Tale of Professor Simpleton and Dr. Hardcase at http://lists.r6rs.org/pipermail/r6rs-discuss/2009-September/005487.html . -- John Cowanco...@ccil.org Yakka foob mog. Grug pubbawup zink wattoom gazork. Chumble spuzz. --Calvin, giving Newton's First Law in his own words ___ Chicken-users mailing list Chicken-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-users
[Chicken-users] case vs. eq? - just curious ....
I expected this to work: (define (comp-text comp) (case comp ((=)=) (()) (()) ((=) =) ((=) =) (else unk))) But had to convert to a cond with (eq? comp =) etc... I thought case was supposed to use eq? to do the compare? Thanks, M a t t -=- ___ Chicken-users mailing list Chicken-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-users
Re: [Chicken-users] case vs. eq? - just curious ....
On Mar 2, 2012, at 3:52 PM, Matt Welland wrote: I expected this to work: (define (comp-text comp) (case comp ((=)=) (()) (()) ((=) =) ((=) =) (else unk))) But had to convert to a cond with (eq? comp =) etc... Are =, , etc variables? 'case' quotes the objects in each case. So comparing against symbols. (##core#let ((tmp '=)) (##core#if (or (eqv? tmp '=)) (##core#begin =) (##core#if ... I thought case was supposed to use eq? to do the compare? eqv? Thanks, M a t t -=- ___ Chicken-users mailing list Chicken-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-users ___ Chicken-users mailing list Chicken-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-users
Re: [Chicken-users] case vs. eq? - just curious ....
eqv?, to be exact. Your case statement works fine for me, with for example (comp-text '=). (eq? comp =) compares against the value of the procedure =, whereas the case compares against the symbol =. So you are doing two different comparisons. You can use ,x (case ...) at the REPL to see what the case expands to. Fake edit: Kon said this more succinctly than I did. Jim On Mar 2, 2012, at 5:52 PM, Matt Welland wrote: I expected this to work: (define (comp-text comp) (case comp ((=)=) (()) (()) ((=) =) ((=) =) (else unk))) But had to convert to a cond with (eq? comp =) etc... I thought case was supposed to use eq? to do the compare? ___ Chicken-users mailing list Chicken-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-users
Re: [Chicken-users] case vs. eq? - just curious ....
On Fri, Mar 2, 2012 at 5:04 PM, Jim Ursetto zbignie...@gmail.com wrote: eqv?, to be exact. Your case statement works fine for me, with for example (comp-text '=). (eq? comp =) compares against the value of the * procedure* =, whereas the case compares against the symbol =. So you are doing two different comparisons. I'm trying to convert a comparison operator to the equivalent text. These are not symbols. I think case treats the target list as if it was created with a quote: '(). Thus things are all symbols in the list and the eqv? returns false. (case (() yup)(else nope)) nope (cond ((eqv? ) yup)(else nope)) yup The cond does what I need just fine, I just didn't understand why case didn't also work. Is there a more schemeish way to convert any of the operators to the text representation? (define gt ) (op-string gt) = You can use *,x (case ...)* at the REPL to see what the case expands to. Fake edit: Kon said this more succinctly than I did. Jim On Mar 2, 2012, at 5:52 PM, Matt Welland wrote: I expected this to work: (define (comp-text comp) (case comp ((=)=) (()) (()) ((=) =) ((=) =) (else unk))) But had to convert to a cond with (eq? comp =) etc... I thought case was supposed to use eq? to do the compare? ___ Chicken-users mailing list Chicken-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-users
Re: [Chicken-users] case vs. eq? - just curious ....
On Mar 2, 2012, at 7:57 PM, Matt Welland wrote: I'm trying to convert a comparison operator to the equivalent text. These are not symbols. I think case treats the target list as if it was created with a quote: '(). That's what case does. You want `select`: http://api.call-cc.org/doc/chicken/special-forms/select . The cond does what I need just fine, I just didn't understand why case didn't also work. Expand it with ,x and you'll see. Jim ___ Chicken-users mailing list Chicken-users@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-users
