Re: [Chicken-hackers] substring function and bounds checks
On Fri, Feb 8, 2013 at 8:41 AM, Alex Shinn alexsh...@gmail.com wrote: On Fri, Feb 8, 2013 at 4:21 PM, Michele La Monaca mikele.chic...@lamonaca.net wrote: On Fri, Feb 8, 2013 at 5:43 AM, Alex Shinn alexsh...@gmail.com wrote: operations. The only example provided was fairly obscure and it was indeed a composition, even if you don't think it's worth separating them for logging or other handling. At the prompt of your shell type: # ls ?a_well_thought_out_substring_function_would_do_this_job* I'm not sure I understand, but it sounds like you're just mocking me? Not at all! Sorry if I gave you that impression. Ok, there was a bit of humor, but, well, take it easy. Rember Jim calling Sussman on the phone only to be redirected to voicemail? I think this kind of jokes are accettable in a heated technical discussion and no one should get offended for those. Anyway, mine wasn't only a joke. I used to be a C programmer so I have the bad habit to condense too much information in one line. Sorry for that. If you want I can expand on it and explain my case. Unfortunately I think I've already abused enough this list, so feel free to contact me privately if you want to continue this discussion with me. Regards, Michele ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
From: Alex Shinn alexsh...@gmail.com Subject: Re: [Chicken-hackers] substring function and bounds checks Date: Fri, 8 Feb 2013 10:33:33 +0900 On Fri, Feb 8, 2013 at 10:14 AM, Michele La Monaca mikele.chic...@lamonaca.net wrote: starting from a certain position give me chars up to the Nth position or up to the end of the string whatever the first Can you provide a real-world example where you'd want to use this function? Ugh. Whenever a language/API/system design discussion goes into this stage, it's best to stop. Can't we just allow Michele to have his own opinion? Let's leave him alone now, and let's start getting productive. cheers, felix ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
On Thu, Feb 7, 2013 at 12:20 AM, Alex Shinn alexsh...@gmail.com wrote: Hi, On Thu, Feb 7, 2013 at 3:20 AM, Michele La Monaca mikele.chic...@lamonaca.net wrote: [..] I don't think (substring2 foo 0 10) - foo is conceptually wrong or sloppy as long as you know exactly what the semantic of the function is (give me at most N chars - perl or give me chars up to the Nth position or up to the end of the string whatever the first - python, ruby). Truncating a string to a maximum length is a common operation for formatting - I was surprised there was no easy way to do this with SRFI-13. But in this case the start argument isn't needed and distracting. You probably want something like: Well, no. If I wanted a truncate function I would have asked for it. I used 0 as START to simplify the exposition (in that case the END parameter can be interpreted as length or position indifferently). Anyway, thanks for raising the point. Maybe the reason there is no string-truncate around is that a sane substring function would just do the job? Regards, Michele (string-truncate foo 10) = foo (string-truncate foofoofoofoo 10) = foofoofoof In the fmt egg: (fmt #f (trim 10 foo)) = foo Conflating this with substring is confusing and hides potential errors, as others have pointed out. -- Alex ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
On Wed, Feb 6, 2013 at 12:47 AM, Felix fe...@call-with-current-continuation.org wrote: # perl -e 'print substr(ciao,0,10);' ciao # ruby -e 'puts ciao[0..10]' ciao # python -c 'print ciao[0:10];' ciao # csi -e '(print (substring ciao 0 10))' Error: (substring) out of range 0 10 Call history: syntax (print (substring ciao 0 10)) syntax (substring ciao 0 10) eval(print (substring ciao 0 10)) eval(substring ciao 0 10) -- The string is shorter than the limit you gave to substring in the third argument. Of course you know that, but why did you pass an incorrect length in the first place? This looks like it does what you want: csi -e '(print (substring ciao 0))' Well, no. I was looking for a python-like substring function. Anyway, thanks for the (substring ciao 0) trick, it is a very handy method to trim strings on the left (not documented in the wiki, btw): (substring ciao 1) = iao In my ideal world, there would room also for that: (substring ciao 0 -1) = cia but I know, I know... it will never happen :-( Regards, Michele ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
Michele La Monaca scripsit: Well, no. I was looking for a python-like substring function. If that's all you really wanted, the slice egg (to which you have already been referred; docs at http://wiki.call-cc.org/eggref/4/slice) does everything you are asking for, negative and past-the-end indices and all. It even slices lists and vectors as a bonus. But no, what you are showing you actually want is to complain about the meaning of the name substring. That's not a discussion anyone else thinks is worth having. -- You are a child of the universe no less John Cowan than the trees and all other acyclichttp://www.ccil.org/~cowan graphs; you have a right to be here.co...@ccil.org --DeXiderata by Sean McGrath ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
On Fri, Feb 8, 2013 at 2:23 AM, Michele La Monaca mikele.chic...@lamonaca.net wrote: On Thu, Feb 7, 2013 at 12:20 AM, Alex Shinn alexsh...@gmail.com wrote: Hi, On Thu, Feb 7, 2013 at 3:20 AM, Michele La Monaca mikele.chic...@lamonaca.net wrote: [..] I don't think (substring2 foo 0 10) - foo is conceptually wrong or sloppy as long as you know exactly what the semantic of the function is (give me at most N chars - perl or give me chars up to the Nth position or up to the end of the string whatever the first - python, ruby). Truncating a string to a maximum length is a common operation for formatting - I was surprised there was no easy way to do this with SRFI-13. But in this case the start argument isn't needed and distracting. You probably want something like: Well, no. If I wanted a truncate function I would have asked for it. I used 0 as START to simplify the exposition (in that case the END parameter can be interpreted as length or position indifferently). You didn't use it just to simplify, because the task you described in English was give me at most N chars. This is a common task, and always has a START of 0. There may be cases in Python where you first want to take the substring from START to the end of the string, and then want to truncate the result to END-START chars. This becomes an idiom in Python, so it seems natural to you, but there is always a specific reason you want to truncate separate from the substring you are taking. In Scheme this becomes (string-truncate (string-copy str start) max-len) You could combine these two functions (slice str start (- max-len start)) but this hides what you're actually doing and likely not as common, so is probably a bad idiom in Scheme. It doesn't make sense to provide such artificially combined functions. For example, you may notice sometimes you want to take a substring and then lowercase the result, but that doesn't mean it's worth defining a substring-downcase function. To add to the earlier rants abouts the dangers of DWIM behavior, I had a nasty bug in one of my Python programs the other day. We have an API for tasks which produce file outputs, and for convenience if there's only a single output we just return that, otherwise we return a tuple of strings. I had a task where I wanted to copy the first result to a separate directory, and this was a task that returned a tuple, so I used outputs[0]. Unfortunately, after some refactoring this became a task which only returned one output, so outputs became a string and outputs[0] was /! The program was still perfectly valid, and gave me the command-line: cp -R / /path/to/destination Fortunately we have lots of extra checks and I caught this before ever executing it, but it was scary to even just see that. -- Alex ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
How strange, I thought no one was interested in the discussion. Anyway, with John's permission just a few inline clarifications. On Thu, Feb 7, 2013 at 11:59 PM, Alex Shinn alexsh...@gmail.com wrote: [...] You didn't use it just to simplify, because the task you described in English was give me at most N chars. http://lists.nongnu.org/archive/html/chicken-hackers/2013-02/msg00058.html give me at most N chars starting from a certain position in the string Ok, in another mail I gave a shortened version but, well, I think the context was clear. This is a common task, and always has a START of 0. What? what? what? There may be cases in Python where you first want to take the substring from START to the end of the string, and then want to truncate the result to END-START chars. This becomes an idiom in Python, so it seems natural to Sorry, never used Python in my life. I used it as an example because I think it's a commonly known language. Not by me, unfortunately, so I don't believe I completely understand what you are trying to say. you, but there is always a specific reason you want to truncate separate from the substring you are taking. In Scheme this becomes (string-truncate (string-copy str start) max-len) You could combine these two functions (slice str start (- max-len start)) but this hides what you're actually doing Don't think so. Really don't think so. and likely not as common, so is probably a bad idiom in Scheme. It doesn't make sense to provide such artificially combined functions. Again (last time I promise), I don't think that: starting from a certain position give me at most N chars or starting from a certain position give me chars up to the Nth position or up to the end of the string whatever the first are artificially combined functions. They are exactly what they mean. Anyway, I think I had enough of that. I respect your opinions, please try to respect mine and let's stop this discussion. Regards, Michele ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
On Fri, Feb 8, 2013 at 10:14 AM, Michele La Monaca mikele.chic...@lamonaca.net wrote: starting from a certain position give me chars up to the Nth position or up to the end of the string whatever the first Can you provide a real-world example where you'd want to use this function? -- Alex ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
Alex Shinn scripsit: Can you provide a real-world example where you'd want to use this function? I used to use it all the time in Perl, where it is the normal behavior of the substr() function, to pull a fixed-width field out of a line of text without having to worry about short lines. If the field was at the end of the line, the result was short; if the field was not present, the result was the empty string. In some contexts, I would then concatenate spaces to it and truncate the result to the desired width. -- Barry thirteen gules and argent on a canton azure John Cowan fifty mullets of five points of the second, co...@ccil.org six, five, six, five, six, five, six, five, and six. --blazoning the U.S. flag http://www.ccil.org/~cowan ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
On Fri, Feb 8, 2013 at 10:45 AM, John Cowan co...@mercury.ccil.org wrote: Alex Shinn scripsit: Can you provide a real-world example where you'd want to use this function? I used to use it all the time in Perl, where it is the normal behavior of the substr() function, to pull a fixed-width field out of a line of text without having to worry about short lines. If the field was at the end of the line, the result was short; This is where you have a contradiction - the field is fixed width but the full width is not available, which means you have an invalid format. Could you be more specific in your example? If the goal is to extract the last field, then you use substr with no end param. If the goal is to take a fixed field you should be taking that. If the format allows either then the format itself is ambiguous, which means you have a _much_ bigger problem than whatever language idioms you use. -- Alex ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
Alex Shinn scripsit: This is where you have a contradiction - the field is fixed width but the full width is not available, which means you have an invalid format. Yes, in one sense. However, when transferring textual data between heterogeneous systems it is very common for trailing spaces to be discarded willy-nilly, and the approach described recovers from that nicely. Be liberal in what you accept. If the goal is to take a fixed field you should be taking that. If the format allows either then the format itself is ambiguous, which means you have a _much_ bigger problem than whatever language idioms you use. Purism has its place, but is not always the appropriate response to Real World issues. In this case, kicking back such records as invalid/ambiguous format simply would not have served the organization's goals. -- In my last lifetime,John Cowan I believed in reincarnation;http://www.ccil.org/~cowan in this lifetime, co...@ccil.org I don't. --Thiagi ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
On Fri, Feb 8, 2013 at 11:50 AM, John Cowan co...@mercury.ccil.org wrote:
Alex Shinn scripsit:
If the goal is to take a fixed field you should be taking that. If
the format allows either then the format itself is ambiguous, which
means you have a _much_ bigger problem than whatever language
idioms you use.
Purism has its place, but is not always the appropriate response
to Real World issues. In this case, kicking back such records
as invalid/ambiguous format simply would not have served the
organization's goals.
I was not suggesting kicking it back. I was suggesting if it
was the last field then just use substr($line, $n). That sounds
like the definition of the format you're describing, though you're
not giving a concrete example so I can't be sure.
If there are additional restraints on this field then you should
handle them as well, and if you want to handle those restraints
liberally you can do so. For example, if the length of the last
field should be no longer than $limit, you can check this:
if (len($field) $limit) {
print STDERR found trailing junk at end of line: $field;
$field = substr($field, 0, $limit);
}
The warning is important, and this again emphasizes that there
are two _unrelated_ functions - extraction and truncation - and
that combining them is a bad idea.
--
Alex
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Re: [Chicken-hackers] substring function and bounds checks
Alex Shinn scripsit: The warning is important, and this again emphasizes that there are two _unrelated_ functions - extraction and truncation - and that combining them is a bad idea. The warning is important -- when it's important. In my case, it was important to avoid cluttering the exception log with spurious complaints about the results of a process outside anyone's control. In any case, that has zero to do with whether it makes sense to package this behavior as a procedural abstraction. Please note that I am *not* arguing that Chicken's substring should behave this way, just that a convenient implementation of the loose behavior does have use cases. -- The Imperials are decadent, 300 pound John Cowan co...@ccil.org free-range chickens (except they have http://www.ccil.org/~cowan teeth, arms instead of wings, and dinosaurlike tails).--Elyse Grasso ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
On Fri, Feb 8, 2013 at 12:26 PM, John Cowan co...@mercury.ccil.org wrote: Alex Shinn scripsit: The warning is important, and this again emphasizes that there are two _unrelated_ functions - extraction and truncation - and that combining them is a bad idea. The warning is important -- when it's important. In my case, it was important to avoid cluttering the exception log with spurious complaints about the results of a process outside anyone's control. Then comment out the logging, or use a verbosity level. The most important thing with a hacky language and hacky formats is to be precise about your parsing. In any case, that has zero to do with whether it makes sense to package this behavior as a procedural abstraction. Please note that I am *not* arguing that Chicken's substring should behave this way, just that a convenient implementation of the loose behavior does have use cases. I think none of the Schemers are arguing that substring should be changed. I'm arguing further that the slice function is an artifact of languages that have slicing as syntax, but here is actually a confused composition of two operations. The only example provided was fairly obscure and it was indeed a composition, even if you don't think it's worth separating them for logging or other handling. -- Alex ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
On Fri, Feb 8, 2013 at 5:43 AM, Alex Shinn alexsh...@gmail.com wrote: operations. The only example provided was fairly obscure and it was indeed a composition, even if you don't think it's worth separating them for logging or other handling. At the prompt of your shell type: # ls ?a_well_thought_out_substring_function_would_do_this_job* Regards, Michele ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
Hi Peter, wow! What a long and articulate response! Thanks for that, I really appreciate the time and effort you put in it. I also understand (and appreciate again) your attempt to inculcate in me a different way of thinking, but unfortunately, at least for now, my antibodies are at work. Maybe one day... for now I am just comfortable with my few little beliefs. Excuse me if I have been somehow rude but, you know, we both have strong ideas. Today is my boring gym day, so I have to condense my reply somehow and, anyway, I don't want to repeat myself over and over. As I said: (substring1 foo 0 10) - bump (substring2 foo 0 10) - foo are both legitimate scheme substring functions from what I can tell. You say the first is the non-sloppy, safer one, I just say they have a different semantic and I do notice that we have a rather different concept of safety. Indeed, I don't think (substring2 foo 0 10) - foo is conceptually wrong or sloppy as long as you know exactly what the semantic of the function is (give me at most N chars - perl or give me chars up to the Nth position or up to the end of the string whatever the first - python, ruby). Regarding the practical aspects of the issue, I hope you might agree with me that substring2 if far superior to substring1. Having to catch exceptions, or having to write a wrapper function, as Jim suggested, to achieve a minimal sane usage of substring1 (and hey we are not talking about the apollo11-land-on-the-moon-button function), should give you a sense of the inadequacy of the substring function currently shipped with chicken. Anyway, as you suggested, maybe it is just too early for me... let's see. (I hope) I am the kind of person which periodically reconsider without preconceptions his beliefs and principles, though, admittedly, I am rather defensive at the beginning. Thanks to the community for all the kind responses. Regards, Michele On Wed, Feb 6, 2013 at 10:21 AM, Peter Bex peter@xs4all.nl wrote: On Wed, Feb 06, 2013 at 12:55:16AM +0100, Michele La Monaca wrote: What I can say... Well, maybe one day I will see the light, in the meanwhile I would just have preferred a more useful substring function. I really think that the one provided by chicken is simply not on par with other languages, sorry. This is not a question of being on par or not. Some other languages choose to have nonsensical requests like give me characters 0 through 10 from this 3-character string to return the original string. Substring is a silly and trivial example but it clearly illustrates the deep fundamental differences in philosophy between the different cultures of these languages. The most valuable gift a computer programming language can give you is the ability to reason about a piece of code without extra information. For example, if you see (substring s 0 10) you immediately *know* in any code that follows: - The variable s is a string - The string s is at least 10 characters long - The returned value is a string - The returned string is exactly 10 characters long If none of the above are true, you'll have an error situation and the code following the substring call will not be executed. In sloppy languages, you lose several of these important footholds, which means you can't reason so well about your code's correctness anymore, except by reading back and dragging in more context. The above guarantees mean, for example, that if later you see (string-ref s 8) this will *always* return a character. In your other languages, you won't know what exactly it'll do. You'll have two lines of possible future traces through your program: one where there was a character and one where there wasn't. Multiply this by every sloppy operator you use and you end up with a tangled web of possible futures. Often, only one of those futures is what you had in mind when writing code. The other possibilities produce wrong computations, which may result in data corruption or security problems. Sloppiness promotes muddled thinking and imprecise code. Imprecise code is prone to bugs, which may lead to security problems. This may not be fair, but I think a particularly good example is the 2 recent extremely dangerous vulnerabilities in Ruby on Rails which allowed for remote code execution. What caused these problems to happen? Misplaced convenience and sloppiness: Rails allowed Yaml data to be embedded in XML and JSON, which automatically got parsed. Of course, XML and JSON are their own formats and their specifications don't mention anything about Yaml. This means a Yaml parser has nothing, and I mean *nothing* to do in an XML parser. It may be convenient in a small set of cases, but it's just another case of adding more magic: it's not something you asked for, so it shouldn't happen. For another good example of the deep confusion caused by code that is sloppy by design, read https://bugs.php.net/bug.php?id=54547 Read it, and also
Re: [Chicken-hackers] substring function and bounds checks
Michele La Monaca scripsit: Regarding the practical aspects of the issue, I hope you might agree with me that substring2 if far superior to substring1. All you're arguing now is that it's substring2 that deserves the name substring, since the slice function already does what you want. That's plain silly. Go ahead and use slice if you think it's more practical. give you a sense of the inadequacy of the substring function currently shipped with chicken. It's inadequate to your purposes, but it's adequate to other people's purposes, and vice versa for the function you want. -- Take two turkeys, one goose, four John Cowan cabbages, but no duck, and mix them http://www.ccil.org/~cowan together. After one taste, you'll duck co...@ccil.org soup the rest of your life. --Groucho ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
Hi, On Thu, Feb 7, 2013 at 3:20 AM, Michele La Monaca mikele.chic...@lamonaca.net wrote: [..] I don't think (substring2 foo 0 10) - foo is conceptually wrong or sloppy as long as you know exactly what the semantic of the function is (give me at most N chars - perl or give me chars up to the Nth position or up to the end of the string whatever the first - python, ruby). Truncating a string to a maximum length is a common operation for formatting - I was surprised there was no easy way to do this with SRFI-13. But in this case the start argument isn't needed and distracting. You probably want something like: (string-truncate foo 10) = foo (string-truncate foofoofoofoo 10) = foofoofoof In the fmt egg: (fmt #f (trim 10 foo)) = foo Conflating this with substring is confusing and hides potential errors, as others have pointed out. -- Alex ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
[Chicken-hackers] substring function and bounds checks
Maybe this is not the right list for that, sorry. But is there a good reason for this behavior? # perl -e 'print substr(ciao,0,10);' ciao # ruby -e 'puts ciao[0..10]' ciao # python -c 'print ciao[0:10];' ciao # csi -e '(print (substring ciao 0 10))' Error: (substring) out of range 0 10 Call history: syntax (print (substring ciao 0 10)) syntax (substring ciao 0 10) eval(print (substring ciao 0 10)) eval(substring ciao 0 10) -- I find it rather inconvenient and I can't really see any good reason to do that. In fact, it makes the usage of substring unsafe and the countermeasures I can imagine (manual bounds checks, padding, writing my-own-substring-function, whatever) are quite unsatisfactory... to me at least. Regards, Michele ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
On Tue, Feb 05, 2013 at 11:11:51PM +0100, Michele La Monaca wrote: Maybe this is not the right list for that, sorry. But is there a good reason for this behavior? Yes, sanity. # perl -e 'print substr(ciao,0,10);' ciao Perl is extremely sloppy. # ruby -e 'puts ciao[0..10]' ciao Ruby is just Perl in OOP clothing. # python -c 'print ciao[0:10];' ciao Python should know better. # csi -e '(print (substring ciao 0 10))' Error: (substring) out of range 0 10 Call history: syntax (print (substring ciao 0 10)) syntax (substring ciao 0 10) eval(print (substring ciao 0 10)) eval(substring ciao 0 10) -- I find it rather inconvenient and I can't really see any good reason to do that. In fact, it makes the usage of substring unsafe and the countermeasures I can imagine (manual bounds checks, padding, writing my-own-substring-function, whatever) are quite unsatisfactory... to me at least. If you prefer braindead bug-ridden do what I mean-ish behaviour of other, more sloppy languages, use PHP. Scheme is about correctness. If you provide invalid indices, you get errors. This will help you detect bugs early on instead of just keep going on with a bad result of an incorrect computation until some other thing fails much farther along. This kind of thing also tends to sneak in vulnerabilities, as you never *really* know what your code will do in the face of inconsistencies. fail early and noisily is good design. More seriously, if you think you know what you're doing and really want this kind of broken behaviour, we have an egg that emulates this kind of nonsense: http://wiki.call-cc.org/eggref/4/slice #;1 (use slice) #;2 (slice foo 0 10) foo Cheers, Peter -- http://sjamaan.ath.cx ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
Hi Michele, Michele La Monaca mikele.chic...@lamonaca.net writes: Maybe this is not the right list for that, sorry. yeah, this one probably better fits chicken-users as it's not really about Chicken's implementation, so you might be losing some broader audience by posting it here. No problemo, though! In fact, it makes the usage of substring unsafe and the countermeasures I can imagine (manual bounds checks, padding, writing my-own-substring-function, whatever) are quite unsatisfactory... to me at least. I felt the same when coming to Scheme (from Ruby in my case). But after having been immersed in the langauge and community surrounding it for a while now I came to see it in a different light: What might look like impracticality at the beginning turns out to be a virtue in its own right. All languages you cite (well, apart from Python perhaps, as Peter noted) are from the DWIM-most-of-the-time spectrum which give a lot of leeway. This often leads to what Olin Shivers vividly describes as 80% solutions in the preamble of the SRE announcement (see http://www.scsh.net/docu/post/sre.html). I recommend you to read that one if you don't already know it. Scheme as a whole tries to aim for the 100% solutions (whether it's successful in that endeavor is open for debate, of course). That's why you'll often see functions reduced to their bare minimum purpose and correct behavior even in edge cases. This is especially true for functions defined in the standard core such as the one you are referring to. The nice thing is that from that solid core as a foundation we can build libraries which allow us to be a bit more sloppy when we want to whereas it's much harder to go the other way around. It may sound a bit like just drink the Kool-Aid but what I'm trying to say is: Scheme, as any language, has its own culture and you will be much happier when you try to embrace it rather than trying to impose concepts from other languages on it. But you probably already know this, so I hope my comment on the specific case of your substring issue is of help, anyway :-) Moritz ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
# perl -e 'print substr(ciao,0,10);' ciao # ruby -e 'puts ciao[0..10]' ciao # python -c 'print ciao[0:10];' ciao # csi -e '(print (substring ciao 0 10))' Error: (substring) out of range 0 10 Call history: syntax (print (substring ciao 0 10)) syntax (substring ciao 0 10) eval(print (substring ciao 0 10)) eval(substring ciao 0 10) -- The string is shorter than the limit you gave to substring in the third argument. Of course you know that, but why did you pass an incorrect length in the first place? This looks like it does what you want: csi -e '(print (substring ciao 0))' cheers, felix ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
On Wed, Feb 6, 2013 at 12:18 AM, Jim Ursetto zbignie...@gmail.com wrote: On Feb 5, 2013, at 4:11 PM, Michele La Monaca wrote: Maybe this is not the right list for that, sorry. But is there a good reason for this [error on out-of-bounds substring access] behavior? I think it's along the lines of (cdr '()) being an error in Scheme instead of NIL as in Lisp. Jim Hi Peter, Morizt, Jim, thanks for your answers. What I can say... Well, maybe one day I will see the light, in the meanwhile I would just have preferred a more useful substring function. I really think that the one provided by chicken is simply not on par with other languages, sorry. The semantic of a commonly-found substring function give me at most N chars starting from a certain position in the string is the most useful according me. I don't see any evil in that. The chicken (scheme?) alternative give me exactly N chars or blow up is rather limited in scope to me. Scheme is about correctness. If you provide invalid indices, you get errors. Well, in the real world you can't always predict input and therefore you must do checks. Either you leave this burden to the user or you kindly provide this even-cobol-has-it feature. This will help you detect bugs early on instead of just keep going on with a bad result of an incorrect computation until some other thing fails much farther along. This kind of thing also tends to sneak in vulnerabilities, as you never *really* know what your code will do in the face of inconsistencies. fail early and noisily is good design. To me, this only means more bloated, unreadable code in the best case, unfriendly crashes in the worst one. Regards, Michele ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
Peter Bex scripsit: Scheme is about correctness. If you provide invalid indices, you get errors. This will help you detect bugs early on instead of just keep going on with a bad result of an incorrect computation until some other thing fails much farther along. This kind of thing also tends to sneak in vulnerabilities, as you never *really* know what your code will do in the face of inconsistencies. fail early and noisily is good design. In fact, R5RS and R7RS in no way require this kind of correctness. (substring foo 0 10) is the equivalent of a domain error at the value level, and both standards say that domain errors are up to the implementation to handle as they see fit. Chicken is definitely a safe implementation as most are, but unsafe ones that return foo in this case, or even crash, are entirely within the remit of the standards. (R6RS is a different matter, but Chicken doesn't do R6RS, and even implementations that do attempt compliance often aren't fully safe in their error behavior.) What Scheme is really about, if it has to be said to be about something, is implementation choice. Schemes provide and extend the language in different ways, and you pick the one that provides the levels of speed, safety, size, compilation speed, debuggability, or whatever other factors you want. -- Take two turkeys, one goose, four John Cowan cabbages, but no duck, and mix them http://www.ccil.org/~cowan together. After one taste, you'll duck co...@ccil.org soup the rest of your life. --Groucho ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
On Feb 5, 2013, at 5:55 PM, Michele La Monaca wrote: What I can say... Well, maybe one day I will see the light, in the meanwhile I would just have preferred a more useful substring function. I really think that the one provided by chicken is simply not on par with other languages, sorry. I'll get Sussman on the phone. The semantic of a commonly-found substring function give me at most N chars starting from a certain position in the string is the most useful according me. Well, your Perl example did that, but the Ruby, Python and Chicken ones all give you chars between START and END, not N chars from START. So you would have to write some shim code anyway. So while you're in there, just add a couple 'min' expressions. (define (substring/n s start n) (let* ((start (min start (string-length s))) (end (min (string-length s) (+ start n (substring s start end))) To me, this only means more bloated, unreadable code in the best case, unfriendly crashes in the worst one. (substring/n ciao 1 10) iao Presto, now your code isn't bloated, and you have up to N chars from START. Jim P.S. He sent me to voicemail. ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
On Feb 5, 2013, at 4:11 PM, Michele La Monaca wrote: Maybe this is not the right list for that, sorry. But is there a good reason for this [error on out-of-bounds substring access] behavior? I think it's along the lines of (cdr '()) being an error in Scheme instead of NIL as in Lisp. Jim ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
Michele La Monaca scripsit: The funny thing looking at the implementation is that it actually does the check (so no speed) only to have a better opportunity to crash (so no safety). Raising an exception is not crashing. Crashing means that no recovery is possible within the Scheme process, which is not the case here. -- Evolutionary psychology is the theory John Cowan that men are nothing but horn-dogs, http://www.ccil.org/~cowan and that women only want them for their money. co...@ccil.org --Susan McCarthy (adapted) ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
On Wed, Feb 06, 2013 at 12:10:09AM +0100, Moritz Heidkamp wrote: Hi Michele, Michele La Monaca mikele.chic...@lamonaca.net writes: Maybe this is not the right list for that, sorry. yeah, this one probably better fits chicken-users as it's not really about Chicken's implementation, so you might be losing some broader audience by posting it here. No problemo, though! In fact, it makes the usage of substring unsafe and the countermeasures I can imagine (manual bounds checks, padding, writing my-own-substring-function, whatever) are quite unsatisfactory... to me at least. I felt the same when coming to Scheme (from Ruby in my case). But after having been immersed in the langauge and community surrounding it for a while now I came to see it in a different light: What might look like impracticality at the beginning turns out to be a virtue in its own right. All languages you cite (well, apart from Python perhaps, as Peter noted) are from the DWIM-most-of-the-time spectrum which give a lot of leeway. This often leads to what Olin Shivers vividly describes as 80% solutions in the preamble of the SRE announcement (see http://www.scsh.net/docu/post/sre.html). I recommend you to read that one if you don't already know it. Scheme as a whole tries to aim for the 100% solutions (whether it's successful in that endeavor is open for debate, of course). That's why you'll often see functions reduced to their bare minimum purpose and correct behavior even in edge cases. This is especially true for functions defined in the standard core such as the one you are referring to. The nice thing is that from that solid core as a foundation we can build libraries which allow us to be a bit more sloppy when we want to whereas it's much harder to go the other way around. It may sound a bit like just drink the Kool-Aid but what I'm trying to say is: Scheme, as any language, has its own culture and you will be much happier when you try to embrace it rather than trying to impose concepts from other languages on it. But you probably already know this, so I hope my comment on the specific case of your substring issue is of help, anyway :-) Moritz I certainly appreciate this design principle, but there is just no explaining DSSSL using the above philosophy. I find the interaction between #!rest and #!key much more sensible in Python, which forbids every potentially ambiguous case and therefor has much more consistent behavior with the various combinations available. -Alan -- my personal website: http://c0redump.org/ ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
.alyn.post. scripsit: I certainly appreciate this design principle, but there is just no explaining DSSSL using the above philosophy. I find the interaction between #!rest and #!key much more sensible in Python, which forbids every potentially ambiguous case and therefor has much more consistent behavior with the various combinations available. DSSSL was cloning Common Lisp here, and Common Lisp has never given a single, double, short, or long damn for consistency. -- John Cowan co...@ccil.org http://www.ccil.org/~cowan .e'osai ko sarji la lojban. Please support Lojban! http://www.lojban.org ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
Michele La Monaca scripsit: I never read them (I promise I'll do, at least R5RS) but I was kind of suspecting that no standard would ever tell you if the input is such or such... then crash!. Well, no. But certainly the C and C++ standards, for example, give *permission* to crash by using the phrase undefined behavior. In R6RS, it's the opposite story: essentially all behaviors are defined, either to produce a certain result or to raise an exception of a certain type, both of which the user can rely on. The way it is, is the chicken way not the scheme way. To be fair, it is also the way of the great majority of Scheme implementations. And most Scheme systems are quite strict, simply because it's easier to build lax code on top of strict code than the other way around. Given Scheme's extreme extensibility of both syntax and procedures, this is perfectly reasonable: if you want lax behavior, import a lax library instead of the base (strict) library. -- John Cowanco...@ccil.orghttp://ccil.org/~cowan Half the lies they tell about me are true. --Tallulah Bankhead, American actress ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
Re: [Chicken-hackers] substring function and bounds checks
On Wed, Feb 6, 2013 at 1:35 AM, John Cowan co...@mercury.ccil.org wrote: What Scheme is really about, if it has to be said to be about something, is implementation choice. Schemes provide and extend the language in different ways, and you pick the one that provides the levels of speed, safety, size, compilation speed, debuggability, or whatever other factors you want. The funny thing looking at the implementation is that it actually does the check (so no speed) only to have a better opportunity to crash (so no safety). Regards, Michele ___ Chicken-hackers mailing list Chicken-hackers@nongnu.org https://lists.nongnu.org/mailman/listinfo/chicken-hackers
