8 ms·

> perhaps writing if 5 < x and x < 100 instead of the much clearer if 5 < $x < 100 Why not "if 5 < x < 100"? Sigils look awful.

by Grue3 11y ago

true_religion 11y ago
I think sigils in Perl 6 denote variable scope at a glance; so you don't have to write self.X everywhere. Also you get to know if a variable is only block scope, method scope, class variable, etc.
- awwaiid 11y ago
  Sigils in Perl 6 are rough type constraints on their content. More specifically, the indicate a Role. $x is unconstrained, @x does the Positional role, %x does the Associative role, &x does Callable. Twigils in Perl 6 are where the scope indicators come in, clarifying class instance vars, dynamic scope, and so on. So if I see %.foo I can tell you that this variable can be used as the Associative role, that it is scoped as an instance variable, and that it has an accessor with the same name. For more, see the first few sections of http://doc.perl6.org/language/variables http://doc.perl6.org/language/variables
hahainternet 11y ago
> Why not "if 5 < x < 100"? Sigils look awful. Because sigils tell you things. What if 'x' in your example is a list? Are you now checking the length of the list rather than the value? Sounds like room for a security bug to me.
- lmm 11y ago
  > Because sigils tell you things. What if 'x' in your example is a list? Are you now checking the length of the list rather than the value? Sounds like room for a security bug to me. Only if your language is really awful. A good language shouldn't even let you run "5 < x" when x is a list, but even a mediocre one would surely at least make that error out at runtime rather than giving a nonsense answer.
  - hahainternet 11y ago
    > Only if your language is really awful. A good language shouldn't even let you run "5 < x" when x is a list, but even a mediocre one would surely at least make that error out at runtime rather than giving a nonsense answer. It depends what you consider "Nonsense". Python for example has no reliable way to differentiate between a string and a list. Strings are iterable, but lists can't be compared with the < syntax for example. My point is simply that $x very clearly says (in Perl 6) "A single value called x" wheras @x is "A list of values called x". In python, "x" is indeterminate even at runtime. Oh, and you can declare barewords with \x for example, if you really want to, it is Perl after all.
    - DonHopkins 11y ago
      What version of Python can't differentiate between a string and a list, or compare lists? Python 2.7.10 (default, Jun 10 2015, 19:42:47) [GCC 4.2.1 Compatible Apple LLVM 6.1.0 (clang-602.0.53)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> type([1]) <type 'list'> >>> type('1') <type 'str'> >>> type(1) == type('1') False >>> [1] < [2] True >>> [2] < [1] False >>> I consider it "Nonsense" to abuse overloaded context sensitive strings of punctuation with arbitrary rules of precedence and associativity, instead of English words correctly spelled out of letters that people can look up alphabetically in a reference manual and google for tutorials to find out what they mean.
      - hahainternet 11y ago
        Sorry I should have made things more clear. I am talking about in things like function signatures. Doing something like isinstance(x, str) is discouraged and considered non-pythonic, and recently hasattr() has also been talked about. However, both strings and lists can be iterated, so assuming that this will fail is incorrect: x = "Hello" for y in x: print("{} is {}".format(y, type(y))) I asked on IRC and ultimately the only answer I got was that the most pythonic way to do things was to name functions whatever_str and whatever_list. edit: I also should have said above "lists can't be compared with strings using <". I was trying to point out Python did things potentially correctly there, but I see now it's ambiguous.
- Grue3 11y ago
  In other languages this is solved by naming variables appropriately. There would be no variable "x" because it's a bad name. It would be something like coefficient-of-friction which is clearly a scalar. Having to write a symbol to denote that it's a scalar is superfluous. This explains why Perl code looks so messy, by the way. The language itself encourages poor variable naming.
  - hahainternet 11y ago
    Really? my %clients vs my @clients Do you name your variables client_list .. client_dictionary? No? Then sigils aren't superfluous.
    - slavik81 11y ago
      Well, yes. When I use a list, I name them clients. When I use a hash, I specify the key. For example, clientsById.
      - hahainternet 11y ago
        With a language like Perl 6, you can happily use simply @clients or %clients and if you define those correctly, you can explicitly detail the key too.
  - kbenson 11y ago
    As long as you view Perl, whether 5 or 6, in the light of C and assume it should function like C, then there will be lots of little things that seem odd and pointless. When you accept that Perl implements some things that C has no concept of whatsoever, and uses them to it's advantage throughout the language, then many of these little things start to make sense. Specifically, Perl uses context to change behavior, and lists behave differently depending on context. This is really no different than how Lisp uses parenthesis in a different way than C, except that Lisp has the benefit of being more visually distinct so people that are familiar with C and C-like semantics don't immediately assume they know what's going on an why when they see Lisp constructs. Perl is different as well, but it often looks similar enough to cause people concern before they know what they are really looking at. As for this specific example, arrays evaluated in scalar context (as opposed to list context) return the number of elements in the array. There is no array length function or method, as it's superfluous. 0+@x is the number of items in @x, and 5 < @x tests whether @x has more than 5 items, since < imposes scalar context. There are many, many places in the language where context is used to simplify operations, this is just a very simplistic example, but it should illustrate why sigils are important, as they change how operations are evaluated. Put simply, it's not possible to make a coherent criticism of Perl's use of sigils without understanding context and how it's used within the language, and factoring the benefits and drawbacks of that into your criticism. To criticize without this knowledge is to do so from ignorance (in the literal sense, not as an insult).

> perhaps writing if 5 < x and x < 100 instead of the much clearer if 5 < $x < 100 Why not "if 5 < x < 100"? Sigils look awful.

by Grue3 11y ago

> perhaps writing if 5 < x and x < 100 instead of the much clearer if 5 < $x < 100 Why not "if 5 < x < 100"? Sigils look awful.

true_religion 11y ago

I think sigils in Perl 6 denote variable scope at a glance; so you don't have to write self.X everywhere. Also you get to know if a variable is only block scope, method scope, class variable, etc.

awwaiid 11y ago
Sigils in Perl 6 are rough type constraints on their content. More specifically, the indicate a Role. $x is unconstrained, @x does the Positional role, %x does the Associative role, &x does Callable. Twigils in Perl 6 are where the scope indicators come in, clarifying class instance vars, dynamic scope, and so on. So if I see %.foo I can tell you that this variable can be used as the Associative role, that it is scoped as an instance variable, and that it has an accessor with the same name. For more, see the first few sections of http://doc.perl6.org/language/variables http://doc.perl6.org/language/variables

hahainternet 11y ago

> Why not "if 5 < x < 100"? Sigils look awful. Because sigils tell you things. What if 'x' in your example is a list? Are you now checking the length of the list rather than the value? Sounds like room for a security bug to me.

lmm 11y ago
> Because sigils tell you things. What if 'x' in your example is a list? Are you now checking the length of the list rather than the value? Sounds like room for a security bug to me. Only if your language is really awful. A good language shouldn't even let you run "5 < x" when x is a list, but even a mediocre one would surely at least make that error out at runtime rather than giving a nonsense answer.
- hahainternet 11y ago
  > Only if your language is really awful. A good language shouldn't even let you run "5 < x" when x is a list, but even a mediocre one would surely at least make that error out at runtime rather than giving a nonsense answer. It depends what you consider "Nonsense". Python for example has no reliable way to differentiate between a string and a list. Strings are iterable, but lists can't be compared with the < syntax for example. My point is simply that $x very clearly says (in Perl 6) "A single value called x" wheras @x is "A list of values called x". In python, "x" is indeterminate even at runtime. Oh, and you can declare barewords with \x for example, if you really want to, it is Perl after all.
  - DonHopkins 11y ago
    What version of Python can't differentiate between a string and a list, or compare lists? Python 2.7.10 (default, Jun 10 2015, 19:42:47) [GCC 4.2.1 Compatible Apple LLVM 6.1.0 (clang-602.0.53)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> type([1]) <type 'list'> >>> type('1') <type 'str'> >>> type(1) == type('1') False >>> [1] < [2] True >>> [2] < [1] False >>> I consider it "Nonsense" to abuse overloaded context sensitive strings of punctuation with arbitrary rules of precedence and associativity, instead of English words correctly spelled out of letters that people can look up alphabetically in a reference manual and google for tutorials to find out what they mean.
    - hahainternet 11y ago
      Sorry I should have made things more clear. I am talking about in things like function signatures. Doing something like isinstance(x, str) is discouraged and considered non-pythonic, and recently hasattr() has also been talked about. However, both strings and lists can be iterated, so assuming that this will fail is incorrect: x = "Hello" for y in x: print("{} is {}".format(y, type(y))) I asked on IRC and ultimately the only answer I got was that the most pythonic way to do things was to name functions whatever_str and whatever_list. edit: I also should have said above "lists can't be compared with strings using <". I was trying to point out Python did things potentially correctly there, but I see now it's ambiguous.
Grue3 11y ago
In other languages this is solved by naming variables appropriately. There would be no variable "x" because it's a bad name. It would be something like coefficient-of-friction which is clearly a scalar. Having to write a symbol to denote that it's a scalar is superfluous. This explains why Perl code looks so messy, by the way. The language itself encourages poor variable naming.
- hahainternet 11y ago
  Really? my %clients vs my @clients Do you name your variables client_list .. client_dictionary? No? Then sigils aren't superfluous.
  - slavik81 11y ago
    Well, yes. When I use a list, I name them clients. When I use a hash, I specify the key. For example, clientsById.
    - hahainternet 11y ago
      With a language like Perl 6, you can happily use simply @clients or %clients and if you define those correctly, you can explicitly detail the key too.
- kbenson 11y ago
  As long as you view Perl, whether 5 or 6, in the light of C and assume it should function like C, then there will be lots of little things that seem odd and pointless. When you accept that Perl implements some things that C has no concept of whatsoever, and uses them to it's advantage throughout the language, then many of these little things start to make sense. Specifically, Perl uses context to change behavior, and lists behave differently depending on context. This is really no different than how Lisp uses parenthesis in a different way than C, except that Lisp has the benefit of being more visually distinct so people that are familiar with C and C-like semantics don't immediately assume they know what's going on an why when they see Lisp constructs. Perl is different as well, but it often looks similar enough to cause people concern before they know what they are really looking at. As for this specific example, arrays evaluated in scalar context (as opposed to list context) return the number of elements in the array. There is no array length function or method, as it's superfluous. 0+@x is the number of items in @x, and 5 < @x tests whether @x has more than 5 items, since < imposes scalar context. There are many, many places in the language where context is used to simplify operations, this is just a very simplistic example, but it should illustrate why sigils are important, as they change how operations are evaluated. Put simply, it's not possible to make a coherent criticism of Perl's use of sigils without understanding context and how it's used within the language, and factoring the benefits and drawbacks of that into your criticism. To criticize without this knowledge is to do so from ignorance (in the literal sense, not as an insult).