Re: Tuple literal syntax + Tuple assignment
On 07/10/2010 19:45, Andrei Alexandrescu wrote: On 10/7/10 12:45 CDT, Michel Fortin wrote: On 2010-10-07 12:34:33 -0400, Andrei Alexandrescu said: My suggestion is that we deprecate TypeTuple and we call it AliasTuple because that's really what it is - it's a tuple of stuff that can be passed in as an alias parameter. Personally, I like D built-in tuples; they're so simple. At the core they're just a group of "things". They are terrible, awful, despiteful. They don't compose with anything; you can't have an array of tuples or a hash of tuples. They can't be returned a from a function. They spread their legs in function parameter lists without any control (flattening is bad, right?) Built-in tuples are the pitts. The one thing they're good for is as a back-end for std.typecons.Tuple. In fairness, my impression is they were not meant to compose with anything or be returned with a function. They were created not as a first class type, but as a metaprogramming construct, whose purpose was *exactly* for capturing parameters for templates or functions and expanding them automatically. They were a great boon for D's metaprogramming capabilities. As such they were not meant to emulate tuples as in Python's tuples, or any record type in general. But because they could partially be used as such, and because they share the same name, a lot of comparisons are made, which results in this idea that D's tuples are inferior. This is not saying it would not be useful to have functionality like Python's tuples. -- Bruno Medeiros - Software Engineer
Re: Tuple literal syntax + Tuple assignment
In the two threads (that are a single thread) most of the things I've seen are bad/wrong. I have discussed about Tuples several times in the D newsgroup and in Bugzilla. Please don't ignore all my work. Before designing tuple syntax you must decide what the purpose of D tuples is. Then you have to solve the design problems, and avoid all (or most) corner cases. In this discussion it's useful to have a certain experience of languages that use tuples often, as Python and others. Tuples have some purposes: - Python, Go and other languages show that it's handy to allow functions to return multiple values, this means a tuple. - A handy tuple unpacking is useful at the calling point of a function that returns multiple return values. - Tuples are also useful as quick-and-dirty structs, to sort items in a different order, etc. It's useful to use [] to access tuple items, to slice tuples, concat them. It's useful for tuples to have a good textual representation, to be comparable lexicographically and to be hashable. Another design decision is if tuples have a nominative or structural type, this problem comes out in this bug report: http://d.puremagic.com/issues/show_bug.cgi?id=4128 In my opinion it's good for a built-in D tuple to be a structural type. This also means you are allowed to perform an == among two tuples of different length (the result is known statically to be always false). I assume that D tuples know their length at compile-time. Another significant problem is about naming things, currently the situation is a mess: http://www.digitalmars.com/d/archives/digitalmars/D/Tuple_TypeTuple_tupleof_etc_113005.html http://d.puremagic.com/issues/show_bug.cgi?id=4113 In the end I have suggested to name "record" the typecons tuples, and "tuple" the typetuples. I have several bug reports and enhancement requests about tuples, please take them into account: http://d.puremagic.com/issues/show_bug.cgi?id=4577 http://d.puremagic.com/issues/show_bug.cgi?id=4582 http://d.puremagic.com/issues/show_bug.cgi?id=4591 http://d.puremagic.com/issues/show_bug.cgi?id=4666 http://d.puremagic.com/issues/show_bug.cgi?id=4846 Walter: > A lot of it foundered on what the syntax for tuple literals should be. The top > of the list is simply enclosing them in ( ). This is a bad idea. It has caused troubles in Python because of the singleton syntax (tuple with 1 item). One solution is to use a special unambigous delimiter to denote tuples, like (a similar solution is used in the Fortress language): (||) (|1|) (|1, 2|) (|1, 2, 3|) (|1, 2, 3, 4|) Otherwise a good solution is to use a name: record() record(1) record(1, 2) record(1, 2, 3) record(1, 2, 3, 4) I prefer the record() solution, but the first solution too acceptable. > Finally, I got to thinking, why not just make it a special case: > > ( ) == tuple > (a) == parenthesized expression This is not acceptable. No special cases, please. D has already a ton of special cases. Python solves this with the (1,) syntax, but it's not nice, it's error-prone, and it confuses newbies. > If expr represents a tuple, we (Andrei and I) were thinking about the syntax: > > auto (a, b, c, d) = expr; On this topic I have this enhancement request: http://d.puremagic.com/issues/show_bug.cgi?id=4579 > The Lithpers among you will notice that this essentially provides a handy > car,cdr shortcut for tuples and arrays: > > auto (car, cdr) = expr; This is bad, it's not explicit enough. If you want to support this semantics then the syntax has to show what you mean. Python uses a * to denote "grab the whole tail". In D you may use something else, others have suggested tree points, this works with dynamic arrays too: auto (car, cdr...) = expr; Regarding field names for tuples, I have used Python and I like the optional names of D tuples (records). In some situations you don't need names, but in other situations field names are handy and help avoid bugs. In Python code that processes and uses tuples contains too many [0] [1] [2] etc that aren't readable and are bug-prone. But a good management of such names asks for the names to not change the type of the tuple, this is why I talk about structural typing for records. Bye, bearophile
Re: Tuple literal syntax + Tuple assignment
bearophile wrote: In my opinion it's good for a built-in D tuple to be a structural type. This also means you are allowed to perform an == among two tuples of different length (the result is known statically to be always false). I understand (and agree to) the opinion that tuples should be structural types, but why allow comparison of tuples of different lengths? Walter: A lot of it foundered on what the syntax for tuple literals should be. The top of the list is simply enclosing them in ( ). This is a bad idea. It has caused troubles in Python because of the singleton syntax (tuple with 1 item). One solution is to use a special unambigous delimiter to denote tuples, like (a similar solution is used in the Fortress language): (|1, 2, 3, 4|) Otherwise a good solution is to use a name: record(1, 2, 3, 4) I prefer the record() solution, but the first solution too acceptable. Yeah, ( T... ) is not a good general tuple syntax. I believe auto( ) is a free syntax in D, and thus could be used for tuples. Thinking more about it, I am no longer as sure. auto (car, cdr...) = expr; I really like this. Regarding field names for tuples, I have used Python and I like the optional names of D tuples (records). In some situations you don't need names, but in other situations field names are handy and help avoid bugs. In Python code that processes and uses tuples contains too many [0] [1] [2] etc that aren't readable and are bug-prone. But a good management of such names asks for the names to not change the type of the tuple, this is why I talk about structural typing for records. I wrote a Tuple implementation for D that supports structural typing: http://pastebin.com/qeYKa5GZ (see line 58-60 for proof) This is a simple proof-of-concept, so don't expect anything impressive from it. -- Simen
Re: Tuple literal syntax + Tuple assignment
On 10/7/10 7:09 CDT, bearophile wrote: In the two threads (that are a single thread) most of the things I've seen are bad/wrong. I have discussed about Tuples several times in the D newsgroup and in Bugzilla. Please don't ignore all my work. Before designing tuple syntax you must decide what the purpose of D tuples is. Then you have to solve the design problems, and avoid all (or most) corner cases. In this discussion it's useful to have a certain experience of languages that use tuples often, as Python and others. Good point. Tuples have some purposes: - Python, Go and other languages show that it's handy to allow functions to return multiple values, this means a tuple. - A handy tuple unpacking is useful at the calling point of a function that returns multiple return values. - Tuples are also useful as quick-and-dirty structs, to sort items in a different order, etc. It's useful to use [] to access tuple items, to slice tuples, concat them. It's useful for tuples to have a good textual representation, to be comparable lexicographically and to be hashable. Yes, excellent. Now I realize we don't have hash for tuples just yet. Another design decision is if tuples have a nominative or structural type, this problem comes out in this bug report: http://d.puremagic.com/issues/show_bug.cgi?id=4128 In my opinion it's good for a built-in D tuple to be a structural type. This also means you are allowed to perform an == among two tuples of different length (the result is known statically to be always false). I assume that D tuples know their length at compile-time. Yah, I think tuples are the quintessential structural types. I think, however, that "==" shouldn't test for prefix (that would be _sub_typing). This is because slicing takes care of it. For example: Tuple!(int, int, int) point3d; Tuple!(int, int) point2d; point2d == point3d; // doesn't compile point2d == point3d[0 .. point2d.length]; // compiles Another significant problem is about naming things, currently the situation is a mess: http://www.digitalmars.com/d/archives/digitalmars/D/Tuple_TypeTuple_tupleof_etc_113005.html http://d.puremagic.com/issues/show_bug.cgi?id=4113 In the end I have suggested to name "record" the typecons tuples, and "tuple" the typetuples. I think we're in good shape with Tuple and tuple. The "other" tuples deserve an odder name. I have several bug reports and enhancement requests about tuples, please take them into account: http://d.puremagic.com/issues/show_bug.cgi?id=4577 http://d.puremagic.com/issues/show_bug.cgi?id=4582 http://d.puremagic.com/issues/show_bug.cgi?id=4591 http://d.puremagic.com/issues/show_bug.cgi?id=4666 http://d.puremagic.com/issues/show_bug.cgi?id=4846 Nice. I like at least some of each. Walter: A lot of it foundered on what the syntax for tuple literals should be. The top of the list is simply enclosing them in ( ). This is a bad idea. It has caused troubles in Python because of the singleton syntax (tuple with 1 item). During our conversation I conveyed my suspicion that that one corner case (which is very often encountered in generic code) will inevitably do this whole thing in, but he was quick to gloss over the issues. I'd be glad to have experience with Python save us some sweat. Do you have any links to discussions regarding the matter? One solution is to use a special unambigous delimiter to denote tuples, like (a similar solution is used in the Fortress language): (||) (|1|) (|1, 2|) (|1, 2, 3|) (|1, 2, 3, 4|) Yup, the banana notation. Otherwise a good solution is to use a name: record() record(1) record(1, 2) record(1, 2, 3) record(1, 2, 3, 4) I prefer the record() solution, but the first solution too acceptable. How about the shorter "tuple"? Wait, it's already there :o). Finally, I got to thinking, why not just make it a special case: ( ) == tuple (a) == parenthesized expression This is not acceptable. No special cases, please. D has already a ton of special cases. Python solves this with the (1,) syntax, but it's not nice, it's error-prone, and it confuses newbies. Evidence please? If expr represents a tuple, we (Andrei and I) were thinking about the syntax: auto (a, b, c, d) = expr; On this topic I have this enhancement request: http://d.puremagic.com/issues/show_bug.cgi?id=4579 The Lithpers among you will notice that this essentially provides a handy car,cdr shortcut for tuples and arrays: auto (car, cdr) = expr; This is bad, it's not explicit enough. If you want to support this semantics then the syntax has to show what you mean. Python uses a * to denote "grab the whole tail". In D you may use something else, others have suggested tree points, this works with dynamic arrays too: auto (car, cdr...) = expr; Nice. Regarding field names for tuples, I have used Python and I like the optional names of D tuples (records). In some situations you don't need names, but in other situ
Re: Tuple literal syntax + Tuple assignment
2010/10/7 bearophile : > Another design decision is if tuples have a nominative or structural type, > this problem comes out in this bug report: > http://d.puremagic.com/issues/show_bug.cgi?id=4128 > Another significant problem is about naming things, currently the situation > is a mess: > http://www.digitalmars.com/d/archives/digitalmars/D/Tuple_TypeTuple_tupleof_etc_113005.html > http://d.puremagic.com/issues/show_bug.cgi?id=4113 > In the end I have suggested to name "record" the typecons tuples, and "tuple" > the typetuples. On these issues, I'm almost agreed with bearophile I think we may not use 'Tuple' as 'a structure packed values'. It is more better that 'Tuple' should *only* use as mixing sequence types and values. My proposals are: 1. We should name definitions of structures. - "Structure that all of fields have name" shuld be called 'Struct'. - "Structure that some of fields have name" shuld be called 'Odd struct'. - "Structure that none of fields have name" shuld be called 'Record'. Struct∈Odd struct∈Record 2. We remove field namming funcion from std.typecons.tuple, and rename it to Record. 3. We rename std.typetuple.TypeTuple to Tuple. pseudo codes: auto a = Record!(int, int)(10, 20); auto b = Struct!(int, "x", int, "y")(100, 200); //a = b; //should not compile, named field(x, y) cannot assign to unnamed field b = a; //should compile, unnamed field can assign to named field assert(b[0] == 10); assert(b[1] == 20); auto c = OddStruct!(int, "x", int)(15, 25); //a = c; //shuld not compile, named field(x) cannot assign to unnamed field b = c; //shuld compile assert(b[0] == 15); assert(b[1] == 25); c = a; //shuld compile assert(c[0] == 10); assert(c[1] == 20); thanks. Kenji Hara.
Re: Tuple literal syntax + Tuple assignment
On 10/7/10 11:11 CDT, kenji hara wrote:
> 2010/10/7 bearophile:
>> Another design decision is if tuples have a nominative or structural type,
>> this problem comes out in this bug report:
>> http://d.puremagic.com/issues/show_bug.cgi?id=4128
>
>> Another significant problem is about naming things, currently the situation
>> is a mess:
>> http://www.digitalmars.com/d/archives/digitalmars/D/Tuple_TypeTuple_tupleof_etc_113005.html
>> http://d.puremagic.com/issues/show_bug.cgi?id=4113
>> In the end I have suggested to name "record" the typecons tuples, and
>> "tuple" the typetuples.
>
> On these issues, I'm almost agreed with bearophile
>
> I think we may not use 'Tuple' as 'a structure packed values'.
> It is more better that 'Tuple' should *only* use as mixing sequence
> types and values.
The problem with this is that it departs from nomenclature that is
agreed by everyone else, which is provincial.
First off, a tuple IS agreed to be an ordered collection of
heterogeneous items. Google reveals copious evidence, both in math and
programming language theory.
Benjamin Pierce's "Types and programming languages", a book that all PL
students sleep with under their pillow, defines tuples in section 11.7
(entitled "Tuples") like D does. The first paragraph:
"It is easy to generalize the binary products of the previous section to
n-ary products, often called tuples. For example, {1,2,true} is a
3-tuple containing two numbers and a Boolean. Its type is written
{Nat,Nat,Bool}."
The following section defines records as tuples with labeled fields. I
don't think it's a crime that D calls both tuples. We could define
Record just to be more Catholic than the Pope, but I don't see a
necessity there. At any rate, "Tuple" is correct, known, understood, and
accepted.
D's built in type tuples (those used with TypeTuple) are weird. They are
an artifact of the language that has no meaning outside it. Such tuples
are defined as "anything that could be a template parameter", which
really ties them to various language design decisions. My suggestion is
that we deprecate TypeTuple and we call it AliasTuple because that's
really what it is - it's a tuple of stuff that can be passed in as an
alias parameter.
> My proposals are:
> 1. We should name definitions of structures.
> - "Structure that all of fields have name" shuld be called 'Struct'.
> - "Structure that some of fields have name" shuld be called 'Odd struct'.
> - "Structure that none of fields have name" shuld be called 'Record'.
>
> Struct∈Odd struct∈Record
>
> 2. We remove field namming funcion from std.typecons.tuple, and rename
> it to Record.
>
> 3. We rename std.typetuple.TypeTuple to Tuple.
>
>
> pseudo codes:
>
> auto a = Record!(int, int)(10, 20);
This is not a record by Pierce.
> auto b = Struct!(int, "x", int, "y")(100, 200);
This is a record by Pierce.
> auto c = OddStruct!(int, "x", int)(15, 25);
We could reject this during compilation if needed.
I don't see anything confusing grouping the above under "Tuple".
Andrei
Re: Tuple literal syntax + Tuple assignment
2010年10月8日1:34 Andrei Alexandrescu :
> On 10/7/10 11:11 CDT, kenji hara wrote:
>> 2010/10/7 bearophile:
>>> Another design decision is if tuples have a nominative or structural type,
>>> this problem comes out in this bug report:
>>> http://d.puremagic.com/issues/show_bug.cgi?id=4128
>>
>>> Another significant problem is about naming things, currently the situation
>>> is a mess:
>>> http://www.digitalmars.com/d/archives/digitalmars/D/Tuple_TypeTuple_tupleof_etc_113005.html
>>> http://d.puremagic.com/issues/show_bug.cgi?id=4113
>>> In the end I have suggested to name "record" the typecons tuples, and
>>> "tuple" the typetuples.
>>
>> On these issues, I'm almost agreed with bearophile
>>
>> I think we may not use 'Tuple' as 'a structure packed values'.
>> It is more better that 'Tuple' should *only* use as mixing sequence
>> types and values.
>
> The problem with this is that it departs from nomenclature that is
> agreed by everyone else, which is provincial.
>
> First off, a tuple IS agreed to be an ordered collection of
> heterogeneous items. Google reveals copious evidence, both in math and
> programming language theory.
>
> Benjamin Pierce's "Types and programming languages", a book that all PL
> students sleep with under their pillow, defines tuples in section 11.7
> (entitled "Tuples") like D does. The first paragraph:
>
> "It is easy to generalize the binary products of the previous section to
> n-ary products, often called tuples. For example, {1,2,true} is a
> 3-tuple containing two numbers and a Boolean. Its type is written
> {Nat,Nat,Bool}."
>
> The following section defines records as tuples with labeled fields. I
> don't think it's a crime that D calls both tuples. We could define
> Record just to be more Catholic than the Pope, but I don't see a
> necessity there. At any rate, "Tuple" is correct, known, understood, and
> accepted.
I understood that 'Tuple' is a generic word in math/language theory.
Withdraw my proposals.
> D's built in type tuples (those used with TypeTuple) are weird. They are
> an artifact of the language that has no meaning outside it. Such tuples
> are defined as "anything that could be a template parameter", which
> really ties them to various language design decisions. My suggestion is
> that we deprecate TypeTuple and we call it AliasTuple because that's
> really what it is - it's a tuple of stuff that can be passed in as an
> alias parameter.
It sounds for me that AliasTuple is a limited tuple contains only
alias parameters(exclude types).
I associate three kinds of template parameter (Type, Value, Alias)
with names '{Type|Value|Alias}Tuple'.
So I hope it will be called 'Tuple' in library, too.
(Given these, can I call std.typecons.Tuple ValueTyple?)
Thanks for your answer.
Kenji Hara
Re: Tuple literal syntax + Tuple assignment
On 2010-10-07 12:34:33 -0400, Andrei Alexandrescu said: My suggestion is that we deprecate TypeTuple and we call it AliasTuple because that's really what it is - it's a tuple of stuff that can be passed in as an alias parameter. Personally, I like D built-in tuples; they're so simple. At the core they're just a group of "things". If you put only types in the tuple then it becomes usable as a type, and if you put only values in the tuple then it becomes usable as a value, and if I put variable declarations in the tuple then it becomes usable as a single variable aliased to all those variables, and if I mix all kind of things then it's just a heterogenous tuple that's probably only suitable as a template parameter. Why should I know beforehand if I'm defining an alias tuple, a type tuple, a value tuple, or a whatever tuple? Seriously, the tuple is just a group of those "things" I put in it, and the compiler will tell me whenever I try to put that tuple where it doesn't belong. Now, it sure would make sense to have a way to enforce whether a tuple is valid as a type or a valid as a value. But for many uses it isn't necessary, and it does simplify things to not have to care about it. -- Michel Fortin michel.for...@michelf.com http://michelf.com/
Re: Tuple literal syntax + Tuple assignment
Thu, 07 Oct 2010 13:45:16 -0400, Michel Fortin wrote: > On 2010-10-07 12:34:33 -0400, Andrei Alexandrescu > said: > >> My suggestion is that we deprecate TypeTuple and we call it AliasTuple >> because that's really what it is - it's a tuple of stuff that can be >> passed in as an alias parameter. > > Personally, I like D built-in tuples; they're so simple. At the core > they're just a group of "things". If you put only types in the tuple > then it becomes usable as a type, and if you put only values in the > tuple then it becomes usable as a value, and if I put variable > declarations in the tuple then it becomes usable as a single variable > aliased to all those variables, and if I mix all kind of things then > it's just a heterogenous tuple that's probably only suitable as a > template parameter. > > Why should I know beforehand if I'm defining an alias tuple, a type > tuple, a value tuple, or a whatever tuple? Seriously, the tuple is just > a group of those "things" I put in it, and the compiler will tell me > whenever I try to put that tuple where it doesn't belong. > > Now, it sure would make sense to have a way to enforce whether a tuple > is valid as a type or a valid as a value. But for many uses it isn't > necessary, and it does simplify things to not have to care about it. We were discussing the semantics of the language. You can't design languages & compilers by just saying "do it the simple way, it should just work". The tuples & proposals are already combining several different features: tuples, records, arrays (slices & indexing), varargs, type definitions (type tuples), dependent types, pattern matching, nominative & structural typing, and ad-hoc features (.tupleof which.. in fact isn't any of the three listed tuples). On top of that there are syntactical conflicts. How is that in any possible way simple?
Re: Tuple literal syntax + Tuple assignment
On 10/7/10 12:45 CDT, Michel Fortin wrote: On 2010-10-07 12:34:33 -0400, Andrei Alexandrescu said: My suggestion is that we deprecate TypeTuple and we call it AliasTuple because that's really what it is - it's a tuple of stuff that can be passed in as an alias parameter. Personally, I like D built-in tuples; they're so simple. At the core they're just a group of "things". They are terrible, awful, despiteful. They don't compose with anything; you can't have an array of tuples or a hash of tuples. They can't be returned a from a function. They spread their legs in function parameter lists without any control (flattening is bad, right?) Built-in tuples are the pitts. The one thing they're good for is as a back-end for std.typecons.Tuple. If you put only types in the tuple then it becomes usable as a type, and if you put only values in the tuple then it becomes usable as a value, and if I put variable declarations in the tuple then it becomes usable as a single variable aliased to all those variables, and if I mix all kind of things then it's just a heterogenous tuple that's probably only suitable as a template parameter. Only a fraction of that is true. A tuple is not usable as a value. Andrei
Re: Tuple literal syntax + Tuple assignment
kenji hara: > My proposals are: > 1. We should name definitions of structures. > - "Structure that all of fields have name" shuld be called 'Struct'. > - "Structure that some of fields have name" shuld be called 'Odd struct'. > - "Structure that none of fields have name" shuld be called 'Record'. We already have structs, TypeTuples and Tuples, I'd like to reduce them to 2 types, not extend them to 4 :-) Bye, bearophile
Re: Tuple literal syntax + Tuple assignment
Andrei:
Another possible useful feature for tuples is to unpack them in foreach too:
import std.algorithm, std.stdio, std.range;
void main() {
foreach (p; zip([1, 2, 3], "abcd"))
writeln(p[0], " ", p[1]);
writeln();
foreach ((a, b); zip([1, 2, 3], "abcd"))
writeln(a, " ", b);
}
A related handy feature, present in Python2 is destructuring (unpacking) in
function signature:
- upacking syntax, pattern matching
>>> def foo((x, y), z): print y
...
>>> foo("ab", 2)
b
This allows you to do many things, like define a lambda function that swaps
items of the given 2-tuple:
lambda (seq,freq): (freq,seq)
Python3 has removed this automatic unpacking (not because that feature is not
handy, but mostly to simplify the source code of CPython!), and it has added
the unpaking syntax for n items:
first, second, *tail = (1, 2, 3, 4)
Recently I have written something about support for slicing tuples and similar
compile-time sized structures:
http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=117890
>I think, however, that "==" shouldn't test for prefix<
You are right, that's an error of mine caused by thinking about tuple lengths
as immutable but known at run-time only, as in Python. It's better to disallow
at compile time the opEquals of tuples of different length.
>I think we're in good shape with Tuple and tuple. The "other" tuples deserve
>an odder name.<
I don't love the name "record" and I agree that "tuple" is OK. But if in the
language there is a built-in attribute named "tupleof" that returns something
that's not a tuple, then... it's not nice. This is why I have suggested to name
tuples the built-in ones and record() the library+SyntaxSugar defined ones.
Naming them record is not terrible, in my opinion.
>During our conversation I conveyed my suspicion that that one corner case
>(which is very often encountered in generic code) will inevitably do this
>whole thing in, but he was quick to gloss over the issues. I'd be glad to have
>experience with Python save us some sweat. Do you have any links to
>discussions regarding the matter?<
>Evidence please?<
There are endless questions and discussions in Python newsgroups about the
syntax of Python tuples, you may find several of them in comp.lang.python. Some
of them:
http://groups.google.com/group/comp.lang.python/browse_thread/thread/673344303e27ed6/
http://groups.google.com/group/comp.lang.python/browse_thread/thread/699ec8cb75c7cbda/088aee81cdca92ec?lnk=gst&q=%22tuple+syntax%22#088aee81cdca92ec
Python programmers eventually always learn to manage them correctly, but many
other Python features don't generate that many discussions, this means their
syntax is not as clean and simple as many other Python features.
I've taught Python, and I've seen that I need several minutes to teach how
tuples are in Python. While such problems are not present when I explain the
Python list syntax, that is more clean.
In Python lists are arrays dynamic on the right. You need to put the items
inside square brackets. So if there's nothing between them, you have an empty
list, []. This is simple.
A Python tuple is generally not defined by the ( ) . It is defined by the comma.
So this is a tuple of 3 items:
a = (1, 2, 3)
But () is not necessary, so this too is the same tuple:
a = 1, 2, 3
So (1) is not a 1-tuple, you need a comma:
(1,)
I've seen cases where programmers forget or don't see that comma.
And there's another special case, the empty tuple. This is the only case where
the ( ) are actually part of the tuple syntax, and necessary:
()
There's another way to define an empty tuple, using the type:
tuple()
There are also some corner cases, like this one present in Python2.6 still:
>>> (a,) = (1,)
>>> () = ()
File "", line 1
SyntaxError: can't assign to ()
In the end all this doesn't cause frequent bugs in Python programs, but it's
not clean nor elegant, especially if you see this in the context of a language
as clean as Python.
> Yup, the banana notation.
It's clean, short, unambiguous, and I think it has no corner cases, so it's not
terrible. This is why Fortress uses similar syntax. It may be just sugar for
the Tuple/Record of typecons.
>> auto (car, cdr...) = expr;
> Nice.
Not invented by me :-)
>>Regarding field names for tuples, I have used Python and I like the optional
>>names of D tuples (records). In some situations you don't need names, but in
>>other situations field names are handy and help avoid bugs. In Python code
>>that processes and uses tuples contains too many [0] [1] [2] etc that aren't
>>readable and are bug-prone.<<
>Evidence please?<
I am not sure what kind of evidence you may want. The need to give a name to
tuple fields was so strong that Hettinger has added them as
collections.namedtuple, this was a early Python implementation (later
translated to C):
http://code.activestate.com/recipes/500261-named-tuples/
If you h
