A tuple can have any number of elements. (1,2) is a 2-tuple. (1,2,3) is a 3-tuple. (x:xs) and (x,y) are differently typed: xs must be a list of the type of x, while y can be any type. (x:xs) is not a tuple. It is a list by definition. On Wed, Feb 24, 2016 at 2:45 AM Imants Cekusins wrote:

Hello Xiao,

(one_element) -- is evaluation (element,element,...) -- is tuple

(1:[2]) -- [1,2] because it is one "array element" (1,2) -- is a tuple because there are 2 elements _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners

Hi all, Firstly, thanks very much for all responses! Rein referred "A tuple can have any number of elements", while Graham referred "There's no "one-ple", or 1-tuple, in Haskell.". So which one is right? The tuple at least contains 2 elements? Thanks very much in advance! Best Regards Nan Xiao On Thu, Feb 25, 2016 at 2:37 AM, Graham Gill wrote:

Hi Nan, are you just confused about the use of the parentheses "(" and ")"?

(x1,x2), (x1,x2,x3), ... are tuples in Haskell, but (x:xs) is not. (There's no "one-ple", or 1-tuple, in Haskell.) In

occurs value [] = 0 occurs value (x:xs) = (if value == x then 1 else 0) + occurs value xs

the "(" and ")" around "x:xs" are just there for grouping, for operator precedence reasons. Function application binds more tightly than ":". If you leave the parentheses off, such as in

occurs value x:xs = ...

you'll get a parse error.

Graham

On 2/24/2016 5:31 AM, Nan Xiao wrote:

...

Hi all,

Greetings from me!

I am confused about the function parameters and tuple. E.g.:

occurs value [] = 0 occurs value (x:xs) = (if value == x then 1 else 0) + occurs value xs

should we consider (x:xs) as a tuple?

Thanks in advance!

Best Regards Nan Xiao _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners

_______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners

The way I learned it: A tuple type is defined by the types inside it, so an (int,int) is not the same type as an (int, maybe(int)). With a one-tuple the type would just be (int) and that provides zero benefit. Instead of trying to do `first (...my expression...)` to get the first element of the one tuple, it just becomes the value inside. Sent from my iPhone

On Feb 24, 2016, at 7:02 PM, Imants Cekusins wrote:

My guess is: tuple must contain 2+ elements.

Try to enter (1) in ghci. It is displayed as 1

Parentheses are only recognized as a tuple if there are elements separated by a comma. Otherwise an expression is assumed.

_______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners

Nan, generally speaking (e.g., in maths) tuples can contain any number of elements. Haskell specifically disallows one-tuples because of the ambiguity in parsing them. Instead, (expr) is just evaluated as expr. On the other hand, it does allow (), which is a zero-tuple. Haskell's compilers also impose an upper bound on the practical size of a tuple (for modern GHC, that's 61, as Max mentioned) but that isn't a restriction of the Haskell language itself. If you want, you can consider Identity a to be a one-tuple, but it obviously doesn't use tuple syntax. As a side note, a 1-tuple is occasionally called a monad in other disciplines, while a monad is actually defined as a triple (a three-tuple) in maths. None of that is relevant to Haskell though. On Thu, Feb 25, 2016 at 7:14 AM Max Voit wrote:

On Thu, 25 Feb 2016 07:49:56 +0800 Nan Xiao wrote:

...

Rein referred "A tuple can have any number of elements", while Graham referred "There's no "one-ple", or 1-tuple, in Haskell.". So which one is right? The tuple at least contains 2 elements?

There is no one-tuple; however, there's a zero-tuple. Also no arbitrary number of tuple elements allowed, due to definition (we're at 61 for some reason). Refer to

http://hackage.haskell.org/package/ghc-prim-0.4.0.0/docs/GHC-Tuple.html

best, Max _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners