[英]Difference between list and [] in F#
I am porting some Haskell code to F# but a bit confused about the collections available and their signatures in F#. 我正在将一些Haskell代码移植到F#,但对F#中可用的集合及其签名有点困惑。 My understanding is that elements in lists are enclosed between [ ], sequences between { }, and arrays between [| 我的理解是列表中的元素包含在[]之间,{}之间的序列和[|之间的数组]之间 |]. |]。 In F# Interactive, I get the following when I create each container with 5 ints. 在F#Interactive中,当我用5个int创建每个容器时,我得到以下内容。
// List
> [1..5]
val it : int list = [1; 2; 3; 4; 5]
// Seq
> {1..5}
val it : seq<int> = seq [1; 2; 3; 4; ...]
// Array
> [|1..5|]
val it : int [] = [|1; 2; 3; 4; 5|]
What confuses me is that the type signature for arrays is int []
. 令我困惑的是,数组的类型签名是int []
。 May be type int array
or int [||]
would be less confusing? 可能是类型int array
或int [||]
会不那么混乱? Looking at the type signature, I tend to think it is a list, especially because an empty list is also represented as []. 查看类型签名,我倾向于认为它是一个列表,特别是因为空列表也表示为[]。
One question here: why is sequence type seq<int>
and not int seq
. 这里有一个问题:为什么序列类型为seq<int>
而不是int seq
。 I am assuming this may be syntactic sugar but may be there is something else behind this. 我假设这可能是语法糖,但可能还有其他背后的东西。
Now creating new types using the collection: 现在使用集合创建新类型:
type T1 = T1 of int list
type T2 = T2 of int seq // becomes type T2 = T2 of seq<int>
type T3 = T3 of int array
type T4 = T4 of int []
Is T3 and T4 the same thing? T3和T4是一回事吗?
F# allows you to use .Net style type definitions and ocaml style type definitions. F#允许您使用.Net样式类型定义和ocaml样式类型定义。 These are the same. 这些都是一样的。
int list
list<int>
int seq
seq<int>
int array
array<int>
Some Expressions in F# are F#中的一些表达式是
[||] is an array
[] is a list
{} is a sequence
In a type definition you can also do int []
. 在类型定义中,您也可以执行int []
。 Which is C like syntax sugar. 哪个是C语法糖。 Yep, T3 and T4 are the same. 是的,T3和T4是一样的。
You can't however do this []<int>
. 但是你不能这样做[]<int>
。 []
is a bit strange since it behaves as the type array in a type definition and as op_Nil in an expression. []
有点奇怪,因为它在类型定义中表现为类型数组,在表达式中表现为op_Nil。
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