[英]How to specify the type of a vector of fixed size?
I am trying to use Data.Vector.Fixed
as the input to a function and am struggling to specify the vector's dimension in the type signature.我正在尝试使用Data.Vector.Fixed
作为函数的输入,并且正在努力在类型签名中指定向量的维度。
For example, I am trying to do something like the following:例如,我正在尝试执行以下操作:
acronym :: Vector (Peano 8) String -> String
acronym = foldl1 (++)
and thus specifying the vector's dimension (8) using peano numbers as defined in Data.Vector.Fixed.Cont
.因此指定使用数字皮亚诺如定义的矢量的维数(8) Data.Vector.Fixed.Cont
。
However, attempting to compile this gives kind-mismatch errors:但是,尝试编译它会导致种类不匹配错误:
...:12: error:
* Expected a type, but
`Vector (Peano 8) String' has kind
`Constraint'
* In the type signature:
acronym :: Vector (Peano 8) String -> String
|
61 | acronym :: Vector (Peano 8) String -> String
| ^^^^^^^^^^^^^^^^^^^^^^^
...:20: error:
* Expected kind `* -> *', but `Peano 8' has kind `PeanoNum'
* In the first argument of `Vector', namely `(Peano 8)'
In the type signature: acronym :: Vector (Peano 8) String -> String
|
61 | acronym :: Vector (Peano 8) String -> String
How can I specify a fixed vector's size in a type signature?如何在类型签名中指定固定向量的大小?
You're probably looking for something like:您可能正在寻找类似的东西:
{-# LANGUAGE DataKinds, FlexibleContexts, GADTs #-}
import qualified Data.Vector.Fixed as V
acronym :: (V.Vector v String, V.Dim v ~ 8) => v String -> String
acronym = V.foldl1 (++)
The type class constraint Vector v String
indicates that v
is a vector with elements of type String
, while the constraint Dim v ~ 8
ensures it has the right size.类型类约束Vector v String
表示v
是一个具有String
类型元素的向量,而约束Dim v ~ 8
确保它具有正确的大小。
It can be used with specific vector types, like boxed or continuation vectors, like so:它可以与特定的向量类型一起使用,例如盒装向量或连续向量,如下所示:
import qualified Data.Vector.Fixed.Boxed as BV
import qualified Data.Vector.Fixed.Cont as CV
eight = ["one","two","three","four","five","six","seven","eight"]
main = do
print $ acronym (V.fromList eight :: BV.Vec 8 String)
print $ acronym (V.fromList eight :: CV.ContVec 8 String)
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