在fp-ts和函数式编程中管理monad数组 [英] Managing array of monads in fp-ts and Functional Programming
问题描述
我对函数式编程非常陌生,我在数组上遍历很费劲。
当我阅读这本书看来我应该能够简单地在Monad之间来回走动,但是我无法用 fp-ts 。
有人可以使用 array.traverse / sequence
或其他任何方式解释以下内容吗?
- 如何从
TaskEither< Error,string []>
转到TaskEither< Error,Either< Error,string> []>
;还是有一种更好的方法可以使单个错误变为嵌套错误,同时又使输入保持简单? - 如何从
TaskEither< Error,Either< Error ,string []>>
到类似TaskEither< Error,Option< string []>>
之类的东西;还是应该映射该函数的结果以返回到c?
考虑以下简化代码,以更好地了解我们对这些数组的处理方式:
//辅助函数
声明函数toItems(input:string):TaskEither< Error,string []);
声明函数toTitle(item:string):要么<错误,字符串> ;;
声明函数clean(item:string):Option< string> ;;
//这是我到目前为止尝试过的
const program =(input:string)=> pipe(
toItems(input),//我们有TaskEither< Error,string []>
TE.map(items => array.traverse(two)(items,toTitle)),/ /现在我们有了TaskEither< Error,Either< Error,string []>>
TE.map(items => array.traverse(option)(items,clean)),//清理都不起作用()从这里
)
严格地说,适用足以满足遍历
-您不需要单子。
TaskEither<错误,字符串[ ]>
到TaskEither< Error,Either< Error,string> []>
?
const program1 =(输入:字符串)=>
P.pipe(
toItems(input),
TE.map(A.map(toTitle))
);
TaskEither< Error,Either< Error,string []> ;>
到TaskEither< Error,Option< string []>
?
const program2 =(输入:字符串)=>
P.pipe(
toItems(input),
TE.map(item => A.array.traverse(O.option)(items,clean))
) ;
具体选择的结构取决于您的环境和目的。 ▶选项
:强调缺席/在场; ▶任一个
:允许在左
中使用更具体的错误类型。
让我们看一些程序,然后想象一下,所有程序都使用带有 TaskEither
的Web API。
程序3:
(输入:字符串)=> TE.TaskEither< Error,string []>
▶将完全失败,并出现 Error
或以 string []
提取的数据成功
程序4:
(input:string)=> TE.TaskEither< Error,E.Either< Error,string []>>
▶ fetch
会导致错误
或成功。如果成功,则进一步处理Web数据-导致错误
或 字符串[]
程序5:
(输入:字符串)=> TE.TaskEither<错误,E.Either<错误,字符串> []>
▶与计划4相同,但对Web数据的后处理导致多个 任何一个
结果-每个可以失败或成功
这是程序4的某种中间立场:
const program4 =(
输入:字符串
):TE.TaskEither<错误,E.Either<错误,string []> =>
P.pipe(
toItems(input),// TE.TaskEither<错误,string []>
TE.map(items => // TE.TaskEither< E, E.Ether<错误,string []>
A.array.traverse(E。任一)(// E.Either<错误,string []>
项目,
F.flow(// E.Ether< Error,string>
toTitle,
E.chain(s => E.fromOption(()=> Error())(clean(s )))
)
)
)
);
I'm very new to Functional Programming and I'm struggling a lot with running traverse on arrays.
When I read this book it seems that I should be able to simply traverse between Monads but I can't wrap my head around this concept with fp-ts.
Can someone explain the following using array.traverse/sequence
or any other ways please?
- How can I go from
TaskEither<Error, string[]>
toTaskEither<Error, Either<Error, string>[]>
; or is there a better way to go from a single error to nested errors while keeping the typings simple? - How can I go from
TaskEither<Error, Either<Error, string[]>>
to something likeTaskEither<Error, Option<string[]>>
or something similar; or should we map the result of that function to turn back toEither
?
Consider the following simplified code to have a better idea what we are doing with these arrays:
// helper functions
declare function toItems(input: string): TaskEither<Error, string[]);
declare function toTitle(item: string): Either<Error, string>;
declare function clean(item: string): Option<string>;
// This is what I tried so far
const program = (input: string) => pipe(
toItems(input), // we have TaskEither<Error, string[]>
TE.map(items => array.traverse(either)(items, toTitle)), // now we have TaskEither<Error, Either<Error, string[]>>
TE.map(items => array.traverse(option)(items, clean)), // nothing works with clean() from here
)
Strictly spoken, Applicative is sufficient for traverse
- you don't need a monad.
TaskEither<Error, string[]>
toTaskEither<Error, Either<Error, string>[]>
?
const program1 = (input: string) =>
P.pipe(
toItems(input),
TE.map(A.map(toTitle))
);
TaskEither<Error, Either<Error, string[]>>
toTaskEither<Error, Option<string[]>>
?
const program2 = (input: string) =>
P.pipe(
toItems(input),
TE.map(items => A.array.traverse(O.option)(items, clean))
);
The concrete chosen structure depends your environment and purpose. ▶ Option
: emphasis on absence/presence ; ▶ Either
: permits a more concrete error type in Left
.
Let's look at some programs and imagine, all use a web API with TaskEither
.
(input: string) => TE.TaskEither<Error, string[]>
▶ will either fail completely with Error
or succeed with string[]
fetched data
(input: string) => TE.TaskEither<Error, E.Either<Error, string[]>>
▶ fetch
results in Error
or succeeds. If succeeded, process web data further - resulting in Error
or string[]
(input: string) => TE.TaskEither<Error, E.Either<Error, string>[]>
▶ same as Program 4, but post-processing of web data results in multiple Either
results - each can fail or succeed individually
Here is implementation of program 4 as some kind of middle ground:
const program4 = (
input: string
): TE.TaskEither<Error, E.Either<Error, string[]>> =>
P.pipe(
toItems(input), // TE.TaskEither<Error, string[]>
TE.map(items => // TE.TaskEither<E, E.Either<Error, string[]>>
A.array.traverse(E.either)( // E.Either<Error, string[]>
items,
F.flow( // E.Either<Error, string>
toTitle,
E.chain(s => E.fromOption(() => Error())(clean(s)))
)
)
)
);
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