How to make my function generic
let csvList startDelim endDelim lst memF =
let listIter (listStr: string) item =
if listStr.Length > 0 then
listStr + "," + (memF item)
else
memF item
startDelim + (List.fold listIter "" lst) + endDelim
let listIntoJsonArray = csvList "[" "]"
let listIntoJsonObject = csvList "{" "}"
let intConverter (item:int) : string =
item.ToString()
let objectConverter (item:SomeObject) : string =
item.value.ToString()
let objects = [{vaue: 12.3}; {vaule: 33.2}]
let ints = [1;2;4]
let o = listIntoJsonObject objects objectConverter
let i = listIntoJsonObject ints intConverter
I can't seem to find the magic sauce to make the csvList or its par开发者_如何学编程tially applied helpers listIntoJsonArray or listIntoJsonObject generic.
Thanks for the help.
Your listIntoJsonArray and listIntoJsonObject are values, not functions, so you met value restriction monster. You can either convert them to functions by adding explicit argument or to type functions.
// function case
let csvList startDelim endDelim lst memF =
let listIter (listStr: string) item =
if listStr.Length > 0 then
listStr + "," + (memF item)
else
memF item
startDelim + (List.fold listIter "" lst) + endDelim
let listIntoJsonObject x = csvList "{" "}" x
let ints = [1;2;4]
let i = listIntoJsonObject [1;2;4] string
let y = listIntoJsonObject ["123"] id
// type function case
let csvList<'T> startDelim endDelim (lst : 'T list) memF =
let listIter (listStr: string) item =
if listStr.Length > 0 then
listStr + "," + (memF item)
else
memF item
startDelim + (List.fold listIter "" lst) + endDelim
[<GeneralizableValue>]
let listIntoJsonObject<'T> = csvList<'T> "{" "}"
let ints = [1;2;4]
let i = listIntoJsonObject [1;2;4] string
let y = listIntoJsonObject ["123"] id
I haven't tried the code, but in general, eta-conversion, e.g. changing
let myFunVal = partialApplication toSomeArgs
to
let myFun rest = partialApplication toSomeArgs rest
is likely to fix this.
csvList
looks generic enough: string -> string -> 'a list -> ('a -> string) -> string
But you've encountered Value Restriction in your attempt at partial application with listIntoJsonArray
and listIntoJsonObject
; you need to add explicit parameters:
let listIntoJsonArray lst memF = csvList "[" "]" lst memF
let listIntoJsonObject lst memF = csvList "{" "}" lst memF
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