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Type inference limitation with records and SRTP #685
Description
Description
Type inference for records is a bit special in F# and it doesn't play well with SRTPs
I've seen many cases, but here's a cool one:
#r "nuget: FSharpPlus"
open FSharpPlus
type Station = { Icao: string; Lat: float; Lon: float; Raw: string }
let private parseStations (json: string) =
["1"; "2"]
|> List.choose<_, Station> (fun e ->
let str (n: string) : string option = tryParse<int> n |> Option.map string
let num (n: string) : float option = tryParse<int> n |> Option.map float
applicative {
let! icao = str "icaoId"
and! raw = str "rawOb"
and! lat = num "lat"
and! lon = num "lon"
return { Station.Icao = icao; Station.Lat = lat; Station.Lon = lon; Station.Raw = raw }
})Note that this fails when it has more that 3 parameters in the final binding (I have 4 in the code)
Known Workarounds
Add type parameter annotation in the choose about the record type:
#r "nuget: FSharpPlus"
open FSharpPlus
type Station = { Icao: string; Lat: float; Lon: float; Raw: string }
let private parseStations (json: string) =
["1"; "2"]
|> List.choose<_, Station> (fun e ->
let str (n: string) : string option = tryParse<int> n |> Option.map string
let num (n: string) : float option = tryParse<int> n |> Option.map float
applicative {
let! icao = str "icaoId"
and! raw = str "rawOb"
and! lat = num "lat"
and! lon = num "lon"
return { Station.Icao = icao; Station.Lat = lat; Station.Lon = lon; Station.Raw = raw }
})Expected behavior
Workaround not needed.
This is an F# type inference limitation and should be solved in the F# compiler.
Actual behavior
No response
Configuration
No response
Reproduction Steps
No response
Are you willing to help with a pull-request?
No
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