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Having problems using a discriminated union of records
f#

Can a list of discriminated unions where each discriminator is a record work?

The example below creates a discriminated union of records and filters the list:

type Arecord = {a:string; b:string}
type Brecord = {a:string}

type RecordType =
| Atype of Arecord
| Btype of Brecord

let alist =
[
Atype {a = "x" ; b ="y"} ; Btype {a = "z"}
]

let filterList l =
l
|> List.filter(fun i -> i.a = "x")

However, when you specify

filterList aList F# Interactive throws the following exception:

error FS0001: Type mismatch. Expecting a

Brecord list

but given a

RecordType list

The type 'Brecord' does not match the type 'RecordType

How can I specify the right type to pass in a RecordType and ensuring that the list returned is a filtered list of RecordType?

Also is usin

.

Try either

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let filterList l  =
    l
    |> List.filter(function | Atype i ->  i.a = "x" | _ -> false)

or

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let filterList l  =


    l


    |> List.filter(function | Atype {a="x"} ->  true | _ -> 

false)
By on 10/21/2010 3:47 PM ()

Thank you for this.

By on 10/22/2010 12:11 AM ()

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