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This expression should have type 'unit', but has type 'ConsoleKeyInfo'

I just wanted to pause in an F# console application, so I wrote:

Console.ReadKey()

But this gives the warning: This expression should have type 'unit', but has type 'ConsoleKeyInfo'.

What can I do to fix this?

like image 388
Lee Richardson Avatar asked Nov 28 '08 01:11

Lee Richardson


1 Answers

Solution:

Console.ReadKey() |> ignore

Explanation: Console.ReadKey() returns an object of type 'ConsoleKeyInfo' but you're using it as a statement without assigning the return value to anything. So F# warns you that you're ignoring a value. ignore takes any type and returns nothing. It could be defined like this:

let ignore _ = ()
like image 78
namin Avatar answered Oct 22 '22 03:10

namin