What exactly is the return type of the printfn function in F#?

user_3771427 0
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I looked up the documentation of printfn here and this is what it says:

printfn format

Print to stdout using the given format, and add a newline.

format : TextWriterFormat<'T> The formatter.

Returns: 'T The formatted result.

But if I type the following in FSI

> let v = printfn "Hello";;
Hello
val v : unit = ()

it states that v (the return value of printfn) is of type unit.

This seems inconsistent, but I guess I am missing something here, so can anybody help me out ?

f#
1 Answers

It's not inconsistent. In your example, the format is of type TextWriterFormat<unit>, so the final return type is unit, because 'T is unit.

If you had written let v = printfn "Hello %s", then the type of v would be string -> unit. This is how F# provides type-safe string formatting.

user_3442230
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