Improve error reporting: Member implementation with tuple argument(s)

[JanWosnitza]

Related to #1200

What

There is a difference between int32 * int32 -> unit and (int32 * int32) -> unit. The first one generates 2 parameters and the second one generates 1 tuple parameter. One might stumble upon this error:

type IInterface =
    abstract Function : (int32 * int32) -> unit

{ new IInterface with
    member this.Function (i, j) = ()
}

FS0768: The member 'Function' does not accept the correct number of arguments, 1 arguments are expected

Why

The error message is confusing, because one might not expect the brackets to change the overall function signature and assume to the result as with:

type IInterface =
    abstract Function : int32 * int32 -> unit

{ new IInterface with
    member this.Function (i, j) = ()
}

How

Trying to address @forki proposals ( #1200 (comment) ):

• it should be singular
• it could hint the signature of Function
• it could tell something about tuples vs. "C# style parameters"

E.g.:

FS0768: The member 'Function : (int32 * int32) -> unit' does not accept the correct number of arguments. Expecting 1 argument
    (int32 * int32)
but given are 2 arguments
    int32 * int32
Member functions with a single tuple argument are compiled to C#-ish parameters instead of a single parameter of type tuple, unless forced otherwise.

I am unsure about the "tuples vs C# style parameters" explanation (also a native speaker should choose the exact wording :) )

[JanWosnitza]

erm.. oups

[forki]

would that help:

?

I assume we would need to remove the word "abstract" from the message. and then it would already be better.

[forki]

But we still somehow need to explain the tuple issue.

[forki]

WIP PR in #1229

[forki]

like this?