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Type Inference, signature file and operator overloading
f#

This raises an error arguing that both types are different.

If I don't use the inline keyword : I have the "int" type inference issue.

Is there any way to make this work ?

(Basically, it's a <range> module where type 'a t = {upper_bound : 'a ; lower_bound : 'a}

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//file.fsi
val length : 'a t -> 'c when 'a : (static member (-) : 'a * 'a -> 'c)

//file.fs
let inline length (r : 'a t) = r.upper_bound - r.lower_bound

The same issue appears (although just on the type inference side) in examples such as the following where an error is raised because value is inferred to be an integer (due to the let ... = (value - foo))

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let transform (range1 : 'a Range) (range2 : 'a Range) (value : 'a) = 
  let relative_distance_from_min = (value - range1.lower_bound) / (Range.length range1)
  range2.lower_bound + (relative_distance_from_min * (Range.length range2))

Thanks a lot for any help/insight you can provide me with !!!

j

.

Hi,

actually, the type of range can be numeric, but it doesn't have to be (although the logic remains), for instance it could be a date range... or any "sortable" and "measurable" type.

For what it's worth, the error messages were cleared by changing the length signature to
val inline length : ^a t -> ^b when ^a : (static member ( - ) : ^a * ^a -> ^b)

And adding the "inline" keyword to the functions calling (-). Of course, it's not perfect, but it works for the purpose...

In any case, thanks a lot for the help, especially on a week-end!!!!! :-)

Julien

By on 7/28/2007 8:33 AM ()

I believe you want "transform" to be generic over a numeric type. To do this you should either pass in the subtraction function for the type as an explicit argument or else pass an instance of INumeric<'a> in as an argument. Alternatively you can store an instance of INumeric<'a> in your Range data structure.

Kind regards

don

By on 7/28/2007 4:28 AM ()

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