How do I implement statically resolved type parameters?

Question

Specifically, I want to make a function work for all numeric types.

I've tried the following:

let isAbsoluteProductGreaterThanSum a b =
     Math.Abs(a * b) > (a + b)

let inline isAbsoluteProductGreaterThanSum a b =
     Math.Abs(a * b) > (a + b)

let inline isAbsoluteProductGreaterThanSum ^a ^b =
     Math.Abs(^a * ^b) > (^a + ^b)

let inline isAbsoluteProductGreaterThanSum (val1:^a) (val2:^b) =
     Math.Abs(val1 * val2) > (val1 + val2)

I did view this documentation but was still unable to resolve my question.

Szer · Accepted Answer · 2018-04-23 14:57:08Z

10

This will work just fine:

let inline isAbsoluteProductGreaterThanSum a b =
    abs(a * b) > (a + b)

signature for this one will be like:

val isAbsoluteProductGreaterThanSum: 
    a:  ^a (requires static member ( * ) and static member ( + ) )->
    b:  ^b (requires static member ( * ) and static member ( + ) )
    -> bool

answered Apr 23, 2018 at 14:57

Szer

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Szer · Accepted Answer · 2018-04-24 06:38:47Z

1

I thought maybe you need explicitly made it with constraints, so here you go:

let inline isAbsoluteProductGreaterThanSum'< ^a, ^b, ^c
                                       when (^a or ^b): (static member (+): ^a * ^b -> ^c)
                                       and  (^a or ^b): (static member (*): ^a * ^b -> ^c)
                                       and   ^c       : (static member Abs: ^c      -> ^c)
                                       and   ^c       :  comparison>
                                       a b =
     let productOfAb = ((^a or ^b): (static member (*): ^a * ^b -> ^c) (a, b))
     let sumOfAb     = ((^a or ^b): (static member (+): ^a * ^b -> ^c) (a, b))
     abs (productOfAb) > sumOfAb

answered Apr 24, 2018 at 6:38

Szer

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