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DynamicInvocationNotSupportedException: op_Subtraction
f#

I played a little with quotations:

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#light
open Microsoft.FSharp.Quotations.Patterns

let rec eval = function
    | Call (None,m,a) ->
        let args = List.map eval a |> Array.of_list
        m.Invoke(null, args)
    | Value (o,t) -> o
    | o -> failwith (sprintf "Unsupported expression %A" o)

let plus x y = <@ x + y @>
let minus x y = <@ x - y @>

plus 3 2 |> eval |> printfn "%O"
minus 3 2 |> eval |> printfn "%O"

The first call to eval yields 5 as expected. The second yields:System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> Microsoft.FSharp.Core.DynamicInvocationNotSupportedException: op_Subtraction
Any thoughts on what's going on here?

.

Looking at the Operators class in the Microsoft.FSharp.Core namespace in Reflector, it appears that for some reason many of the operators throw that exception when called (not just subtraction but also op_Multiplication, op_Division, op_BitwiseAnd, etc.). However, there are many operators besides addition that will work, including things like op_Exponentiation, so I'm not sure what the reason for this behavior is...

By on 2/4/2009 8:50 AM ()

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