Consider the following code
let a = 5. / 0.
let b = sin a
let c = sqrt(-5.)
It produces both Infinity and NaN. In both cases I want to have an exception thrown (for debuging purposes).
I use Visual Studio 2010. I set up Debug/Exceptions.../Common Language Runtime Exceptions/System/System.ArithmeticException to "Thrown", but when running the code, no exception is thrown.
Any idea why and how to throw an exception on NaN or Infinity?
As others noted, you'll have to check for the NaN condition explicitly. If you wanted to do this using some advanced F# features, then you could also use computation expressions.
It is possible to define a builder that automatically checks for Nan when you bind value using let!. Then you could write something like:
check { let! a = 5. / 0. // 'a' is checked here
let! b = sin a // 'b' is checked here
let c = sqrt(-5.) // 'c' is not checked (no 'let!')
return a, b, c }
This may be too complicated mechanism for just simple checks, but I find it quite nice. The definition of the computation builder looks like this (you'll need to add While, For and some others to support all language constructs):
open System
type CheckedBuilder() =
member x.Bind(v:float, f) =
if Double.IsNaN(v) |> not then f v
else raise (new ArithmeticException())
member x.Return(v) = v
let check = CheckedBuilder()