Question

So I’ve written a little binary search function (not that I need to, but just because I can), and when I make it specific to strings or to integers, for example, it works well. When I attempt to use a generic type signature, I start getting exceptions.

A copy of the function using a generic type, 'a:

let search (needle : 'a) (haystack: 'a array) : int = 
    let length = Array.length haystack

    if Array.length haystack <= 0
    then -1
    else
        let bottom = 0
        let top = Array.length haystack - 1

        let rec search' (needle : 'a) (haystack: 'a array) (bottom:int) (top:int) : int = 
            if bottom = top
            then if needle = haystack.[top] then top else -1
            else
                let middle = (uint32 top + uint32 bottom) >>> 1 |> int  // avoid an overflow

                if needle <= haystack.[middle]
                then search' needle haystack bottom middle
                else search' needle haystack (middle+1) top

        search' needle haystack bottom top 

When this is called, I get the following:

System.InvalidProgramException: Invalid IL code in FSI_0019:search'@921-13<a> (a,a[],int,int): IL_0000: br        IL_0005
  at FSI_0019.search[String] (System.String needle, System.String[] haystack) [0x00000] in <filename unknown>:0 
  at <StartupCode$FSI_0023>.$FSI_0023.main@ () [0x00000] in <filename unknown>:0 
  at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (object,object[],System.Exception&)
  at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0 
Stopped due to error

Am I doing something wrong? (Again, when I use string or int instead of 'a, everything works…)

Edit:

I’ve compiled Mono 2.9 or so, and this function then works in FSI. Now, to wait for Debian and Ubuntu to upgrade… 😀

Answer 1

Mono bug.
Before, I had a code that does not work on fsi but works compiled.

EDIT: It’s confirmed that that code doesnt work on fsi, but works with compiled by fsc.