Add a symbol for FSI to check whether it's in 64 bit or 32 bit

**Submitted by Max on 2/5/2015 12:00:00 AM**
**4 votes on UserVoice prior to migration**

Often I want to reference different libraries based on whether the FSI is running in 32 bit or 64 bit mode. I often have to test two versions of an assembly, and it's enough of a pain just changing the flag every time, let alone change the references. Being able to do:

``` fsharp
#if 64_BIT
#r "My64BitLib.dll"
#else
#r "My32BitLib.dll"
#endif
```
## Response

*\* by fslang-admin on 7/17/2015 12:00:00 AM **

This is approved for inclusion in a future release of F# subject to an implementation and detailed design. A pull request to implement this feature will be necessary and we encourage contributors to submit one with adequate design detail and testing to http://github.com/Microsoft/visualfsharp. Discussion of the particular version for this to be included in can be made once an implementation is available.

Design detail can also be discussed below.

Don Syme, F# Language and Core Library Evolution.

**[Original UserVoice Submission](https://fslang.uservoice.com/forums/245727-f-language/suggestions/7055281)**
[Archived Uservoice Comments](../tree/master/archive/suggestion-7055281-add-a-symbol-for-fsi-to-check-whether-it-s-in-64.md#comments)