The static optimization conditionals allow one to create functions that can generate different code depending on the input parameter's type at compile time thus improving performance.

I'd like to create the following function:

let inline guid (s:^a) =

failwith "TypeNotSupported"

when ^a : string = System.Guid(s)

when ^a : byte[] = System.Guid(s)

when ^a : (int*int16*int16*byte[]) = let a,b,c,d = x in System.Guid(a,b,c,d)

when ^a : (uint32*uint16*uint16*byte*byte*byte*byte*byte*byte*byte*byte) = let a,b,c,d,e,f,g,h,i,j,k = s in System.Guid(a,b,c,d,e,f,g,h,i,j,k)

when ^a : (int*int16*int16*byte*byte*byte*byte*byte*byte*byte*byte) = let a,b,c,d,e,f,g,h,i,j,k = s in System.Guid(a,b,c,d,e,f,g,h,i,j,k)

when ^a : unit = System.Guid.Empty

Instead I'm told that the when clauses are ONLY allowed in the F# library. This is a great language feature along with the (# ... #) inline CIL feature that have been deprecated.

Why not allow both these features for general code.