var x = 1;
compiles and runs just fine while
let x = 1
in F# expression or program does not.
I believe this is due to LINQPad being stuck on an older version of F# - because of this issue:https://github.com/dotnet/fsharp/issues/8560
The good news is this issue is part of the 16.10 milestone, so I'm optimistic that we'll see a fix soon.