When List.transpose is given a list containing an empty sublist, all sublists after the empty sublist are discarded.
It's easier to explain by example:

> List.transpose [[true; true]; []; [false; false]];;
val it : bool list list = [[true]; [true]]

compared to:

> Array.transpose [| [|true; true|]; [||]; [|false; false|] |];;
System.ArgumentException: The arrays have different lengths.
array.[0].Length = 2, array.[1].Length = 0
Parameter name: array.[0]
   at Microsoft.FSharp.Core.DetailedExceptions.invalidArgDifferentArrayLength[?](String arg1, Int32 len1, String arg2, Int32 len2)
   at Microsoft.FSharp.Collections.ArrayModule.transposeArrays[T](T[][] array)
   at Microsoft.FSharp.Collections.ArrayModule.Transpose[T](IEnumerable`1 arrays)
   at <StartupCode$FSI_0018>.$FSI_0018.main@()
Stopped due to error

And:

> Seq.transpose [[true; true]; []; [false; false]];;
val it : seq<seq<bool>> = seq [seq [true; false]; seq [true; false]]

though the Seq.transpose behavior is understandably quite different.

Provide the steps required to reproduce the problem:

1. open FSI
2. enter List.transpose [[true; true]; []; [false; false]];;

Expected behavior

I would expect it to throw an exception just like the Array.transpose implementation, or maybe just filter out empty sublists, such that List.transpose [[true; true]; []; [false; false]] would return [[true; false]; [true; false]]

Actual behavior

List.transpose discards any sublists after the first empty sublist (from what I can tell). For the particular case of List.transpose [[true; true]; []; [false; false]] it returns [[true]; [true]]

Known workarounds

1. check that all the sublists have the same length before calling transpose, and handling the error case directly.
2. convert to a seq of arrays and use Array.transpose

Related information

• Windows 10
• FSI shipped with Visual Studio 2019 16.1.0, particularly
  C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\Common7\IDE\CommonExtensions\Microsoft\FSharp\fsi.exe