The documentation for getTerminalSize says

My understanding of this was that if the preconditions do not hold (either terminal does not support cursor movement or stdin is not available), getTerminalSize :: IO (Maybe (Int, Int)) will return Nothing. I was surprised to learn that this is not the case.

Namely, running main = getTerminalSize >>= print with redirected stdin fails with an IO exception:

$ ./GetTerminalSize.hs < /dev/null
GetTerminalSize.hs: Uncaught exception ghc-internal:GHC.Internal.IO.Exception.IOException:

<stdin>: hWaitForInput: end of file

HasCallStack backtrace:
  ioException, called at libraries/ghc-internal/src/GHC/Internal/IO/Handle/Internals.hs:353:11 in ghc-internal:GHC.Internal.IO.Handle.Internals

Is it intended? Not the end of the world, but I feel like getTerminalSize could have caught the exception and return Nothing instead of passing the bucket to a caller.