[Haskell] Issue about use of WinHugs

Hi, list I'm new to WinHugs, what's wrong with isUpper of my WinHugs? Hugs> filter isUpper "ABCDEfgh" ERROR - Undefined variable "isUpper" Hugs> filter Char.isUpper "ABCDEfgh" ERROR - Undefined qualified variable "Char.isUpper" Hugs> :version -- Hugs Version Sep 2006 Best Regards, bingfeng