How can I decode a quotedprintable encoded String?

问题

I'm writing a webmail app and need to decode Quotedprintable values in the emails header fields.

I've tried several decode functions from various packages on haskell, so far without luck.

How can I decode for example this string:

"freelancermap Newsletter:  Erfolgreich =?ISO-8859-1?Q?selbstst=E4ndig?= mit Sicherheit"

来源：https://stackoverflow.com/questions/15098452/how-can-i-decode-a-quotedprintable-encoded-string