[quadrangle]

Donate to Free/Libre/Open projects working on this instead of locked-down proprietary ones. There are two promising projects approaching (not all there yet) exactly what you want: https://atom.io/packages/ide-haskell for Atom and http://leksah.org/

[spiralpolitik]

Last I checked that the community version of IntelliJ was open source and available under the terms of the Apache license.

http://www.jetbrains.org/display/IJOS/FAQ