31 Jan
2003
31 Jan
'03
8:08 a.m.
Pavel G. Zhbanov wrote:
Is it even possible to make a "global variable" in Haskell? If yes, how?
The usual fudge is:
import IORef import IOExts
globalVar :: IORef Int globalVar = unsafePerformIO $ newIORef 0
However, beware of creating more than one "global variable" of the same type. If you enable optimisation, common subexpression elimination may result in both names referring to the same IORef.
John Hughes wrote a nice pearl on the subject, see http://www.math.chalmers.se/~rjmh/Globals.ps Cheers, Ralf