[O] Symbol’s value as variable is void: haskell-prompt-regexp

[Roger Mason]

Hello,

GNU Emacs 25.3.1 (i386-portbld-freebsd11.1, GTK+ Version
3.22.29) of 2018-04-26

Org mode version 9.1.13 (release_9.1.13-784-ged7d1d @ 
/home/rmason/.emacs.d/org-git/lisp/)

Attempting to run a haskell code block:

#+begin_src haskell :exports results 
cations=["Na","Mg","Al","Si","K","Ti","Fe"]
atwt=[22.9897,24.305,26.9815,28.0855,39.0983,47.867,55.845]
nanmol=[1,1,3,2,1,2,3]
ncatmol=[2,1,2,1,2,1,2]
anwt= replicate (length atwt) 15.9994
#+end_src

gives this message:
executing Haskell code block...
run-hooks: Symbol’s value as variable is void: haskell-prompt-regexp

Any help in solving this will be most appreciated.

Thanks,
Roger