This is MetaPost, version 1.504 (kpathsea version 6.0.0)  24 NOV 2011 13:14
**bananadimmer.mp
(mpost.mp (/usr/share/texmf-texlive/metapost/base/plain.mp
Preloading the plain mem file, version 1.004)) (./bananadimmer.mp
(/usr/share/texmf-texlive/metapost/featpost/featpost3Dplus2D.mp
Preloading FeatPost macros, version 0.6.7)
>> banana
! Isolated expression.
<to be read again> 
                   (
l.62     banana(
                
? x

