Dear R-Devel, we use R on 32 and 64 bit versions of RHEL AS 4 (U5) where the default compiler is gcc 3. However recently we have had problems updating MCMCpack which appears to require gcc4. I have a few questions. a) Is it OK to mix and match gcc3 and gcc4? b) Should we recompile the whole of R under gcc4? c) On posting to the RHEL 4 list one respondent said not to touch gcc4 with a barge pole. Is this valid? d) What is the safest way to change compiler options for compiling particular R modules. I have been really impressed with CRAN and the automatic compiling/updating of modules - the only glitch being the occasional failure of compilations that require Tcl/Tk - interactive updating solves this though it is a little annoying. However are more modules going to require gcc4? thanks iain ps I'm a sysadmin rather than a programmer so apologies in advance :-> ---------------------------------------- Iain Morrison IT Manager MRC Epidemiology Unit Institute of Metabolic Science Box 285 Addenbrooke's Hospital Hills Road Cambridge CB2 0QQ Tel 01223 769200