I was reading up on the documentation for alloca and friends[1], which says, "If any of the allocation functions fails, a value of nullPtrhttp://www.haskell.org/ghc/docs/7.0.2/html/libraries/base-4.3.1.0/Foreign-Pt... is produced." It seems like every example of FFI code that I find which uses alloca ignores the possibility of a nullPtr[2, 3, 4]. So then I started trying out examples with the help of dmwit and others from #haskell. It seems that actually, alloca and friends throw exceptions: dmwit> main = allocaArray (2^30) (\ptr -> print ((nullPtr :: Ptr Double) == ptr)) <dmwit> lispy: alloca also throws an exception. <dmwit> lispy: Or rather, allocaBytes throws an exception, and alloca is implemented in terms of allocaBytes, so I'm *guessing* that alloca throws an exception. I'm on a 64bit version of windows here with more than 4GB of memory to spare for the GHC process. Unfortunately, allocaBytes takes an Int so I can't test it with a request larger than the amount of physical ram I have. Just playing around with different arguments to allocaBytes I can get different behavior: <= 2^30 bytes, works perfectly == 2^30 + 2^20 bytes, I get an "<interactive>: out of memory" message and ghci terminates == 2^31-1, I get a crash where windows pops up a little dialog saying my program (ghci) has crashed. The behavior seems to be inconsistent with the documentation. What is the correct behavior for alloca and friends and should I be checking for nullPtr? Thanks, Jason [1] http://www.haskell.org/ghc/docs/7.0.2/html/libraries/base-4.3.1.0/Foreign-Ma... [2] http://en.wikibooks.org/wiki/Haskell/FFI [3] http://www.haskell.org/haskellwiki/HSFFIG/Examples [4] http://book.realworldhaskell.org/read/interfacing-with-c-the-ffi.html