I'm rewriting some old code,originally written for ghc-4.08.2 . 1)Now, when I compile with ghc-5.02 , fails: ghc -cpp -fglasgow-exts -O -fvia-C -syslib lang -syslib concurrent -c foo.hs foo.hs:47: failed to load interface for `PrelAddr': Could not find interface file for `PrelAddr' gmake: *** [foo.o] Error 1 2)if commented, --import PerlAddr ghc -cpp -fglasgow-exts -O -fvia-C -syslib lang -syslib concurrent -c foo.hs foo.hs:112: Type constructor or class not in scope: `Addr' foo.hs:514: Data constructor not in scope: `A#' gmake: *** [foo.o] Error 1 3)In doc available I'm recommended to import Foreign import Foreign ghc -cpp -fglasgow-exts -O -fvia-C -syslib lang -syslib concurrent -c foo.hs foo.hs:511: Data constructor not in scope: `A#' gmake: *** [foo.o] Error 1 What should I import to use unboxed types and constructors ? You see the "-fglasgow-exts" .