Hi Simon,
This is clearly a misuse of unsafePerformIO (as I'm sure you're aware). Just out of interest - what's the context?
I am writing an optimiser for Yhc, doing whole-program optimisation, with the intention of keeping it fast and high performance. Since writing out Yhc bytecode would kill any performance benefits, I am writing back to Haskell to be compiled with GHC. So the basic sequence of steps is: compile Haskell to Yhc Core transform Yhc Core convert Yhc Core to Haskell compile Haskell to GHC The problem I'm currently overcoming is that Yhc inserts its own IO monad, which isn't the same as the GHC one. By the time I get to GHC Haskell, all of the Yhc monad is invisible to GHC, so I have to unsafePerformIO the getchar/putchar functions. With this as the primitive getchar, it seems to work for my particular example, but is clearly a bit fragile. All the examples I'm doing for now are wc -c, wc -l, so shouldn't stress the IO much more than getchar/putchar. Thanks Neil