I've been adding CallStack to Cabal's source code, and I noticed a common pattern that doesn't seem to be supported by the GHC.Stack API. Imagine I'm writing a general purpose logging function: debug :: Verbosity -> String -> IO () I'd like this function to print out the SrcLoc of the person who called; as an additional requirement, I only want to print the top-most stack frame by default (someone can ask for the full stack if they really want to). If I look at callStack, it is going to contain a stack frame for debug itself. That's not so great; the obvious way to fix this is to pop off the irrelevant frame manually. But now suppose that I have a pprDebug which itself calls debug. I don't want pprDebug to show up in the stack frame! Declaratively, I want to say, "Please don't add me to the call stack", at the function *definition*, not the call-site (which is what withFrozenCallStack) gives me. Does this seem like a reasonable request? I have several other ways to do this: - You could just use withFrozenCallStack at the definition site. Then when pprDebug calls debug, debug will get the call stack that pprDebug had; thus, there will always only be one irrelevant frame to pop off. - One problem with using withFrozenCallStack is that you *do* lose useful trace information, which you kind of might actually want if you are being verbose. So it almost seems like, the frozen API should still *push* frames, but just not make them visible by default. - Something that does NOT work is having functions edit the call stack to remove themselves. There's no way to tell if the stack is frozen or not, and thus no way to tell if you are actually on the stack (and need to remove it.) Thanks, Edward