OK. Let's make sure the wiki page and documentation reflects this. Thanks SImon | -----Original Message----- | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Eric | Seidel | Sent: 27 January 2016 18:16 | To: ghc-devs@haskell.org | Subject: Re: CallStack naming | | On Thu, Jan 21, 2016, at 04:07, Simon Peyton Jones wrote: | > | It’d probably need a built-in function | > | | > | setCallStack :: CallStack -> (AppendsCallStack => a) -> a | > | > Correct. This is easy to write in Core but not in Haskell. | | Ugh, I just realized that we can't write setCallStack (with implicit | parameters) in Haskell either. Well, we can, but it adds an entry to | the stack.. Why? Let's look at the implementation | | setCallStack :: CallStack -> (HasCallStack => a) -> a | setCallStack stk do_this = | let ?callStack = stk in do_this | | Rebinding ?callStack works just fine, but the occurrence of do_this | causes GHC to push an entry onto the stack, which is less than ideal. | | What does this look like in practice? If we evaluate | | setCallStack foo (error "die") | | the resulting stack will be | | error | *do_this* | foo | | The rebinding trick works for withFrozenCallStack precisely because we | freeze the CallStack, so the push from do_this is ignored. | | So, long story short, I'm not convinced of the utility of setCallStack. | I think perhaps we should not provide it, and just do the rebinding | trick inside withFrozenCallStack (which was the only use-case for | setCallStack to begin with). | _______________________________________________ | ghc-devs mailing list | ghc-devs@haskell.org | https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fmail.ha | skell.org%2fcgi-bin%2fmailman%2flistinfo%2fghc- | devs%0a&data=01%7c01%7csimonpj%40064d.mgd.microsoft.com%7c37a3c50163ce4 | 0dc0ee408d32745f348%7c72f988bf86f141af91ab2d7cd011db47%7c1&sdata=dVg%2b | q2D%2b2mgmgSWh8Ic9o09P%2f9mem4CpDgd0YzZZpPc%3d