January 2018 - ghc-devs

pattern signatures
by Richard Eisenberg 10 Jan '18

10 Jan '18

Hi devs, Is a pattern signature a) something you put after `pattern P ::` ? b) something you put after `::` in a pattern, as in `foo (Proxy :: Proxy a)` ? I've seen the term "pattern signature" apply to both, and I've been tripped up by this. Does anyone have terminology that unambiguously separates these two constructs that we can all adopt? Thanks! Richard

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Backing up and downloading Trac contents?
by Niklas Hambüchen 07 Jan '18

07 Jan '18

Working on something today, it came to my mind how much useful information is stored in Trac and how much time would get lost if it went down, corrupted or missing. With the source code there's no such issue as with git being a DVCS, everybody has the full history. But not so with Trac. Are there backups of Trac? Are there some publicly available ones that one could download and thus conveniently use offline? Thanks!

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Spectre mitigation
by Demi Obenour 06 Jan '18

06 Jan '18

The recent “Spectre” bug requires that speculative execution of indirect branches be disabled. For GHC, this will require passing a flag to LLVM and fixing the NCG to emit suitable calling sequences. This will be a disaster for the STG execution model, because it disables CPU branch prediction for indirect calls and jumps. This is a big argument in favor of doing a CPS→SSA conversion in the backend.

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Can't push to staging area?
by Bartosz Nitka 05 Jan '18

05 Jan '18

I'm trying to update a diff and I run into this: $ arc diff Linting... LINT OKAY No lint problems. Running unit tests... No unit test engine is configured for this project. PUSH STAGING Pushing changes to staging area... sudo: a password is required fatal: Could not read from remote repository. Please make sure you have the correct access rights and the repository exists. STAGING FAILED Unable to push changes to the staging area. Usage Exception: Failed to push changes to staging area. Correct the issue, or use --skip-staging to skip this step. I believe that it worked for me before with my setup, and I seem to be in compliance with https://ghc.haskell.org/trac/ghc/wiki/Phabricator#Startingoff:Fixingabugsub… Any ideas? Thanks, Bartosz

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