Encoding does not seem to be portable between GHC and GHCJS

[tysonzero]

The following code:

print . fmap ord . unpack $ flat (Right (20, 30) :: Either Int (Double, Double))

Gives [160,26,0,0,0,0,0,0,32,31,0,0,0,0,0,0,1] in GHC.

But [32,26,0,0,128,0,0,0,32,31,0,0,0,0,0,0,1] in GHCJS.

Specifically ghc 8.0.2 and ghcjs 0.2.1 (ghc 8.0.2).

It seems like a lot of instances are exactly the same, but sum types (both Generic-derived and Either) seem to have different first bytes. Which then causes TooMuchSpace errors on the ghc/server end.

[tittoassini]

I am travelling for a few days but I will have a look at this as soon as possible.

I have used flat with GHCJS but I never run the full test suite, obviously this was a mistake :-(

[tittoassini]

What is happening is that the 64 bit shiftL under ghcjs is behaving like a 32 bit rollL.

The result is that the bit that corresponds to 'Right' gets moved from the first byte '160' to the fifth byte '128'.

I will look further into it tomorrow.

[tittoassini]

Or possibly a byte begin extended to 32 rather than 64 bits.

Anyway, it should not be hard to fix.

[tittoassini]

The version of flat on github should be working now, it passes all tests.

I will make a hackage release in a few days time, in the meantime, you can refer to the github version as:

- location:
     git: https://github.com/Quid2/flat
     commit: 4795b519e2bd58127044d54b69dc371018607366
  extra-dep: true 

Let me know if it works for you.

I have tested it with this ghcjs:

resolver: lts-7.19
compiler: ghcjs-0.2.1.9007019_ghc-8.0.1
compiler-check: match-exact
setup-info:
  ghcjs:
    source:
      ghcjs-0.2.1.9007019_ghc-8.0.1:
           url: http://ghcjs.tolysz.org/ghc-8.0-2017-02-05-lts-7.19-9007019.tar.gz
           sha1: d2cfc25f9cda32a25a87d9af68891b2186ee52f9

Which version do you use?

[tysonzero]

I upgraded to GHCJS 8.4 and the existing version started working. That looks like a similar version of GHCJS to the version I was previously using, so I can check that out later. Thanks!

[tittoassini]

This sounds like bad news, the fixed version might not work with this latest compiler.

Can you give me the stack.yaml stanza for this new ghcjs compiler you are using?

[tysonzero]

I do not use stack as I find nix to be better for GHCJS development. Here is the github.json of the versions I have been using:

older:

{
  "owner": "ghcjs",
  "repo": "ghcjs",
  "rev": "eb8670c4b03b4a0ff5dd7ac3f524b410b37051ea",
  "sha256": "13s8wz9gk82cpwskc7ic3fvcpy572g87ny4icmj1apfzrrcpdp1v"
}

newer:

{
  "url": "https://github.com/ghcjs/ghcjs",
  "rev": "d20da90a4819faad1c6309a06363b34edac0374c",
  "sha256": "0jmxgfm1zwg6xscjcaycfam7zss8ik4ql4ii5lpryh4h6cdhvkbr",
  "fetchSubmodules": true
}

[tittoassini]

I have just released flat-0.3.4.

I have tested it with a few different ghcjs versions and it seems ok.