Re: Remote GHCi

Ok, it seems that (1) is easy to support in a remote GHCi, (2) is not, and (3) I'm not sure about. GHCi itself does something very similar to (3): when we compile a statement it becomes a value of type IO [HValue], that we can evaluate and get back a list of the values that were bound to variables by the statement. In remote GHCi I can support this by having an RPC to evaluate the IO action and the returned HValues are remote references (StablePtrs) to values in the interpreter context. In any case I don't plan to break anything unless we have alternative ways to support everything without major upheaval. In the meantime there will probably be a flag to select remote GHCi, and existing use cases will continue to be supported. Cheers Simon On 17/11/2015 17:11, Andrew Gibiansky wrote:

Simon,

As Sumit said, we use dynCompileExpr for core functionality of IHaskell. I am not really sure how the change you are proposing affects that, though.

We use dynCompileExpr in several places for evaluation inside the interpreter context:

1. Evaluating a Haskell expression in the interpreter context, converting the result to a ByteString, then using fromDynamic to extract the bytestring and convert it to a value in the compiled context. 2. Getting a file handle from the interpreter context to the compiled context; this does not actually use dynCompileExpr because there were some bugs with dynCompileExpr and so I had to literally copy source from InteractiveEval to reimplement parts of dynCompileExpr (unrelated: the issue was that dyncompileexpr imported and then unimported Data.Dynamic, and this messed with data declarations that had already been created in the interpreter context) 3. Extracting IO a values from the interpreted context to the compiled context so that they could be run; this is necessary to get displayed values from the interpreter back to the compiled code.

I think two of our uses, which are both very central to the way IHaskell works, would be impacted by requiring a Binary instance (or similar), which is what I think you are proposing (since we have two uses at least where we marshall `IO x` values via dynCompileExpr, which cannot be serialized, I believe.)

I am sure that there are alternative ways to do what we are doing, but they are probably not simple and would take quite a bit of work.

-- Andrew

On Tue, Nov 17, 2015 at 6:29 AM, Richard Eisenberg mailto:eir@cis.upenn.edu> wrote:

How does this interact with typechecker plugins? I assume they would still happen in GHC's process.

I've also been thinking about designing and implementing a mechanisms where programmers could specify custom pretty-printers for their types, and GHC would use these pretty-printers in error messages. This action would also probably need to be in the same process.

Would either of these ideas be affected? My guess is "no", because we should be able to be selective in what gets farmed out to the second process and what stays locally.

Richard

On Nov 17, 2015, at 5:10 AM, Simon Marlow mailto:marlowsd@gmail.com> wrote:

> Hi folks - I've been thinking about changing the way we run interpreted code so that it would be run in a separate process. It turns out this has quite a few benefits, and would let us kill some of the really awkward hacks we have in GHC to work around problems that arise because we're running interpreted code and the compiler on the same runtime. > > I summarised the idea here: https://ghc.haskell.org/trac/ghc/wiki/RemoteGHCi > > I'd be interested to hear if anyone has any thoughts around this, particularly if doing this would make your life difficult in some way. Are people relying on dynCompileExpr for anything? > > Cheers, > Simon > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org mailto:ghc-devs@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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