Re: Constructor wrappers vs workers in generated Core

Sorry, here's my explanation. In summary, I was trying to go for the cleanest, tidiest, simplest AST possible for interpretation. My long-term goal is to have a slow but working interpreter of GHC Haskell written in Haskell that is capable of hot-swapping without segfaulting, by gracefully handling changing types and functions (just report a type error like the Lisps do), and the short-term goal is to export that interpretable AST as a web service so that a simple JS interpreter and/or substitution stepper could be written for the purposes of education, like https://chrisdone.com/toys/duet-delta/. I think this mailing list thread turns out to be an x/y problem. I need STG. I ended up doing lots of cleaning steps to generate a more well-formed Core. I learned that the Core that comes from the desugarer is incomplete and realized today that I was duplicating work done by the transformation that converts Core to STG. I'd initially avoided STG, thinking that Core would suffice, but it seems that STG is the AST that I was converging on anyway. It seems that STG will have all class methods generated, wrappers generated (and inlined as appropriate), primops and ffi calls are saturated, etc. no Types or coercions, etc. It even has info about whether closures can be updated and how. I wish I'd chosen STG instead of Core from the beginning, but it doesn't set me back by much so I'll consider this a learning exercise. If anything, it makes me appreciate almost everything going on in STG for why it's there and is useful. I'm aware of two projects that interpret their own form of STG: http://hackage.haskell.org/package/stgi http://hackage.haskell.org/package/ministg But I intend on consuming directly the STG AST from GHC. The bulk of the work I did that will stay useful is managing a global mapping of Ids, in terms of global, local ids, and conids in separate namespaces. IOW I replace all Ids in the AST with a globally unique Int, like Unique, but it preserves across separate runs, rather than being per GHC run. So I can plug that work into the STG AST instead. I have a Docker file that compiles a patched GHC and outputs my AST for ghc-prim, integer-gmp and base, that leads to all these files: https://gist.github.com/chrisdone/5ed9adf9dba5fd82d582e9f2bbc30c9f which have Ids that reference eachother cross-module/package without any need for more fiddling/munging. The AST looks like this https://github.com/chrisdone/prana/blob/eaa5b2111631c13eb6b41c9a47400a4ba6a0... then I have a mapping from Int64->Name for debugging. I think having an STG representation that tools like ministg/stgi can consume that includes everything (ghc-prim, integer-gmp and base) is handy, aside from my own use-cases (giving the AST to a web app and "real" interpreting). Cheers! On Mon, 4 Feb 2019 at 17:56, Matthew Pickering wrote:

If you want your core to look at much like the source program as possible then you could print `$WFoo` as just `Foo`?

The existence of wrappers is a crucial part of desugaring so perhaps it's useful for users to see them in the output of your program if it's intended to be educational?

Matt

On Sat, Feb 2, 2019 at 3:06 PM Christopher Done wrote:

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On Sat, 2 Feb 2019 at 14:50, Matthew Pickering wrote:

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There is no way to turn off wrappers and I don't think it would be possible to implement easily if at all.

Fair enough.

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However, they will all probably be inlined after the optimiser runs but it seems that you don't want to run the optimiser at all on the generated core?

Yeah, I'm trying to avoid as much instability in the output shape as possible, and for educational purposes, optimizations make fairly readable code unreadable.

Wait. Can I rely on case alt patterns having the same arity as the original user-defined data type before optimization passes are run?

If the answer to that is yes, then I could just replace all wrapper calls with worker calls, which is an easy enough transformation. As a precaution, I could add a check on all case alt patterns that the arity matches the worker arity and barf if not.

Thanks for your help!

Chris