GHC Core / STG to supercombinators

Simon Peyton Jones simonpj at
Mon Apr 16 12:47:29 UTC 2018

The FloatOut pass is designed so that it can do lambda lifting for every lambda.  I think if you try
that might do it.   See CoreMonad.FloatOutSwitches, the floatOutLambdas field


From: ghc-devs <ghc-devs-bounces at> On Behalf Of Csaba Hruska
Sent: 10 April 2018 00:23
To: ghc-devs at
Subject: GHC Core / STG to supercombinators


I'd like to use GHC as a haskell frontend in a project.
I wonder what is the easiest way to compile Haskell to supercombinators (top level functions) using GHC as a library.

Is it possible to use the simplifier to transform the parsed Haskell source to supercombinators? i.e. to do

  *   eta expansion
  *   closure conversion
  *   lambda lifting
Regarding the eta expansion and lambda lifting it seems (according the comments in simplifier code) it does not guarantee to make these transformations in every case.
If GHC could transform the Core representation to supercombinators, which transformation should I use from CoreToDo?<>
I'd like to use GHC as a frontend for my custom code generator which can handle (lazy) top level functions only.
Is it better to use GHC as a library or is it better to write a compiler plugin to capture the core representation.
I do not want to optimize the Core at all neither want to use other parts of GHC's backend (i.e. codegen).
Ideally GHC would typecheck and transform everything to top level function and my system would do the rest.
Do you know what would be the easiest way to do this? (i.e. via CoreToDo or custom calls for the simplifying functions)
Or would it be simpler to generate top level (lazy) functions from STG?

Csaba Hruska
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