PUBLIC
Please see this question in my previous email:
* Unfortunately, I am unable to reproduce this from the command line using
the GHC executable, so before I put in the effort of making a minimal example
of using the GHC API to get this result, I would first like to know if this is
even an interesting case, or if there is some explanation for why one of these
two would have an unfolding when the other doesn't, in certain cases.
So I can NOT reproduce it with just a GHC command line, only with my program
(that uses GHC as a library). So it will require extra effort to get something
you or others can just run, hence my question: is there anything here that is
worth pursuing at all? Or who cares, since I'm not using unfoldings anymore
(I've switched over to storing IfaceExprs directly), and it works in
GHC-the-program?
From: Simon Peyton Jones <simon.peytonjo...@gmail.com>
Sent: Wednesday, April 6, 2022 3:37 PM
To: Erdi, Gergo <gergo.e...@sc.com>
Cc: Gergo Érdi <ge...@erdi.hu>; GHC Devs <ghc-devs@haskell.org>;
clash-langu...@googlegroups.com
Subject: [External] Re: Avoiding `OtherCon []` unfoldings, restoring
definitions from unfoldings
Hi Gergo
If you think GHC has a but, can you open a ticket about this? It's all
getting lost in a maze of emails.
Can you also give precise repro instructions? In an attempt to reproduce, I
have just compiled this module (the code you gave)
{-# OPTIONS_GHC -fexpose-all-unfoldings #-}
module Foo where
nonEmptySubsequences :: [a] -> [[a]]
nonEmptySubsequences [] = []
nonEmptySubsequences (x:xs) = [x] : foldr f [] (nonEmptySubsequences xs)
where
f ys r = ys : (x:ys) : r
subsequences :: [a] -> [[a]]
subsequences xs = [] : nonEmptySubsequences xs
with HEAD, and -O. Unlike you, I see both unfoldings in the interface file.
So clearly you and I are doing different things -- but I can't work out what is
different without more precision about what you are doing. (It would be
harder if it only happens when you use GHC as a library, but I think you are
seeing this behaviour in regular GHC.)
Thanks
Simon
On Wed, 6 Apr 2022 at 03:05, Erdi, Gergo
<gergo.e...@sc.com<mailto:gergo.e...@sc.com>> wrote:
PUBLIC
Just so this isn't prematurely all lost, I went back and looked for this
example. With the following two definitions:
subsequences :: [a] -> [[a]]
subsequences xs = [] : nonEmptySubsequences xs
nonEmptySubsequences :: [a] -> [[a]]
nonEmptySubsequences [] = []
nonEmptySubsequences (x:xs) = [x] : foldr f [] (nonEmptySubsequences xs)
where f ys r = ys : (x : ys) : r
If I save the interface, load it back and look at the unfoldings, I see that
`subsequences` has a useful unfolding:
subsequences Unf{Src=<vanilla>, TopLvl=True, Value=True,
ConLike=True, WorkFree=True, Expandable=True,
Guidance=IF_ARGS [0] 30 10}
Whereas `nonEmptySubsequenes` has a trivial one:
nonEmptySubsequences OtherCon []
The interface I save is created from the ModDetails returned by tidyProgram.
ExposeAllUnfoldings is set.
Unfortunately, I am unable to reproduce this from the command line using the
GHC executable, so before I put in the effort of making a minimal example of
using the GHC API to get this result, I would first like to know if this is
even an interesting case, or if there is some explanation for why one of these
two would have an unfolding when the other doesn't, in certain cases.
-----Original Message-----
From: ghc-devs
<ghc-devs-boun...@haskell.org<mailto:ghc-devs-boun...@haskell.org>> On Behalf
Of Gergo Érdi
Sent: Saturday, April 2, 2022 11:31 AM
To: Simon Peyton Jones
<simon.peytonjo...@gmail.com<mailto:simon.peytonjo...@gmail.com>>
Cc: GHC Devs <ghc-devs@haskell.org<mailto:ghc-devs@haskell.org>>;
clash-langu...@googlegroups.com<mailto:clash-langu...@googlegroups.com>
Subject: [External] Re: Avoiding `OtherCon []` unfoldings, restoring
definitions from unfoldings
I'm using Prep's output (mostly so that it's in ANF) in my full compilation
pipeline, so ideally I would save Prep'd Core in my .hi-equivalents so that I
don't have to rerun Prep on them every time I use them.
I'll get back to you with some concrete examples of `OtherCon []` vs.
meaningful unfoldings next week.
Merging with my other question about shadowing problems with `toIface*`, in
summary it seems that what I really should be doing, is compiling up to Tidy,
taking the `CoreBinding`s from there and using `toIfaceBinding` on them to save
the definitions.
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