>From what you say, in a subsequent message, about the strictness being "b",
>that means the strictness analyser has decided that $fNumFixed2 is bottom
>(i.e. diverges). So there's no point in exposing the unfolding, because (one
>way or another) it's an infinite loop, so there's no point in optimising it.
It's unusual to have a bottom dictionary; you must be using undecidable
instances or something. ("Scrap your boilerplate with class" describes why
recursive dictionaries are good.) Bur apparently you have.
It's arguable that with -fexpose-all-unfoldings we should expose even bottom
values. If you have a reason for wanting that, it'd be an easy change to make,
I think.
Simon
| -----Original Message-----
| From: Glasgow-haskell-users [mailto:glasgow-haskell-users-
| boun...@haskell.org] On Behalf Of Christiaan Baaij
| Sent: 26 March 2014 16:41
| To: glasgow-haskell-users
| Subject: GHC API: getting the unfolding of a "strange" Id
|
| Dear list,
|
| I'm using the GHC API to get Core Expressions from haskell interface
| (.hi) files, and have encountered a strange kind of 'Id' for which I
| can't seem to get the unfolding:
|
| The properties of this 'Id' are the following:
| - varName: $fNumFixed2
| - IdDetails: VannillaId
| - Pretty print of IdInfo.inlinePragInfo: [Always]
| - IdInfo.unfoldingInfo: NoUnfolding
|
| The source file which gives rise to this 'Id' is:
| https://github.com/christiaanb/clash-
| prelude/blob/master/src/CLaSH/Sized/Fixed.hs
| As you can see, the file is compiled with: -fexpose-all-unfoldings
|
| The '$f' prefix seems to indicate that the 'Id' is a Dictionary Function,
| so I was expecting its 'IdInfo.unfoldingInfo' to be a 'DFunUnfolding'.
| Given that pretty printing 'inlinePragInfo' gives me '[Always]', I would
| expect to have a usable 'Unfolding' in general.
| How can GHC inline the body of this 'Id' if it has no unfolding?
|
| Also, if I compile the file with "-O0 -fno-omit-interface-pragmas", the
| $fNumFixed2 'Id' is no longer included in the interface file.
| At positions where "$fNumFixed2" was originally used, a equality
| constraint can eventually be found:
|
| Using -O:
| (CLaSH.Sized.Fixed.$fNumFixed2
| @(GHC.TypeLits.+ 4 4)
|
| Using -O0 -fno-omit-interface-pragmas:
| (GHC.Types.Eq#
| @GHC.Types.Bool
| @(GHC.TypeLits.<=? 1 (GHC.TypeLits.+ 4 4))
| @GHC.Types.True
| _CO_)
|
| So my question is, what kind of "strange" 'Id' is this $fNumFixed2?
| And how can I get the Core expression for this 'Id' from the interface
| file?
| And if I can't get it from the interface file, is there a straightforward
| way to generate it from the 'Id'?
|
| Cheers,
|
| Christiaan
|
|
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