[Haskell-cafe] Anonymous FFI calls

[Simon Peyton Jones]

| Thanks to everyone who replied!
| 
| It seems like that through a combination of facilities like `libffi'
| and `addTopDecls' I can do everything that I wanted to do.

Great.  But please, please, do write up what you learned on the FFI wiki page
	https://wiki.haskell.org/GHC/Using_the_FFI

Simon

| -----Original Message-----
| From: Francesco Mazzoli [mailto:f at mazzo.li]
| Sent: 12 February 2015 09:00
| To: Simon Peyton Jones
| Cc: Michael Sloan; Manuel Chakravarty; Geoffrey Mainland
| (mainland at cs.drexel.edu); ghc-devs at haskell.org; haskell
| Subject: Re: [Haskell-cafe] Anonymous FFI calls
| 
| Thanks to everyone who replied!
| 
| It seems like that through a combination of facilities like `libffi'
| and `addTopDecls' I can do everything that I wanted to do.
| 
| I still want to take a shot at implementing anonymous FFI calls, since
| IMHO I think they are a very small but useful addition to the
| language.
| 
| Francesco
| 
| On 12 February 2015 at 09:29, Simon Peyton Jones <simonpj at microsoft.com>
| wrote:
| > |  Also, I meant to say that addTopDecls is only exported by
| > |  "Language.Haskell.TH.Syntax".  While this is a digression, there are
| a
| > |  few other handy functions that are oddly left out of
| > |  "Language.Haskell.TH": addDependentFile, addModFinalizer, and
| possibly
| > |  more.
| >
| > That does seem wrong.  Do make a patch!
| >
| > SIMon
| >
| > |
| > |  -Michael
| > |
| > |  On Wed, Feb 11, 2015 at 3:25 PM, Simon Peyton Jones
| > |  <simonpj at microsoft.com> wrote:
| > |  > I would LOVE someone to improve the documentation for addTopDecls.
| > |  Manuel Chakravarty and Geoff Mainland were responsible for the
| > |  implementation.
| > |  >
| > |  > Simon
| > |  >
| > |  > | -----Original Message-----
| > |  > | From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf
| Of
| > |  > | Michael Sloan
| > |  > | Sent: 11 February 2015 23:19
| > |  > | To: Francesco Mazzoli
| > |  > | Cc: ghc-devs at haskell.org; haskell
| > |  > | Subject: Re: [Haskell-cafe] Anonymous FFI calls
| > |  > |
| > |  > | It seems like addTopDecls[1] will able to help here.
| > |  Unfortunately,
| > |  > | the function is not well documented and not very discoverable
| > |  > | because it's only exported by Language.Haskell.TH.
| > |  > |
| > |  > | The documentation doesn't mention that it can only be used to
| > |  create
| > |  > | new top level functions and FFI imports[2].  I think that adding
| > |  FFI
| > |  > | imports was the main motivation for implementing it.   In the
| past
| > |  > | I've wanted to generate instances via this function, but
| > |  > | unfortunately it's not implemented..
| > |  > |
| > |  > | Hope that helps!
| > |  > | -Michael
| > |  > |
| > |  > | [1] http://hackage.haskell.org/package/template-haskell-
| > |  > | 2.9.0.0/docs/Language-Haskell-TH-Syntax.html#v:addTopDecls
| > |  > |
| > |  > | [2]
| > |  > |
| > |  https://github.com/ghc/ghc/blob/1d982ba10f590828b78eba992e73315dee33
| > |  > | f78a/
| > |  > | compiler/typecheck/TcSplice.hs#L818
| > |  > |
| > |  > | On Wed, Feb 11, 2015 at 2:26 AM, Francesco Mazzoli <f at mazzo.li>
| > |  wrote:
| > |  > | > Hi,
| > |  > | >
| > |  > | > I am in a situation where it would be very useful to call C
| > |  > | > functions without an explicit FFI import.  For example, I'd
| like
| > |  > | > to be able to do
| > |  > | >
| > |  > | >     (foreign import ccall "cadd" :: CInt -> CInt -> CInt) 1 2
| > |  > | >
| > |  > | > instead of declaring the foreign import explicitely at the top
| > |  level.
| > |  > | >
| > |  > | > Is there a way to do this or to achieve similar results in
| some
| > |  > | > other way?
| > |  > | >
| > |  > | > If not, I imagine it would be easy to implement such a
| facility
| > |  in
| > |  > | > GHC, given that the code implementing calling to C functions
| > |  must
| > |  > | > already be present to implement "proper" FFI imports.  I think
| > |  > | > such an addition would be useful in many cases.
| > |  > | >
| > |  > | > Thanks,
| > |  > | > Francesco
| > |  > | > _______________________________________________
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