OK, I reckon I've fixed this. You can now specify any extra C libraries on the command line (c_double.o), and they'll get linked if any TH runs happen. Simon | -----Original Message----- | From: template-haskell-admin@haskell.org [mailto:template-haskell-admin@haskell.org] On Behalf Of | André Pang | Sent: 12 May 2003 16:14 | To: template-haskell@haskell.org | Cc: chak@cse.unsw.edu.au | Subject: [Template-haskell] Calling foreign functions in a splice doesn't work | | Hi all, | | I've been trying to call a foreign function (i.e. via the FFI) inside a | splice, which doesn't seem to work. | | As an example, I'll attach a small program which does work, and then | modify it so it doesn't work. So, here's a program which does work: | | Splicer.hs: | | > module Main where | > | > import Templates | > | > main :: IO () | > main = do | > putStrLn (show ($(doubleWrapper) 5)) | | Templates.hs: | | > module Templates where | > | > import Language.Haskell.THSyntax | > | > doubleWrapper :: Expr | > doubleWrapper = [| \x -> myDouble x |] | > | > myDouble :: Int -> Int | > myDouble x = x * 2 | | Pretty simple: the program splices in an Expr named doubleWrapper; | doubleWrapper in turn calls myDouble, which is a simple function of | type Int -> Int. Execution: | | > 20:10 ~/th/ffi-bug % ghc -fglasgow-exts --make Splicer.hs | > ... | > 20:10 ~/th/ffi-bug % ./a.out | > 10 | | So that works. | | Here's a version of the program which modifies the 'myDouble' function | so that it's now a foreign C function rather than a Haskell function. | (Note that the main function and doubleWrapper functions are exactly | the same): | | SplicerFFI.hs: | | > module Main where | > | > import TemplatesFFI | > | > main :: IO () | > main = do | > putStrLn (show ($(doubleWrapper) 5)) | | TemplatesFFI.hs: | | > module TemplatesFFI where | > | > import Language.Haskell.THSyntax | > | > doubleWrapper :: Expr | > doubleWrapper = [| \x -> myDouble x |] | > | > foreign import ccall safe "c_double.h myDouble" | > myDouble :: Int -> Int | | c_double.h: | | > int myDouble (int x); | | c_double.c: | | > int myDouble (int x) | > { | > return x * 2; | > } | | Compiling the FFI version of this small program doesn't work: | | > 20:20 ~/th/ffi-bug % gcc -c c_double.c | > 20:20 ~/th/ffi-bug % ghc -fglasgow-exts --make c_double.o | > SplicerFFI.hs c_double.o | > Chasing modules from: SplicerFFI.hs | > Compiling TemplatesFFI ( TemplatesFFI.hs, ./TemplatesFFI.o ) | > Compiling Main ( SplicerFFI.hs, ./SplicerFFI.o ) | > Loading package base ... linking ... done. | > Loading package haskell98 ... linking ... done. | > Loading package haskell-src ... linking ... done. | > | > TemplatesFFI.o: unknown symbol `_myDouble' | > | > SplicerFFI.hs:7: | > Exception when trying to run compile-time code: | > Code: doubleWrapper | > Exn: | > In the first argument of `show', namely | > `($[splice]doubleWrapper 5)' | > In the first argument of `putStrLn', namely | > `(show ($[splice]doubleWrapper 5))' | > In the result of a 'do' expression: | > putStrLn (show ($[splice]doubleWrapper 5)) | | I suspect the compilation isn't working because the 'myDouble' symbol | in c_double.o isn't being loaded _at splice time_ into the list of | symbols that GHC knows about -- which is also why the exception occurs. | I've tried all sorts of kludges to convince GHC to load the symbol | from the foreign object file, like doing "ar rcs libcdouble.a | c_double.o" and then putting -L. -lcdouble on the commandline, passing | additional linker/compiler flags with -optl and -optc, etc, and none of | them have worked so far. | | This was tested with GHC on Mac OS X built from CVS 9 March 2003; my | apologies for a fairly out-of-date GHC build, but I'm having trouble | building the recent GHCs on Mac OS X. Can somebody verify that this | also occurs on Linux with a recent build of GHC, and hopefully fix it | or give me a clue on where to start looking for the bug? | | Thanks very much! | | | -- | % Andre Pang : just.your.average.bounty.hunter | | _______________________________________________ | template-haskell mailing list | template-haskell@haskell.org | http://www.haskell.org/mailman/listinfo/template-haskell