Interface Files _ HOWTO?

[Simon Peyton-Jones]

Compile the module from bottom to top, with -c.  Then link.  THus

ghc -c MyList.hs
ghc -c ListFun.hs
...etc...
ghc -c Main.hs
ghc -o MyApp MyList.o ListFun.o ... Main.o

Simon

| -----Original Message-----
| From: Ingo Sander [mailto:ingo@ele.kth.se]
| Sent: 20 October 2000 17:09
| To: glasgow-haskell-users@haskell.org
| Subject: Interface Files _ HOWTO?
| 
| 
| After working a lot with Hugs I tried to compile my Haskell 
| code with GHC.
| But it does not work, I am not able to figure out how to work with the
| interface files (.hi). My program is build out of several 
| modules, like
| this (much simpler, but facing the same problem...)
| 
| File MyList.hs
| ==============
| 
| module MyList(MkList(Empty, (:-))) where
| 
| infixr 5 :-
| 
| data MkList a =   Empty
| 		| a :- (MkList a) deriving (Eq, Show)
| 
| 
| File ListFun.hs
| ===============
| 
| module ListFun(mapL) where
| 
| import MyList
| 
| mapL f Empty   = Empty
| mapL f (x:-xs) = f x :- mapL f xs
| 
| 
| 
| File ListLib
| ============
| 
| module ListLib(module MyList, module ListFun) where
| 
| import MyList
| import ListFun
| 
| 
| File Main.hs
| ============
| 
| module Main(main) where
| 
| import ListLib
| 
| main = putStr (show (mapL (+1) (1:-2:-Empty)))
| 
| 
| 
| As I said the code works with hugs, and I want to have the 
| hierarchy in
| the library structure.
| 
| So, how do I compile this in GHC? I hoped, that it would be enough to
| compile all files with the -c option (generating .hi and .o files) and
| then compiling Main.hs to get an executable program. Howeve, I get the
| following:
| 
| > ghc Main.hs
| ghc: module version unchanged at 7
| Undefined                       first referenced
|  symbol                             in file
| MyList_ZCzm_con_info                Main.o
| MyList_zdfShowMkList_closure        Main.o
| ListFun_mapL_closure                Main.o
| MyList_Empty_static_closure         Main.o
| ld: fatal: Symbol referencing errors. No output written to a.out
| 
| So, what's wrong, and am I totally on the wrong track... (I 
| studied the
| GHC User Guide, but could not find the answer to my problem).
| 
| Thanks in advance!
| 
| Ingo Sander
| 
| 
| 
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