3.5. Re-directing the compilation output(s)

GHC's compiled output normally goes into a .hc, .o, etc., file, depending on the last-run compilation phase. The option -o foo re-directs the output of that last-run phase to file foo.

Note: this “feature” can be counterintuitive: ghc -C -o foo.o foo.hs will put the intermediate C code in the file foo.o, name notwithstanding!

EXOTICA: But the -o option isn't of much use if you have several input files… Non-interface output files are normally put in the same directory as their corresponding input file came from. You may specify that they be put in another directory using the -odir <dir> (the “Oh, dear” option). For example:

% ghc -c parse/Foo.hs parse/Bar.hs gurgle/Bumble.hs -odir `arch`

The output files, Foo.o, Bar.o, and Bumble.o would be put into a subdirectory named after the architecture of the executing machine (sun4, mips, etc). The directory must already exist; it won't be created.

Note that the -odir option does not affect where the interface files are put. In the above example, they would still be put in parse/Foo.hi, parse/Bar.hi, and gurgle/Bumble.hi.

MORE EXOTICA: The -osuf <suffix> will change the .o file suffix for object files to whatever you specify. (We use this in compiling the prelude.). Similarly, the -hisuf <suffix> will change the .hi file suffix for non-system interface files (see Section 3.7.3).

The -hisuf/-osuf game is useful if you want to compile a program with both GHC and HBC (say) in the same directory. Let HBC use the standard .hi/.o suffixes; add -hisuf g_hi -osuf g_o to your make rule for GHC compiling…

FURTHER EXOTICA: If you are doing a normal .hs-to-.o compilation but would like to hang onto the intermediate .hc C file, just throw in a -keep-hc-file-too option. If you would like to look at the assembler output, toss in a -keep-s-file-too, too.