>> donald-balls-macbook-pro:serp dball$ sudo gem install ffi

Password:
Building native extensions.  This could take a while...
ERROR:  Error installing ffi:
	ERROR: Failed to build gem native extension.

/opt/local/bin/ruby extconf.rb
checking for ffi.h in /usr/local/include,/opt/local/include... no
checking for ffi_call() in -lffi... yes
checking for ffi_prep_closure()... yes
checking for ffi_raw_call()... no
checking for rb_thread_blocking_region()... no
creating extconf.h
creating Makefile

make
/usr/bin/gcc-4.0 -I. -I. -I/opt/local/lib/ruby/1.8/i686-darwin9 -I. -
DRUBY_EXTCONF_H=\"extconf.h\" -I/opt/local/include -D_XOPEN_SOURCE -
D_DARWIN_C_SOURCE  -I/opt/local/include -fno-common -O2  -fno-common -
pipe -fno-common  -Werror -Wunused -Wformat -Wimplicit -Wreturn-type
-c AbstractMemory.c
In file included from AbstractMemory.h:37,
                 from AbstractMemory.c:36:
Types.h:74:17: error: ffi.h: No such file or directory
In file included from Types.h:75,
                 from AbstractMemory.h:37,
                 from AbstractMemory.c:36:
Type.h:44: error: syntax error before ‘ffi_type’
cc1: warnings being treated as errors
Type.h:44: warning: no semicolon at end of struct or union
In file included from AbstractMemory.c:36:
AbstractMemory.h: In function ‘memory_get_op’:
AbstractMemory.h:115: error: dereferencing pointer to incomplete type
In file included from AbstractMemory.c:38:
Function.h: At top level:
Function.h:45: error: field ‘type’ has incomplete type
Function.h:52: error: syntax error before ‘ffi_type’
Function.h:52: warning: no semicolon at end of struct or union
Function.h:53: warning: type defaults to ‘int’ in declaration of
‘ffiParameterTypes’
Function.h:53: warning: data definition has no type or storage class
Function.h:54: error: syntax error before ‘ffi_cif’
Function.h:54: warning: type defaults to ‘int’ in declaration of
‘ffi_cif’
Function.h:54: warning: data definition has no type or storage class
Function.h:59: error: syntax error before ‘abi’
Function.h:59: warning: type defaults to ‘int’ in declaration of ‘abi’
Function.h:59: warning: data definition has no type or storage class
Function.h:66: error: syntax error before ‘}’ token
make: *** [AbstractMemory.o] Error 1


Gem files will remain installed in /opt/local/lib/ruby/gems/1.8/gems/
ffi-0.5.4 for inspection.
Results logged to /opt/local/lib/ruby/gems/1.8/gems/ffi-0.5.4/ext/
ffi_c/gem_make.out

donald-balls-macbook-pro:serp dball$ ruby -v
ruby 1.8.7 (2008-08-11 patchlevel 72) [i686-darwin9]