In order to use the callbacks, I need to write a pragma in the Callback class for the signature. My signature is something like (where ulong means pointer) void (ulong ulong long long ulong) Can you help me ? Here is an example for another signature : !Callback methodsFor: 'signatures' stamp: 'eem 11/1/2010 16:40'! intcharstarRetint: callbackContext sp: spAlien <signature: 'int (*)(int, char *)' abi: 'IA32'> ^callbackContext wordResult: ((block value: (spAlien signedLongAt: 1) ~= 0 value: (Alien forPointer: (spAlien unsignedLongAt: 5)) strcpyUTF8) ifNil: [0] ifNotNil: [:result| result isInteger ifTrue: [result] ifFalse: [result == true ifTrue: [1] ifFalse: [0]]])! !