function(DefineImplementations prefix)

	FILE(GLOB children RELATIVE ${CMAKE_CURRENT_SOURCE_DIR}/${prefix} ${CMAKE_CURRENT_SOURCE_DIR}/${prefix}/*)

	set(implementations "")
	foreach(child ${children})
		IF(IS_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/${prefix}/${child})
		    LIST(APPEND implementations ${child})
		ENDIF()
	ENDFOREACH()

	list(LENGTH implementations nr_implementations)

	if(nr_implementations EQUAL 0)
		message(FATAL_ERROR "Cannot call DefineImplementations with an empty implementations list.")
	endif()

	list(GET implementations 0 default)
	set(${prefix}_implementations ${implementations} PARENT_SCOPE)
	set(${prefix}_implementation "${default}" CACHE STRING "${prefix} implementation chosen at configure time")
	set_property(CACHE ${prefix}_implementation PROPERTY STRINGS ${implementations})

endfunction(DefineImplementations)