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()

	get_filename_component(lib ${CMAKE_CURRENT_SOURCE_DIR} NAME)
	string(REGEX REPLACE "-" "_" lib ${lib})

	list(GET implementations 0 default)
	
	if ("${prefix}" STREQUAL "")
		set(prefix "")
	else()
		set(prefix "${prefix}_")
		string(REGEX REPLACE "/" "_" prefix ${prefix})
	endif()
	
	
	set(${lib}_${prefix}implementations ${implementations} PARENT_SCOPE)
	set(${lib}_${prefix}implementation "${default}" CACHE STRING "${lib} implementation chosen at configure time")
	set_property(CACHE ${lib}_${prefix}implementation PROPERTY STRINGS ${implementations})

endfunction(DefineImplementations)