Property definitions

nitc $ AbstractCompilerVisitor :: value_instance
	fun value_instance(object: Object): RuntimeVariable
	do
		if object isa Int then
			return int_instance(object)
		else if object isa Bool then
			return bool_instance(object)
		else if object isa String then
			return string_instance(object)
		else
			abort
		end
	end
src/compiler/abstract_compiler.nit:1833,2--1844,4