# Try to load a module AST using a path.
	# Display an error if there is a problem (IO / lexer / parser) and return null
	#
	# The AST is loaded as is total independence of the model and its entities.
	#
	# AST are not cached or reused thus a new AST is returned on success.
	fun load_module_ast(filename: String): nullable AModule
	do
		if not filename.has_suffix(".nit") then
			self.toolcontext.error(null, "Error: file `{filename}` is not a valid nit module.")
			return null
		end
		if not filename.file_exists then
			self.toolcontext.error(null, "Error: file `{filename}` not found.")
			return null
		end

		self.toolcontext.info("load module {filename}", 2)

		# Load the file
		var file = new FileReader.open(filename)
		var lexer = new Lexer(new SourceFile(filename, file))
		var parser = new Parser(lexer)
		var tree = parser.parse
		file.close

		# Handle lexer and parser error
		var nmodule = tree.n_base
		if nmodule == null then
			var neof = tree.n_eof
			assert neof isa AError
			error(neof, neof.message)
			return null
		end

		return nmodule
	end