The ERROR statement is provided to mark error conditions on the code level. Usually this is used to mark sections in the code that are not implemented or that should not be reached during execution. The resulting error output then includes also the source code file, line number and function in which the error occurred. As such, this is meant for developers to mark and debug their code, not for errors to be presented to end users. The ERROR keyword expects one parameter, which is a string literal (you cannot use variables or dynamically constructed strings). The following is a commonly used sample:

IFDEF("target_android") {
	// Android implementation
}
ELSE IFDEF("target_iosoc") {
	// iOS Objective-C implementation
}
ELSE {
	ERROR("Not implemented")
}