[sullyj3]

the way the impossibility is resolved is that the language itself isn't responsible for doing io, but rather it is responsible for (purely) constructing a value which represents an io computation to be performed. this value is constructed by using the bind operator to combine simpler io computation values together. that computation is then actually executed by the runtime system, which is conceptually external to the language itself. The language knows about evaluation of pure expressions, the runtime knows about execution of effectful actions.