> Are you familiar with the idea of "making illegal states unrepresentable", and "parse, don't validate"? I haven't heard of those concepts/ideas before. Thank

> Are you familiar with the idea of "making illegal states unrepresentable", and "parse, don't validate"? I haven't heard of those concepts/ideas before. Thanks for linking the article to define those concepts. With your example, and the article mentioning that "parsing should take place at the boundaries" (paraphrase), I can see how types (a la ML families) can be defined and composed give internal coherence once an external input has been parsed and hence validated. Really interesting approach which I haven't considered before!