[justinpombrio]

You understand it. It's using the word "parse" metaphorically, to mean "validate, then put it in a specially marked data structure". For example, `parse_int :: string -> maybe int` is a parsing function, and it "validates that the string is an integer, then puts it in a specially marked data structure called int". However, the post uses the word "parse" not only for true parsing functions (that convert text into a data structure), but also for conversions from data structure to data structure.

I also find this a confusing use of the word "parse", and it's not explained in the post, and I think "parse, don't validate" is a poor slogan as a result. The traditional slogan is "make illegal states unrepresentable", though that's a bit narrower of a concept.

[b3morales]

I don't think this is the same as "make illegal states unrepresentable"; it's a corollary (or the converse maybe):

"Make assertions of legal states representable"

[joshuamorton]

They're sort of the same. If you have str and safestr, and safestr is known to confiorm to some invariant, the illegal state of a, say str where validate hasn't been called, isn't representable.