Permutate parsers, don't validate

“Parse, don’t validate” has been one of my favourite programming articles for some time. The main gist of the article is that, when writing in a type-driven fashion, your snappy slogan should be: Parse, don’t validate. The core difference between parsing and validating can be explained by looking at two very similar functions: parseInt :: String -> Maybe Int parseInt str = Text.Read.readMaybe str