Presumably the idea is that you can prevent your site having broken internal links by constructing links with data types and checking the links when creating them at compile time. You could actually do something similar in most languages, even dynamic ones, so I don't see what is specific to haskell about it, e.g. rails has link_to and friends which require you to have a route set up in order to link to it (though not compile time). Golang has similar protection for XSS and reverse routes on routers if you require it so again not specific to Haskell.

Clearly you won't be able to prevent (nor would you want to) links like yours above from being a 404, so perhaps no more internal 404s would be more accurate.