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>If you can't keep the "types" of your design in your head, your design might be broken.

Either that, or you might not work on toy projects.

Less aggressively, you may also be inheriting someone else's design.

Granted it's difficult to remember the type of the casual e-mail address or of a list of integers. In Haskell, where there are a thousand ways of encoding the most trivial things, that is.

In my own practice, most transformations don't involve relations over more than 5 variables with mostly obvious types. Yes, this is hard to use:

https://tronche.com/gui/x/xlib/window/XCreateWindow.html

But then 1) there might be nicer ways to design an API and 2) at these few places the implementor of the API can just insert value assertions.

>Granted it's difficult to remember the type of the casual e-mail address or of a list of integers.

It would be a toy project that only (or mainly) has those as all the types you need to remember -- so that just proves my point.

Also the 'type' of an email address is an unsolved problem -- if we're talking type checking. It's not a string, and it's not solvable with regex either. So bad example all around.

This is the point. Encode email addresses as strings and be done. Not a problem in practice.

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