[msla]

The kind of errors I'm interested in preventing are more like this:

    var foo = 5;

    var bar = 100;

    baz = foo + bar;

Why is that bad? Well... what do 5 and 100 mean in that program? Did you just add age in years to pixels from edge? How do you know?

Appending an integer to a string is comparatively sensible next to adding age in years to pixels from edge.

[jakevn]

Then you should not use a general numeric when you really should be using Pixel and Age types.

[msla]

My broader point is that low-level representation doesn't matter nearly as much as semantics, and yet by default type systems are obsessed with low-level representations.

Appending a number to a string is a perfectly sensible thing to do when you're displaying information to a user, yet adding two numbers or concatenating two strings could be completely senseless and proof that the development process has gone off the rails.

My dream type system is strict about semantics and only handles representation in specific circumstances. The simplest way to talk about this is in terms of units of measure: Height is a type. Whether it's in inches or centimeters is a representation. Whether that representation is a number or a string is another representation. Keeping track of whether you're showing height-in-inches or height-in-centimeters to a user is useful, but burdening your mind with whether this height-in-inches is a string or a number right now when the runtime can just as easily convert between the two is senseless, and fretting over height-in-inches versus height-in-centimeters adding person-height to shoe-sole-height to get height-in-shoes is similarly senseless.

[jakevn]

Your dream type system is out there, yet not manifest in any popular or somewhat-popular language.

I've yet to see a strictly/strongly typed language that makes this easy to do. Through some combination of plugins, esoteric languages, macros, or boilerplate, sure.

We're decades behind what is possible due to the practical.

[coldtea]

Some languages don't care either way, and will let you add those types.

[Sohcahtoa82]

> Why is that bad? Well... what do 5 and 100 mean in that program? Did you just add age in years to pixels from edge? How do you know?

You know because you should be using sensible variable names that make it obvious.