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I'm not sure I understand your last point. Do you desire for compilers to deduce the underlying type from the name of the variable or a type system that would let you create subtypes to give them additional contextual informations that the compiler would then use to enforce integrity?

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Well, actually Kawa Scheme has a feature called quantities [1]. (+ 1cm 2m) equals to 201.0cm, (+ 1cm 2degr) throws an exception (degr has to be declared first, with (define-base-unit degr "Temperature")).

To tell the truth, I’ve never found any use for this feature.

[1] https://www.gnu.org/software/kawa/Quantities.html

I'd imagine that such type/units system would be most useful in interactive use, like in WolframAlpha where the system has quite good "understanding" of units and how they should be applied to formulas.

It would be very useful in production code as well - consider the case of the Mars Climate Orbiter: http://en.wikipedia.org/wiki/Mars_Climate_Orbiter#Cause_of_f...

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