Are there any languages that allow units?

You might be interested in F# Units of Measure support

F# has units of measure. Some examples from

http://blogs.msdn.com/andrewkennedy/archive/2008/08/20/units-of-measure-in-f-part-one-introducing-units.aspx

Well the ActiveSupport library for ruby extends the Integer class with methods like hours and days which allows you to write things like:

Time.now + 5.days

But that's not really a syntax feature - it's just a method call and is possible in any language that allows you to add methods to an existing class. You could do it in C# with extension methods - though it would have to be 5.days() there.

There is a Boost C++ library for Units that makes extensive use of template metaprogramming to provide something similar to the syntax you desire.

quantity<force>     F(2.0*newton);
quantity<length>    dx(2.0*meter);
quantity<energy>    E(work(F,dx));

http://www.boost.org/doc/libs/1_37_0/doc/html/boost_units.html