Herbert Graeber writes:
> I have found another useful application of types with value
> parameters in C++. I have seen an example of using types to check
> for proper use of physical units. I have found this very useful. But
> I haven't found a way to express this in haskell. It would be nice
> to have a type system, that supports that and similar applications.
You might be interested in the work of Andrew Kennedy on dimension
types in ML. This involves inferring polymorphic types to express
physical dimensions (mass, length, time). For higher-order
functions you get outcomes like a correct type for differentiation.
The type inference problem is harder than Hindley-Milner, as
multiplication of dimension types must be associative and
commutative. (10 kg m/s = 10 m kg/s)
Andrew J. Kennedy. Dimension Types. In ESOP '94: Proceedings of the
Fifth European Symposium on Programming, Lecture Notes in Computer
Science 788. Springer-Verlag, 1994
Available electronically from the out-of-date home page
http://www.cl.cam.ac.uk/~ajk13/
Andrew J. Kennedy. Programming Languages and Dimensions. PhD
thesis, University of Cambridge, November 1995. Also published as
Technical Report 391, University of Cambridge Computer
Laboratory.
For a copy, send email to <[EMAIL PROTECTED]>
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