On 2018-02-18 22:55, Paul Rubin wrote:
Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> writes:
"positive odd integers greater than 10 but less than 15003 divisible by
17 except for 850, 867 and 1394; or primes that aren't Mersenne
primes"....
It *could* be a type, if your type system was sufficiently flexible to
allow you to specify something in that level of detail. Of course no
existing type system is.
Of course dependent types could do that (they have a type for every
proposition in constructive predicate calculus). You might also be able
to do it with Liquid Haskell's refinement types, though automatically
checking them might not be so easy.
That's an easy one: even Pascal in the 1970s could deal with enumerated
types like the values 1, 3, 5, 7, 9. (I think.)
Idunno about Pascal, but Ada has integer range types.
Back in the early 1980s, I took a few courses involving Pascal,
and it certainly supported subranges then. Quoting from my
text[1]:
A _scalar subrange_ data type is a data type composed of
a specified range of any of the other standard or user-
defined scalar types, except type REAL.
We define a subrange type with a TYPE declaration of the
following format.
TYPE type-name = lowerlimit..upperlimit;
[...]
Examples of subrange declarations are:
TYPE EXAMSCORES = 0..100;
Of course, Pascal being Pascal, a function to return the sum
of an array of INTEGER would refuse to return the sum of an
array of EXAMSCORES.[2]
[1] _An Introduction to Programming and Problem Solving With
Pascal_; Schneider, Weingart, and Perlman; (C) 1978
[2] Kernighan examines a similar issue in Section 2.1 of
"Why Pascal is Not My Favorite Programming Language",
<http://www.cs.virginia.edu/~cs655/readings/bwk-on-pascal.html
--
Michael F. Stemper
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