• bearophile (28/28) May 06 2014 Is it a good idea to add a function like this to Phobos?

"bearophile" <bearophileHUGS lycos.com> writes:

Is it a good idea to add a function like this to Phobos?

This is just a first draft of the idea.


void main() {
     import std.stdio, std.algorithm, std.range, range_matcher;

     auto primes = iota(2, uint.max)
                   .filter!(x => iota(2, x)
                                 .all!(t => x % t != 0));

     auto twinPrimes = primes.rangeMatch!(q{x, x + 2},
                                          q{ [x, x + 2] });
     twinPrimes.take(20).writeln;

     immutable arr = [1, 2, 1, 3, 5, 3];
     // All items of arr that appear twice or more:
     arr.rangeMatch!(q{x, $_, x}, q{ x }).writeln;
}


Output:

[[3, 5], [5, 7], [11, 13], [17, 19], [29, 31], [41, 43], [59, 
61], [71, 73], [101, 103], [107, 109]]
[1, 3]


rangeMatch takes three arguments, the first is a range of items. 
The second is a string that encodes what to match, and the third 
is a string that generates the output from the matched data.

So q{x, x + 2} matches any value x followed by x + 2. This is the 
definition of twin prime, if the input sequence is of primes.


q{x, $__, x} matches any x, followed by 1 or more other items, 
followed by the same x.
$_ means 0 or more.

Bye,
bearophile