The Many Faces of D - slides
Simen kjaeraas
simen.kjaras at gmail.com
Sun Oct 3 08:21:33 PDT 2010
Simen kjaeraas <simen.kjaras at gmail.com> wrote:
> Russel Winder <russel at russel.org.uk> wrote:
>
>> def sumOfSquares ( sequence ) :
>> return sum ( [ item * item for item in sequence ] )
>> So the question is whether there is an idiomatic D version of this.
>
> Probably this:
>
> auto sum( R )( R range ) {
> return reduce!"a+b"( 0, range );
> }
>
> auto sumOfSquares( R )( R range ) {
> return sum( map!"a*a"( range ) );
> }
>
> I have written an implementation of list
> comprehensions for D, but it is not perfect.
>
> Usage example:
> ( list!"2 * a" | [1,2,3,4,5] & where!"a & 1" )
>
> "2 * a" and "a & 1" may be replaced by any callable or a string
> mixin, just like functions in std.algorithm.
> [1,2,3,4,5] may be replaced with any range.
>
> This is actually two parts, so the following are also allowed
> usages:
>
> ( list!"2 * a" | [1,2,3] )
> ( [1,2,3] & where!"a & 1" )
>
> Using this, the solution to the above would be:
>
> auto sum( R )( R range ) {
> return reduce!"a+b"( 0, range );
> }
>
> auto sumOfSquares( R )( R range ) {
> return sum( list!"a*a" | range );
> }
Sorry, code was wrong. Update:
module listcomp;
import std.algorithm;
import std.range;
import std.array;
struct List( alias pred ) {
auto opBinary( string op : "|", Range )( Range other ) {
return map!pred(other);
}
}
struct Where( alias pred ) {
auto opBinaryRight( string op : "&", R )( R range ) {
return filter!pred(range);
}
}
@property
auto where( alias pred )( ) {
Where!pred result;
return result;
}
@property
auto list( alias pred )( ) {
List!pred result;
return result;
}
unittest {
assert( equal( ( list!"2 * a" | [1,2,3,4,5] & where!"a & 1" ),
[2,6,10] ) );
assert( equal( ( list!"2 * a" | [1,2,3] ), [2,4,6] ) );
}
--
Simen
More information about the Digitalmars-d
mailing list