Re: Higher-order functions?

[Timon Gehr]

On 04/11/2012 11:37 AM, Xan wrote:

On Wednesday, 11 April 2012 at 09:17:12 UTC, Jacob Carlborg wrote:

On 2012-04-11 10:45, Xan wrote:

Good answer.

For the other hand, what is the simplest method for implementing this
(in pseucode) in D:

Sure:

FUNC someprocedure(int a, int b, func<int, int: int> f) int
RETURN f(a, b)
}

And call it with:

IO.writeLine("add: " .. someprocedure(2, 3, { a, b => a + b }))
IO.writeLine("multiply: " .. someprocedure(2, 3, { a, b => a * b }))

(Read the => as "gives")

Is it possible to have this?

If I understand the above code correctly:

import std.stdio;

int someprocedure (int a, int b, int delegate (int, int) f)
{
    return f(a, b);
}

Yes, you undertood correcty.

Your code gives me an error:

$ gdmd-4.6 funcions.d
funcions.d:10: expression expected, not '>'
funcions.d:10: found 'a' when expecting ','
funcions.d:11: expression expected, not '>'
funcions.d:11: found 'a' when expecting ','

void main ()
{
    writeln("add: ", someprocedure(2, 3, (a, b) => a + b));
    writeln("multiply: ", someprocedure(2, 3, (a, b) => a * b));
}

AFAIK GDC does not yet support the new lambda literal syntax.

You can use

void main ()
{
    writeln("add: ", someprocedure(2, 3, (a, b) { return a + b; }));
    writeln("multiply: ", someprocedure(2, 3, (a, b) { return a * b; }));
}