Hi everybody.

I am tring to use a function where its parameter is another function, and at the same time are both already made - they cannot be modified - and the second one has to be conditioned before to be passed as argument.

Let's say I have these function and I cannot modify:

-jac(+d) that works on function and return real

real jac(real function(real) fun, real x) {return d(fun, x);}
real d(real function(real) fun, real x) {return fun(x);}

-F1 that works on two reals and return real

real F1(real a, real b) {return a + b;}

So I need a way to condition F1 fixing b and then pass it to jac as argument.

To do that I've created a delegate 'simp' conditionig F1:

real delegate(real) simp(real function(real, real) f, real x) {
	real _simp(real z) {
		return f(z, x);
		}
	return &_simp;
	}
(here 'simp' fixes b at x).

My main is:

void main() {
	real x_n = 1;
	real x_m = -1;
	real delegate(real) s_n = simp(&F1, x_n);
	//auto J = jac(s_n, x_m); //Error: function app.jac (real function(real) fun, real x) is not callable using argument types (real delegate(real), real)
	}

the code fails because jac expect as argument a function but I found only a delegate to obtain a simplified function without any touch at already made functions jac, d and F1.

There is a clean way to make it possible? I mean: without to touch (neither rewrite) jac, d and F1, obtain simplied F1 to pass to jac.

Thaks in advance to anyone could help me.
Luigi

On Friday, 1 May 2015 at 03:34:53 UTC, Luigi wrote:
> Hi everybody.
>
> I am tring to use a function where its parameter is another function, and at the same time are both already made - they cannot be modified - and the second one has to be conditioned before to be passed as argument.
>
> Let's say I have these function and I cannot modify:
>
> -jac(+d) that works on function and return real
>
> real jac(real function(real) fun, real x) {return d(fun, x);}
> real d(real function(real) fun, real x) {return fun(x);}
>
> -F1 that works on two reals and return real
>
> real F1(real a, real b) {return a + b;}
>
> So I need a way to condition F1 fixing b and then pass it to jac as argument.
>
> To do that I've created a delegate 'simp' conditionig F1:
>
> real delegate(real) simp(real function(real, real) f, real x) {
> 	real _simp(real z) {
> 		return f(z, x);
> 		}
> 	return &_simp;
> 	}
> (here 'simp' fixes b at x).
>
> My main is:
>
> void main() {
> 	real x_n = 1;
> 	real x_m = -1;
> 	real delegate(real) s_n = simp(&F1, x_n);
> 	//auto J = jac(s_n, x_m); //Error: function app.jac (real function(real) fun, real x) is not callable using argument types (real delegate(real), real)
> 	}
>
> the code fails because jac expect as argument a function but I found only a delegate to obtain a simplified function without any touch at already made functions jac, d and F1.
>
> There is a clean way to make it possible? I mean: without to touch (neither rewrite) jac, d and F1, obtain simplied F1 to pass to jac.
>
> Thaks in advance to anyone could help me.
> Luigi

A combination of std.functional.reverseArgs and std.functional.partial might help. It's unfortunately we don't have a version that can set an arbitrary argument, only the first one; It would be an easy improvement to make.

On Friday, 1 May 2015 at 03:34:53 UTC, Luigi wrote:
> Hi everybody.
>
> I am tring to use a function where its parameter is another function, and at the same time are both already made - they cannot be modified - and the second one has to be conditioned before to be passed as argument.
>
> Let's say I have these function and I cannot modify:
>
> -jac(+d) that works on function and return real
>
> real jac(real function(real) fun, real x) {return d(fun, x);}
> real d(real function(real) fun, real x) {return fun(x);}
>
> -F1 that works on two reals and return real
>
> real F1(real a, real b) {return a + b;}
>
> So I need a way to condition F1 fixing b and then pass it to jac as argument.
>
> To do that I've created a delegate 'simp' conditionig F1:
>
> real delegate(real) simp(real function(real, real) f, real x) {
> 	real _simp(real z) {
> 		return f(z, x);
> 		}
> 	return &_simp;
> 	}
> (here 'simp' fixes b at x).
>
> My main is:
>
> void main() {
> 	real x_n = 1;
> 	real x_m = -1;
> 	real delegate(real) s_n = simp(&F1, x_n);
> 	//auto J = jac(s_n, x_m); //Error: function app.jac (real function(real) fun, real x) is not callable using argument types (real delegate(real), real)
> 	}
>
> the code fails because jac expect as argument a function but I found only a delegate to obtain a simplified function without any touch at already made functions jac, d and F1.
>
> There is a clean way to make it possible? I mean: without to touch (neither rewrite) jac, d and F1, obtain simplied F1 to pass to jac.

If x_n is a constant (enum), you can use that to create a function instead of a delegate:

----
void main() {
    enum real x_n = 1;
    real x_m = -1;
    real function(real) s_n = z => F1(z, x_n);
    auto J = jac(s_n, x_m);
}
----

If x_n is not constant, then the only way I see to make this work, is to use a module variable:

----
real x_n;
void main() {
    x_n = 1;
    real x_m = -1;
    real function(real) s_n = z => F1(z, x_n);
    auto J = jac(s_n, x_m);
}
----

On Friday, 1 May 2015 at 11:03:19 UTC, anonymous wrote:
> If x_n is a constant (enum), you can use that to create a function instead of a delegate:
>
> ----
> void main() {
>     enum real x_n = 1;
>     real x_m = -1;
>     real function(real) s_n = z => F1(z, x_n);
>     auto J = jac(s_n, x_m);
> }
> ----
>
> If x_n is not constant, then the only way I see to make this work, is to use a module variable:
>
> ----
> real x_n;
> void main() {
>     x_n = 1;
>     real x_m = -1;
>     real function(real) s_n = z => F1(z, x_n);
>     auto J = jac(s_n, x_m);
> }
> ----

On Friday, 1 May 2015 at 06:48:46 UTC, John Colvin wrote:
> A combination of std.functional.reverseArgs and std.functional.partial might help. It's unfortunately we don't have a version that can set an arbitrary argument, only the first one; It would be an easy improvement to make.

Thank you both. I understood what you have shown to me.
About the chain 'reverseArg'+'partial' I reached to use it partially, only the partial part; so it worked with exception of reverseArg. I made several attempt to make it working but without succes.

About the scope/declaration suggestion they worked, fine. I've also made a change declaring x_s as static and worked as well (without change of scope and without use of enum).

Unfortunatly I tried to exted the code by introducing array of functions F1->[F1, F2, ...] and I saw such solution cannot apply. That why because of built functions passed (as example) to lambda function they do not store information. And I went back to delegates that store the necessary data to create the correct function. I've seen some method to pass from delegates to function, but onestly I found a to complex approach and much more a workaround that a good programming.
Going back to my study of D I will find the right way of thinking to approch such problems (I imagine now the trick could be using templates... I will see).

Thanks again. I've learned many things by looking at you solution.

ERRATA CORRIGE:
in place of x_s replace with x_n.
Sorry