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digitalmars.D.learn - How to reuse functions

reply "Luigi" <mimasci gmail.com> writes:
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
Apr 30 2015
next sibling parent "John Colvin" <john.loughran.colvin gmail.com> writes:
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.
Apr 30 2015
prev sibling parent reply "anonymous" <anonymous example.com> writes:
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);
}
----
May 01 2015
parent reply "Luigi" <mimasci gmail.com> writes:
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.
May 01 2015
parent "Luigi" <mimasci gmail.com> writes:
ERRATA CORRIGE:
in place of x_s replace with x_n.
Sorry
May 01 2015