## digitalmars.D.learn - How to reuse functions

- Luigi (38/38) Apr 30 2015 Hi everybody.
- John Colvin (5/43) Apr 30 2015 A combination of std.functional.reverseArgs and
- anonymous (22/58) May 01 2015 If x_n is a constant (enum), you can use that to create a

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

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. LuigiA 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

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

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

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

May 01 2015