Function Currying

[Hasan Aljudy]

Is everyone supposed to know what currying means? and what are its uses?

Walter Bright wrote:
> D's tuple support has reached the point where function currying is 
> straightforward. I held off from doing a standard library with these 
> because Tom S's bind library is much more comprehensive, and I hope 
> he'll update it with these.
> 
> ------ Curry first argument -----------------
> 
> R delegate(U) Curry(Dummy=void, R, A, U...)(R function(A, U) dg, A arg)
> {
>     struct Foo
>     {
>     typeof(dg) dg_m;
>     typeof(arg) arg_m;
> 
>     R bar(U r)
>     {
>         return dg_m(arg_m, r);
>     }
>     }
> 
>     Foo* f = new Foo;
>     f.dg_m = dg;
>     f.arg_m = arg;
>     return &f.bar;
> }
> 
> R delegate(U) Curry(R, A, U...)(R delegate(A, U) dg, A arg)
> {
>     struct Foo
>     {
>     typeof(dg) dg_m;
>     typeof(arg) arg_m;
> 
>     R bar(U r)
>     {
>         return dg_m(arg_m, r);
>     }
>     }
> 
>     Foo* f = new Foo;
>     f.dg_m = dg;
>     f.arg_m = arg;
>     return &f.bar;
> }
> 
> void main()
> {
>     static int plus(int x, int y, int z)
>     {
>     return x + y + z;
>     }
> 
>     auto plus_two = Curry(&plus, 2);
>     printf("%d\n", plus_two(6, 8));
>     auto plus_three = Curry(plus_two, 3);
>     printf("%d\n", plus_three(7));
> 
>     int minus(int x, int y, int z)
>     {
>     return x + y + z;
>     }
> 
>     auto minus_two = Curry(&minus, 2);
>     printf("%d\n", minus_two(6, 8));
>     auto minus_three = Curry(minus_two, 3);
>     printf("%d\n", minus_three(7));
> }
> -------- Curry all the arguments -------------------------
> 
> R delegate() CurryAll(Dummy=void, R, U...)(R function(U) dg, U args)
> {
>     struct Foo
>     {
>     typeof(dg) dg_m;
>     U args_m;
> 
>     R bar()
>     {
>         return dg_m(args_m);
>     }
>     }
> 
>     Foo* f = new Foo;
>     f.dg_m = dg;
>     foreach (i, arg; args)
>     f.args_m[i] = arg;
>     return &f.bar;
> }
> 
> R delegate() CurryAll(R, U...)(R delegate(U) dg, U args)
> {
>     struct Foo
>     {
>     typeof(dg) dg_m;
>     U args_m;
> 
>     R bar()
>     {
>         return dg_m(args_m);
>     }
>     }
> 
>     Foo* f = new Foo;
>     f.dg_m = dg;
>     foreach (i, arg; args)
>     f.args_m[i] = arg;
>     return &f.bar;
> }
> 
> 
> void main()
> {
>     static int plus(int x, int y, int z)
>     {
>     return x + y + z;
>     }
> 
>     auto plus_two = CurryAll(&plus, 2, 3, 4);
>     printf("%d\n", plus_two());
>     assert(plus_two() == 9);
> 
>     int minus(int x, int y, int z)
>     {
>     return x + y + z;
>     }
> 
>     auto minus_two = CurryAll(&minus, 7, 8, 9);
>     printf("%d\n", minus_two());
>     assert(minus_two() == 24);
> }
> -----------------------