Should the type signature of def in Hints be SomeMonad SomeVariable -> Integer?

Oh sorry, I'm too naive(and yesterday I'm too tired to think about it).

The Greatest kata I have solved!

Until this moment I can't believe these things in programming (types, classes, and so on) have so much to do with mathematics.

Could someone tell me where (or how) to learn more about this?

Oh maybe I know how to do that. Thank you! :)

I know, but I don't know how to apply arguments to the block { having(5).fingers }. I can't understand why the block { having(5).fingers } accepts no arguments (instead of { |x| having(5).fingers.call(x) }).

Is the C++ test wrong?

It always exited prematurely with a SIGSEGV signal.

When I run the sample test code on my computer, it seems that in the code(Sample Test, Line29)

for (int i = 0; i < 4; ++i) if (memcmp (puzzle[i], expected[i], 4*sizeof (int))) return 0;

I create int ans[4][4] and return it, gdb tells me that in equal, puzzle is (int **) 0x5555557913a0 <ans> but *puzzle is 0x300000001, **puzzle is Cannot access memory.

It seems that something goes wrong with int**. Shouldn't it be (int(*)[4])? Or how can I create a array to make it?