alphomega - Developer IT

Applying a function to an arbitrarily long list of arguments

- by alphomega

I want to create a function apply that takes a function with an arbitrary amount of arguments as well as a list of integers, and returns the result of the function (Where each integer in the list is an argument in order. I was thinking something like: apply :: ([Int] -> Int) -> [Int] -> Int apply f x:xs = apply (f x) xs apply f [] = f But I know this won't work because the type signature is wrong - the function doesn't take a list of ints, it just takes some amount of int arguments. Additionally, when I get to the base case the f argument to apply should actually be an integer, violating the type signature anyway. Does anyone know how to deal with this sort of problem?

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Reading in 4 bytes at a time

- by alphomega

I have a big file full of integers that I'm loading in. I've just started using C++, and I'm trying out the filestream stuff. From everything I've read, it appears I can only read in bytes, So I've had to set up a char array, and then cast it as a int pointer. Is there a way I can read in 4 bytes at a time, and eliminate the need for the char array? const int HRSIZE = 129951336; //The size of the table char bhr[HRSIZE]; //The table int *dwhr; int main() { ifstream fstr; /* load the handranks.dat file */ std::cout << "Loading table.dat...\n"; fstr.open("table.dat"); fstr.read(bhr, HRSIZE); fstr.close(); dwhr = (int *) bhr; }

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Program to find the result of primitive recursive functions

- by alphomega

I'm writing a program to solve the result of primitive recursive functions: 1 --Basic functions------------------------------ 2 3 --Zero function 4 z :: Int -> Int 5 z = \_ -> 0 6 7 --Successor function 8 s :: Int -> Int 9 s = \x -> (x + 1) 10 11 --Identity/Projection function generator 12 idnm :: Int -> Int -> ([Int] -> Int) 13 idnm n m = \(x:xs) -> ((x:xs) !! (m-1)) 14 15 --Constructors-------------------------------- 16 17 --Composition constructor 18 cn :: ([Int] -> Int) -> [([Int] -> Int)] -> ([Int] -> Int) 19 cn f [] = \(x:xs) -> f 20 cn f (g:gs) = \(x:xs) -> (cn (f (g (x:xs))) gs) these functions and constructors are defined here: http://en.wikipedia.org/wiki/Primitive_recursive_function The issue is with my attempt to create the compositon constructor, cn. When it gets to the base case, f is no longer a partial application, but a result of the function. Yet the function expects a function as the first argument. How can I deal with this problem? Thanks.

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Pattern matching for lambda expressions

- by alphomega

21 --Primitive recursion constructor 22 pr :: ([Int] -> Int) -> ([Int] -> Int) -> ([Int] -> Int) 23 pr f g = \xs 0 -> f xs 24 pr f g = \xs (y+1) -> g xs y ((pr f g) xs y) I want the function this function creates to act differently on different inputs, so that it can create a recursive function. As expected, the above code doesn't work. How do I do something like pattern matching, but for the function it creates? Thanks

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Finding the size of a pointer

- by alphomega

printf("pointer: %d\n", sizeof(*void)); This line results in a syntax error because of the *. What should I do to get it to work?

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