PAKCS
Exported names: Imported modules:

Module System.Random

Library for pseudo-random number generation in Curry.

This library provides operations for generating pseudo-random number sequences. For any given seed, the sequences generated by the operations in this module should be identical to the sequences generated by the java.util.Random package.

The KiCS2 implementation is based on an algorithm taken from http://en.wikipedia.org/wiki/Random_number_generation. There is an assumption that all operations are implicitly executed mod 2^32 (unsigned 32-bit integers) !!! GHC computes between -2^29 and 2^29-1, thus the sequence is NOT as random as one would like. 

m_w = <choose-initializer>;    /* must not be zero */
m_z = <choose-initializer>;    /* must not be zero */
uint get_random()
{
    m_z = 36969 * (m_z & 65535) + (m_z >> 16);
    m_w = 18000 * (m_w & 65535) + (m_w >> 16);
    return (m_z << 16) + m_w;  /* 32-bit result */
}

The PAKCS implementation is a linear congruential pseudo-random number generator described in Donald E. Knuth, The Art of Computer Programming, Volume 2: Seminumerical Algorithms, section 3.2.1.

Author: Sergio Antoy (with extensions by Michael Hanus)

Version: June 2017

Summary of exported operations:

nextInt :: Int -> [Int]   
Returns a sequence of pseudorandom, integer values.
nextIntRange :: Int -> Int -> [Int]   
Returns a pseudorandom sequence of values between 0 (inclusive) and the specified value (exclusive).
nextBoolean :: Int -> [Bool]   
Returns a pseudorandom sequence of boolean values.
getRandomSeed :: IO Int   
Returns a time-dependent integer number as a seed for really random numbers.
shuffle :: Int -> [a] -> [a]   
Computes a random permutation of the given list.

Exported operations:

nextInt :: Int -> [Int]   

Returns a sequence of pseudorandom, integer values.

Example call:
(nextInt seed)
Parameters:
  • seed : The seed of the random sequence.

nextIntRange :: Int -> Int -> [Int]   

Returns a pseudorandom sequence of values between 0 (inclusive) and the specified value (exclusive).

Example call:
(nextIntRange seed n)
Parameters:
  • seed : The seed of the random sequence.
  • n : The bound on the random number to be returned. Must be positive.

nextBoolean :: Int -> [Bool]   

Returns a pseudorandom sequence of boolean values.

Example call:
(nextBoolean seed)
Parameters:
  • seed : The seed of the random sequence.

getRandomSeed :: IO Int   

Returns a time-dependent integer number as a seed for really random numbers. Should only be used as a seed for pseudorandom number sequence and not as a random number since the precision is limited to milliseconds

shuffle :: Int -> [a] -> [a]   

Computes a random permutation of the given list.

Example call:
(shuffle rnd l)
Parameters:
  • rnd : random seed
  • l : lists to shuffle
Returns:
shuffled list