teaching machines

CS 330 Lecture 37 – Sundries

May 4, 2012 by Chris Johnson. Filed under cs330, lectures, spring 2012.

Agenda

• more on hijacking a language
• applicative- vs. normal-order evaluation
• writing an if macro
• macros in C
• dangers of normal-order evaluation of expressions with side-effects
• list ranges
• list comprehensions
• lazy evaluation

TODO

• http://www.cse.chalmers.se/~rjmh/Papers/whyfp.pdf
• http://www.haskell.org/haskellwiki/Why_Haskell_matters

Code

macros.ss

(define myif
  (lambda (predicate? true-expr false-expr)
    (cond
      (predicate? 1)
      (else 0))))

(define-syntax spiffy
  (syntax-rules ()
    ((spiffy predicate? true-expr false-expr)
     (cond
       (predicate? true-expr)
       (else false-expr)))))

numbers.cpp

#include <iostream>

#define MAX(a, b) (a > b ? a : b)

int ReadInt() {
  int i;
  std::cin >> i;
  return i;
}

int main() {
  /* std::cout << "MAX(5, 7): " << MAX(5, 7) << std::endl; */
  std::cout << "MAX(#, #): " << MAX(ReadInt(), ReadInt()) << std::endl;
  return 0;
}

haskfun.hs

nsum 0 = 0
nsum n = n + nsum (n - 1)

plus a b = a + b

Haiku