teaching machines

CS 330 Lecture 24 – Promises, Tail Recursion, and Currying

April 3, 2013 by Chris Johnson. Filed under
Deprecated: Creation of dynamic property WP_Term::$cat_ID is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 378

Deprecated: Creation of dynamic property WP_Term::$category_count is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 379

Deprecated: Creation of dynamic property WP_Term::$category_description is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 380

Deprecated: Creation of dynamic property WP_Term::$cat_name is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 381

Deprecated: Creation of dynamic property WP_Term::$category_nicename is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 382

Deprecated: Creation of dynamic property WP_Term::$category_parent is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 383

Deprecated: Creation of dynamic property WP_Term::$cat_ID is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 378

Deprecated: Creation of dynamic property WP_Term::$category_count is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 379

Deprecated: Creation of dynamic property WP_Term::$category_description is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 380

Deprecated: Creation of dynamic property WP_Term::$cat_name is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 381

Deprecated: Creation of dynamic property WP_Term::$category_nicename is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 382

Deprecated: Creation of dynamic property WP_Term::$category_parent is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 383

Deprecated: Creation of dynamic property WP_Term::$cat_ID is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 378

Deprecated: Creation of dynamic property WP_Term::$category_count is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 379

Deprecated: Creation of dynamic property WP_Term::$category_description is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 380

Deprecated: Creation of dynamic property WP_Term::$cat_name is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 381

Deprecated: Creation of dynamic property WP_Term::$category_nicename is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 382

Deprecated: Creation of dynamic property WP_Term::$category_parent is deprecated in /var/www/twodee/blog/wp-includes/category.php on line 383
cs330, lectures, spring 2013.

Agenda

• what ?s
• delaying evaluation
• tail recursion
• partially applying functions

TODO

• Read http://learnyouahaskell.com/higher-order-functions again. No quarter sheet.

Code

macro.c

#include <stdio.h>
#include <stdlib.h>

#define PRINTN(n, expr) \
  for (int i = 0; i < n; ++i) { \
    printf("%d", expr); \
  } \
  printf("\n");

int getZero() {
  printf("1");
  return 0;
}

int main(int argc, char **argv) {
  PRINTN(5, getZero());
  return 0;
}

promise.html

<!DOCTYPE html>
<html>
<head>
  <title>...</title>
</head>
<body>
  
<script>
function Promise(thunk) {
  this.thunk = thunk;
  this.isResolved = false;
  this.val = null;
}

Promise.prototype.resolve = function() {
  if (!this.isResolved) {
    this.val = this.thunk();
    this.isResolved = true;
  }
  return this.val;
}

promise = new Promise(function() {alert('hello, world'); return 'A'});
document.write(promise.resolve());
document.write(promise.resolve());
document.write(promise.resolve());
document.write(promise.resolve());
document.write(promise.resolve());
document.write(promise.resolve());
document.write(promise.resolve());
document.write(promise.resolve());
document.write(promise.resolve());
document.write(promise.resolve());
document.write(promise.resolve());
document.write(promise.resolve());
document.write(promise.resolve());
document.write(promise.resolve());
document.write(promise.resolve());
</script>

</body>
</html>

sum.hs

sumAccum [] accum = accum
sumAccum (first:rest) accum = sumAccum rest (accum + first)

sum' list = sumAccum list 0

clamp lo hi n
  | n < lo = lo
  | n > hi = hi
  | otherwise = n

clampPercent = clamp 0 100

Haiku