weaselhat » Blog

@mgrnbrg on twitter

Michael Greenberg — Wed, 01 Feb 2012 16:07:58 +0000

Just a note: I’ve had a (mostly idle) Twitter account for a while, @mgrnbrg. Feel free to say hello!

Lovelace and Babbage vs. The Organist

Michael Greenberg — Wed, 19 Jan 2011 19:33:35 +0000

The latest and longest-yet episode of the graphic novel Lovelace and Babbage—Lovelace and Babbage vs. the Organist—at 2D Goggles has come to a close. If you haven’t seen it before, check it out! I highly recommend it.

Nested functions in GCC

Michael Greenberg — Wed, 03 Mar 2010 16:06:40 +0000

GCC supports “nested functions” using the -fnested-functions flag. When I first saw this, I was excited: closures in C! In the famous words of Admiral Ackbar, “it’s a trap!”

C [Show Styled Code]:

#include 

typedef int (*fptr)(int);

fptr f(int arg) {
  int nested_function(int nested_arg) {
    return arg + nested_arg;
  }

  return &nested_function;
}

void smash(int arg) {
  return;
}

int main(void) {
  fptr g = f(10);
  printf("%d\n", (*g)(5));
  smash(12);
  // printf("%d\n", (*g)(5));
  fptr h = f(12);
  printf("%d\n", (*g)(5));
  printf("%d\n", (*h)(5));

  return 0;
}

C [Show Plain Code]:

#include 
 
typedef int (*fptr)(int);
 
fptr f(int arg) {
  int nested_function(int nested_arg) {
    return arg + nested_arg;
  }
 
  return &nested_function;
}
 
void smash(int arg) {
  return;
}
 
int main(void) {
  fptr g = f(10);
  printf("%d\n", (*g)(5));
  smash(12);
  // printf("%d\n", (*g)(5));
  fptr h = f(12);
  printf("%d\n", (*g)(5));
  printf("%d\n", (*h)(5));
 
  return 0;
} 

Try compiling (gcc -fnested-functions). What does the second call to g produce—15 or 17? Try uncommenting line 21. What happens? Does commenting out line 20 affect this? What if line 19 is commented out, but lines 20 and 21 are uncommented?

I’m not sure this feature is worth it.

Type theory comes of age

Michael Greenberg — Fri, 12 Feb 2010 15:18:37 +0000

The current issue of the CACM has an article, Type theory comes of age. Not only is my advisor prominently depicted, but they also mention my area of research!

Thanks to Nate Foster for pointing this out to me.

Gravatar support

Michael Greenberg — Sun, 31 May 2009 18:40:14 +0000

I’ve added gravatar support to the website. The gravatar system is a clever way to create identity on-line: e-mails are associated with images. Critically, the URL associated with an e-mail doesn’t include the e-mail itself, but instead an MD5 hash — this way, spammers can’t harvest your address.

I was disappointed to discover that Google Chat doesn’t have support for gravatars — a Google labs feature I would use.

The University of Pennsylvania

Michael Greenberg — Mon, 16 Apr 2007 21:27:37 +0000

Last week I accepted the University of Pennsylvania‘s offer to study for a PhD (in PL). A few cool people there:

I’m really excited!

A New Term

Michael Greenberg — Mon, 22 Jan 2007 15:59:38 +0000

A new term starts on Wednesday, but the following are all on the list for discussion:

Dan Friedman, et al. The Reasoned Schemer
Flapjax: lifting and a few growing pains
My thesis

Weaselhat?

Michael Greenberg — Wed, 21 Jun 2006 16:07:57 +0000

Harking to Mark Liberman of Language Log‘s call for science blogs, I’ve started up this bit of silliness. I’m a computer science student, focusing on verification, temporal logic, and programming language theory. You know, the usual.

The name is random, left over from software I used to write. I have my own image, but try to free associate the two: weasel, hat; hat, weasel. Yes, yes, that’s good.