Category: lisp

SBCL 1.0.55 x64 needs GLIBC 2.14

It installed on my Ubuntu 11.10 (Oneiric) laptop, but when I tried to run it, I got this message:

sbcl: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.14' not found (required by sbcl)

Hmmm. Let’s see..

# ls -al /lib/x86_64-linux-gnu/libc.so.6
lrwxrwxrwx 1 root root 12 2012-03-06 21:17 /lib/x86_64-linux-gnu/libc.so.6 -> libc-2.13.so

Argh.

This has already been reported in the SBCL bug database.

My workaround was to grab 1.0.54 from the old file releases section on SBCL’s sourceforge site. That worked fine. So you’ll need to downgrade if you want to use the 64 bit version.

This came up when I ran into problems installing cl-libxml2 using quicklisp. The x86 version of SBCL throws an error when using cffi to load the Ubuntu-packaged libxml2 library, because it expects a 32-bit version of the library but finds a 64-bit one instead (I neglected to copy the error message, but it’s something about finding an unexpected/wrong class ELFCLASS64).

So I suspect anyone who has a x64 system that uses cffi to access libraries in this manner will run into the same problem with SBCL 1.0.55.

On a side note, I can’t imagine installing and managing Common Lisp libraries without quicklisp. It took a few seconds to do what would probably take a beginner like me hours to figure out. Awesome tools like that make a huge difference to newcomers who want to get up and running with CL without a lot of pain.

* * *

UPDATE: This is fixed in 1.0.56.

A Good Video Discussion on Clojure

The other day, I discovered this wonderful video from 2009. It’s an informal chat/whiteboard session with Rich Hickey, the creator of Clojure, on Microsoft’s Channel 9.

Watching it really helped solidify in my brain various concepts around Lisp and Clojure that I’ve been trying to learn recently in my spare time. I didn’t grasp every tangential reference to various debates in the world of languages and compilers (and there are many of them in this video!) but it’s still worth watching for the interested layperson who’s trying to delve into the world of functional programming.

The best part, for me, is Rich’s explanation of how data structures in Clojure are immutable yet very fast when it comes to copying. This seems counterintuitive, since, on the face of it, you would think that it’s very slow to have to copy whole data structures to make changes. The secret is that it doesn’t do a deep copy. The underlying implementation of lists and sequences uses shallow trees: “copies” of data only need to clone a short branch of the tree and reference a new root node, which also keeps the old data structure intact. The discussion is wonderfully elegant.

Having used only imperative languages my entire life, this recent foray into Lisps and functional programming has been really challenging and eye-opening. Putting aside its alleged strengths and advantages, I find the mathematical flavor of this style of coding very appealing. I don’t have a mathematically-oriented brain, but at the same time, oddly enough, something about Lisps seems truer to what I intuit the essence of computing to be. If I were formally trained in computational theory, I’m sure I’d have some fancy jargon to name this quality I’m trying to describe. As it stands, I can only say it feels close to the machine.

Making Emacs an IDE

It’s that time when bloggers wax introspective about the past year. For me, the major personal revelation in 2011 was re-discovering something very old, and putting it to new use. For me, 2011 was the year of the Emacs IDE.

I’ve been using Emacs, on and off, for close to a decade now. What’s changed is that, in the past few months, I’ve been writing extensions for it. It started with a simple desire to better navigate files in a complex directory hierarchy that followed specific and somewhat convoluted conventions. At first, learning Emacs Lisp was simply a means to an end, but I ended up liking it so much that I started exploring Common Lisp (and more recently, Clojure, since I’ve worked with Java in the past).

What started as a small task has become a larger project of turning Emacs into an IDE.

To understand this, one needs to know some context about the system I work with. We developers edit tons of XML files and files in other text formats, which all drive our proprietary web application product. We have many command line tools that manipulate these files in various ways; the system was originally designed by folks who followed the UNIX philosophy of building orthogonal tools and chaining them together.

There are pros and cons to this system; for reasons I won’t get into, I don’t love it, but it’s what we work with right now. When I started the job, the vast majority of the developers used screen, vi, and the shell prompt. Typical workflows that involved working with only a few files could be extremely hard to keep track of, and usually required a lot of copying and pasting between screen and/or ssh sessions. Few people seemed to mind, but I found the workflow to contain too much extraneous cognitive load, and the state of the tools made development very prone to error.

Gradually, I’ve been integrating our tools into Emacs. Sometimes that simply means binding a key combination to running a diagnostics program and storing the output in a buffer. Sometimes it means accumulating that output for history’s sake. Sometimes it means parsing program output, processing it in Emacs Lisp, and inserting a result into the current buffer. Sometimes it means running external programs, even GUI applications, and tweaking them a bit to tell Emacs to open specific files you want to look at.

The productivity gains have been amazing. This is no reason to brag: managing several screen sessions with different vi and shell instances wasn’t exactly hard to improve upon. But Emacs made it fairly painless. Emacs Lisp has proved to be wonderful “glue” for integrating existing tools in our environment.

Writing tools that enable you to do other job tasks better is a really interesting experience; I’ve never done it to such an extensive degree. So far, one other person in my group is using this Emacs IDE, and she has been happy with how much it facilitates her work. Others who swing by my desk for something often watch me work for a moment, and ask, “how did you do that?! that’s not vi, is it?”

Getting more people to switch over means convincing them that the steep learning curve of Emacs is worth the gains of the integration I’ve done. I’m not sure how much that will happen, since a big part of it is cultural. But if there aren’t any more converts, I don’t really care. The best thing about this ongoing project is that I am the end user. The software I wrote is really for myself. It is something I use intensively every single day. And that makes it all the more gratifying.

Getting the Solarized Theme to Work in Emacs

I discovered the Solarized color palette about a month ago, and have been using it since. I’ve found it helpful for reducing eye strain.

Getting the palette colors to accurately display in terminal-based Emacs under Ubuntu 11.10 took a bit of work. There’s a lot of scattered info about this topic if you google around. I first tried to do it with as little modification to my system as possible (I’m a minimalist), but I found that I absolutely had to do these three things to get it working.

1) Set the color palette in gnome-terminal. No matter what I tried, I could not get Emacs colors to look right without this step, so it’s a crucial one. Don’t skip it.

Solarized comes with an Xdefaults file, but that didn’t work for me. This blog post had instructions for setting gnome-terminal colors using gconftool-2, and that worked very nicely.

I put the commands in a handy little shell script that allows you to choose either the light or dark version of the palette. You can get it here:

https://gist.github.com/1397104

2) Your TERM environment variable needs to be set to “xterm-256color.” The default “xterm” will cause the Solarized color theme to look completely crazy in emacs.

Add the following line to your ~/.bashrc line (if you already set TERM there or some elsewhere else, change it instead of adding this):

export TERM="xterm-256color"

3) Use this version of the Emacs color theme for Solarized:

https://github.com/sellout/emacs-color-theme-solarized

Note that unless you’re using Emacs 24 (pre-release source code tarballs are available here), you’ll also need the color-theme package if you don’t already have it installed.

Put the files in a directory. In your .emacs file, you’ll need to add the directory to your load-path; I also added a bit of conditional logic for how to load the color theme in Emacs 23 and 24, since I switch between them:

(add-to-list 'load-path "~/.emacs.d/emacs-color-theme-solarized")
(if
    (equal 0 (string-match "^24" emacs-version))
    ;; it's emacs24, so use built-in theme 
    (require 'solarized-dark-theme)
  ;; it's NOT emacs24, so use color-theme
  (progn
    (require 'color-theme)
    (color-theme-initialize)
    (require 'color-theme-solarized)
    (color-theme-solarized-dark)))

That should do it.

Learning Lisp

For work projects, I often have to jump around a lot of XML files referenced in one another by name. The files follow a strict naming convention, but it’s one that looks like gibberish to human eyes. Typing them is difficult and prone to error; plus there are so many files in a given project that navigating a visual tree of the directory isn’t much easier.

So I wrote a small library for Emacs to find and open a file in the directory tree, if the cursor is over a string of text that matches a valid filename in the convention. I’m embarrassed to admit this took me two full days (a few other functions were in the library too). The only previous exposure to Emacs Lisp I had was tweaking my .emacs file, so I had to learn the language as well as hunt down the right functions to call for what I wanted. The work is paying off: it feels 10x’s easier to navigate project files now.

I experimented with trying to do this in Komodo Edit, a popular editor among coworkers, but it involved learning Mozilla’s XUL and Komodo’s own API, as well as writing javascript (yuck), so I abandoned that effort pretty quickly.

I didn’t think I would like Lisp, but the experience has been pretty fascinating, and I’m now making my way through the Practical Common Lisp book by Peter Seibel. It’s interesting learning a language that’s half a century old (!), and that’s influenced so many contemporary languages. One might think that there’s nothing there worth learning or revisiting, but that is so wrong. In particular, I’m trying to wrap my head around the power of Lisp macros and the way they allow you to create new syntactic abstractions. The idea of extending the very language itself, rather just adding new functions, is mind-boggling, to say the least. And, from what I understand, it remains fairly unique to Lisp in spite of the flood of new languages in the past few decades.

It’s disheartening not being able to find much info about who actually uses Lisp anymore, aside from hackers building modules for Emacs. Paul Graham has a cool essay, “Beating the Averages”, about using Lisp to build online store software that Yahoo eventually acquired. And ITA software, which makes an airfare search engine that powers the entire travel industry, uses Lisp. But aside from these bits of info, there isn’t much out there in the way of Lisp “success stories.”