I made a number of Google searches of the forms below and summed the results (previous posts averaged the results):

"implemented in <language>"
  "written in <language>"

Naturally this is of very limited utility, and the numbers are only useful when comparing relatively within the same search since the number of results Google returns can vary greatly over time.

¹ combines Lisp, Scheme, Common Lisp, Arc & Clojure
² combines OCaml, (S)ML, Caml
³ summed separate searches for sml and ml

The following Haskell solution seems very readable to me, but it’s a naive solution that’s inefficient. It computes an answer on my 2.6 year old Macbook Pro in under 4 seconds, but a 2x increase in text requires a 7x increase in CPU time.

I believe there are algorithms to find the longest embedded palindrome in linear time, so I may post a refinement later.

-- Find the longest palindrome in a text string.

module Main where
import Char

text = "I'll just type in some example text here and embed a little \
\palindrome - A man, a plan, a canal, Panama! - I expect that will be \
\the longest palindrome found in this text.\
\Lorem ipsum dolor sit amet, consectetur adipiscing elit.\
\Integer volutpat lorem imperdiet ante bibendum ullamcorper. Mauris \
\tempor hendrerit justo at elementum. Vivamus elit magna, accumsan id \
\condimentum a, luctus a ipsum. Donec fermentum, lectus at posuere \
\ullamcorper, mauris lectus tincidunt nulla, ut placerat justo odio sed\
\ odio. Nulla blandit lorem sit amet odio varius nec vestibulum ante \
\ornare. Aliquam feugiat, velit a rhoncus rutrum, turpis metus pretium \
\dolor, et mattis leo turpis non est. Sed aliquet, sapien quis \
\consequat condimentum, sem magna ornare ligula, id blandit odio nisl \
\vitae erat. Nam vulputate tincidunt quam, non lacinia risus tincidunt \
\lacinia. Aenean fermentum tristique porttitor. Nam id dolor a eros \
\accumsan imperdiet. Aliquam quis nibh et dui ultricies cursus. Nunc \
\et ante non sapien vehicula rutrum. Duis posuere dictum blandit. Nunc \
\vitae tempus purus."

clean = map toLower . filter isAlpha

palindrome str = str == reverse str

substrings []     = []
substrings (x:xs) = substrings' (x:xs) ++ substrings xs where
  substrings' []     = []
  substrings' (y:ys) = [y] : [ (y:s) | s <- substrings' ys ]

longest []     = []
longest (x:xs) = if length x > length max then x else max
  where max = longest xs

longest_palindrome xs =
  longest (filter palindrome (substrings (clean text)))

main = print (longest_palindrome text)

As a comparison, I translated the program into Ruby. I program predominantly in Ruby these days, and I like it, but the Ruby version is 25 times slower (98 sec. vs. 4 sec.), and it’s 2.4 times more lines of code (31 vs. 13 – excluding the text).

A gain in runtime efficiency, expressive power and multi-core capability is very attractive!

I’m using Ruby 1.9.2 and GHC 6.12.3 on Mac OS X 10.5.8 on a 2.4 GHz Core 2 Duo w/ 4 GB RAM.

ruby 1.9.2p0 (2010-08-18 revision 29036) [i386-darwin9.8.0]
Glasgow Haskell Compiler, Version 6.12.3, for Haskell 98, stage 2 booted by GHC version 6.12.2

TEXT = <<END
I'll just type in some example text here and embed a little
palindrome - A man, a plan, a canal, Panama! - I expect that will be
the longest palindrome found in this text.
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Integer volutpat lorem imperdiet ante bibendum ullamcorper. Mauris
tempor hendrerit justo at elementum. Vivamus elit magna, accumsan id
condimentum a, luctus a ipsum. Donec fermentum, lectus at posuere
ullamcorper, mauris lectus tincidunt nulla, ut placerat justo odio sed
 odio. Nulla blandit lorem sit amet odio varius nec vestibulum ante
ornare. Aliquam feugiat, velit a rhoncus rutrum, turpis metus pretium
dolor, et mattis leo turpis non est. Sed aliquet, sapien quis
consequat condimentum, sem magna ornare ligula, id blandit odio nisl
vitae erat. Nam vulputate tincidunt quam, non lacinia risus tincidunt
lacinia. Aenean fermentum tristique porttitor. Nam id dolor a eros
accumsan imperdiet. Aliquam quis nibh et dui ultricies cursus. Nunc
et ante non sapien vehicula rutrum. Duis posuere dictum blandit. Nunc
vitae tempus purus.
END

def clean str
  str.gsub(/[^A-Za-z]/,'').downcase
end

def palindrome? str
  str == str.reverse
end

def subs str
  return [] if str.empty?
  y = str[0,1]
  subs(str[1..-1]).inject([y]) do |result, s|
    result << y + s
    result
  end
end

def substrings str
  return [] if str.empty?
  subs(str) + substrings(str[1..-1])
end

def longest strs
  strs.inject("") do |max, str|
    max = str if str.length > max.length
    max
  end
end

def longest_palindrome str
  longest(substrings(clean(str)).inject([]) {|result, str|
            result << str if palindrome?(str)
            result
          })
end

puts longest_palindrome(TEXT)

Update 3/13/11 19:30
Rick’s comment (see his blog post linked to in his comment) regarding the importance of algorithm choice is certainly a valid one – a better algorithm in a slower language may win over an inferior algorithm in a faster language (for large enough datasets). However, what I’m becoming interested in is the fact that one may gain both productivity/power and runtime speed by making wise programming language choices.

In the case of an interpreted language such as Ruby, it’s helpful to “stay in C code” as much as possible. In other words, to favor built-in library routines that have been implemented in C over hand written Ruby code. As much as I like Ruby, this is one of the things that bothers me – the fact that the Ruby code written by the programmer is vastly inferior in performance to the built-in library routines.

I wasn’t planning on refining the Haskell version this soon, but after seeing Rick’s blog post response, I couldn’t resist :)

I should first provide some background info for context. When I wrote the original Haskell version above, I was in the middle of an online programming challenge, and my goal was simply to compute the answer in a reasonable amount of time to move on to the next challenge, so the brief, easily understandable, Haskell version worked great. Hence, my disclaimers in the post regarding the naivity and inefficiency of the solution. The Ruby code in this post was an afterthought simply to see a comparison between identical algorithms. Given that apple & apple comparison, I’m impressed with the brevity and speed of the Haskell version.

Since I’m still very much a Haskell newbie, and short on time, I found an incredible solution by Johan Jeuring. It’s a little bit longer than the Ruby version, but much, much faster. It’s so fast, I had to increase the input quite a bit to get a reasonable comparison – I replicated the original text 23 times and reversed one of the replications to make a fairly long palindrome.

Rick’s Ruby version took 169.4 seconds, Johan’s Haskell version took 0.032 seconds. In other words, Ruby takes over 5,000 times as long to compute the result. Clearly this is an apples and oranges comparison, but I fully expect that a Ruby version using an identical algorithm will take 100 times as long (or longer) to run and would be less concise. Giving up runtime performance to gain programmer power is one thing, but giving up runtime performance and power is a tough pill to swallow.

Here is a slightly modified version of Johan Jeuring’s code. He was also kind enough to provide his code here:

-- Reorganized from Johan Jeuring's solution:
module Main where
import Data.List (maximumBy,intersperse)
import Data.Char
import Data.Array 

text = "I'll just type in some example text here and embed a little \
\palindrome - A man, a plan, a canal, Panama! - I expect that will be \
\the longest palindrome found in this text.\
\Lorem ipsum dolor sit amet, consectetur adipiscing elit.\
\Integer volutpat lorem imperdiet ante bibendum ullamcorper. Mauris \
\tempor hendrerit justo at elementum. Vivamus elit magna, accumsan id \
\condimentum a, luctus a ipsum. Donec fermentum, lectus at posuere \
\ullamcorper, mauris lectus tincidunt nulla, ut placerat justo odio sed\
\ odio. Nulla blandit lorem sit amet odio varius nec vestibulum ante \
\ornare. Aliquam feugiat, velit a rhoncus rutrum, turpis metus pretium \
\dolor, et mattis leo turpis non est. Sed aliquet, sapien quis \
\consequat condimentum, sem magna ornare ligula, id blandit odio nisl \
\vitae erat. Nam vulputate tincidunt quam, non lacinia risus tincidunt \
\lacinia. Aenean fermentum tristique porttitor. Nam id dolor a eros \
\accumsan imperdiet. Aliquam quis nibh et dui ultricies cursus. Nunc \
\et ante non sapien vehicula rutrum. Duis posuere dictum blandit. Nunc \
\vitae tempus purus."

clean = map toLower . filter isAlpha

longestPalindrome input =
  let inputArray      =  listArrayl0 input
      (maxLength,pos) =  maximumBy
                            (\(l,_) (l',_) -> compare l l')
                            (zip (palindromesAroundCentres inputArray) [0..])
  in showPalindrome inputArray (maxLength,pos)

longestPalindromes m input =
  let inputArray =  listArrayl0 input
  in concat $ intersperse "\n"
            $ map (showPalindrome inputArray)
            $ filter ((m<=) . fst)
            $ zip (palindromesAroundCentres inputArray) [0..]

lengthLongestPalindrome :: String -> String
lengthLongestPalindrome = show . maximum . palindromesAroundCentres . listArrayl0

lengthLongestPalindromes :: String -> String
lengthLongestPalindromes = show . palindromesAroundCentres . listArrayl0

palindromesAroundCentres a =
  let (afirst,_) = bounds a
  in reverse $ extendTail a afirst 0 []

extendTail a n currentTail centres
  | n > alast = finalCentres currentTail centres
                   (currentTail:centres)
  | n-currentTail == afirst =
      extendCentres a n (currentTail:centres)
                    centres currentTail
  | a!n == a!(n-currentTail-1) =
      extendTail a (n+1) (currentTail+2) centres
  | otherwise =
      extendCentres a n (currentTail:centres)
                    centres currentTail
  where  (afirst,alast)  =  bounds a

extendCentres a n centres tcentres centreDistance
  | centreDistance == 0 =
      extendTail a (n+1) 1 centres
  | centreDistance-1 == head tcentres  =
      extendTail a n (head tcentres) centres
  | otherwise =
      extendCentres a n (min (head tcentres)
                    (centreDistance-1):centres)
                    (tail tcentres) (centreDistance-1)

finalCentres 0     _        centres  =  centres
finalCentres (n+1) tcentres centres  =
  finalCentres n
               (tail tcentres)
               (min (head tcentres) n:centres)
finalCentres _     _        _        =  error "finalCentres: input < 0"               

showPalindrome a (len,pos) =
  let startpos = pos `div` 2 - len `div` 2
      endpos   = if odd len
                 then pos `div` 2 + len `div` 2
                 else pos `div` 2 + len `div` 2 - 1
  in show [a!n|n <- [startpos .. endpos]]

listArrayl0 string  = listArray (0,length string - 1) string

sampleText s = concat (replicate 8 s ++ [ "x" ] ++ [ reverse s ] ++ replicate 14 s)

main = print (longestPalindrome (clean (sampleText text)))

Here's the relevant change to Rick's Ruby version:

def sample_text str
  str * 8 + 'x' + str.reverse + str * 14
end

puts clean(sample_text(TEXT)).longest_palindrome

I’m still trying to get my head around Haskell, so I expect there are many possible improvements to this program, but even so, I’m pleased with how Haskell allows me to express logic.

-- Solve the Cracker Barrel Peg Board Puzzle

module Main where

type Pos = (Int, Int)
type Move = (Pos, Pos)
type Board = [ Pos ]

isOccupied b p = elem p b
isEmpty b p    = not (isOccupied b p)
isPos (r,c)    = elem r [0..4] && elem c [0..r]

-- Possible moves for one position
positionMoves b p = [ (p, dst) | (neighbor, dst) <- pairs,
                      isOccupied b neighbor &&
                      isEmpty b dst ]
  where (r, c) = p
        pairs  = filter (\(p1,p2) -> isPos p1 && isPos p2)
                   [ ((r + or `div` 2, c + oc `div` 2),(r + or, c + oc)) |
                     (or, oc) <- [ (-2,0), (0,2), (2,2), (2,0), (0,-2), (-2,-2) ] ]

-- Possible moves for all positions on the board
possibleMoves b = concat [ positionMoves b pos | pos <- b ]

-- Make a move and return the new board
move b (src,dst) = dst:filter pred b
  where ((sr,sc),(dr,dc)) = (src,dst)
        neighbor = (div (sr+dr) 2, div (sc+dc) 2)
        pred     = \pos -> (pos /= src) && (pos /= neighbor)

-- Make moves until the goal position is met
play b p moves =
  if null nextMoves then
    if length b == 1 && head b == p then reverse moves else []
  else
    tryMoves nextMoves
  where
    nextMoves       = possibleMoves b
    tryMoves []     = []
    tryMoves (m:ms) =
      let result = play (move b m) p (m:moves)
      in if null result then tryMoves ms else result

-- Compute the initial empty position to know the goal, then solve the puzzle
solve b = let emptyPos = head [ (r,c) | r <- [0..4], c <- [0..r], isEmpty b (r,c) ]
          in play b emptyPos []

-- A sample board with the topmost hole empty
board :: Board
board = [ (1,0), (1,1),
          (2,0), (2,1), (2,2),
          (3,0), (3,1), (3,2), (3,3),
          (4,0), (4,1), (4,2), (4,3), (4,4) ]

main = print (solve board)

I made a number of Google searches of the forms below and averaged the results:

"implemented in <language>"
  "written in <language>"

Naturally this is of very limited utility, and the numbers are only useful when comparing relatively within one column since the number of results Google returns can vary greatly over time.

¹ combines Lisp, Scheme, Common Lisp, Arc & Clojure
² combines OCaml, (S)ML, Caml
³ summed separate searches for sml and ml

I made a number of Google searches of the forms below and averaged the results:

"implemented in <language>"
"written in <language>"

¹ combines Lisp, Scheme, Common Lisp, Arc & Clojure
² combines OCaml, (S)ML, Caml
³ summed separate searches for sml and ml

Haskell The Hope Of The Statically Typed Family

After many hours of research and a brief dive into Standard ML, I’ve selected Haskell as the best candidate for me to evaluate statically typed functional programming languages. At this point, I’m subjectively biased against statically typed functional programming languages because of the enjoyment and productivity I’ve found in Ruby & Lisp, but my only experience with statically typed languages (C, C++, Java) has not been representative of good statically typed languages, so I’m reluctant to form a strong opinion of static typing before I’ve become proficient in a good statically typed language.

There are, of course, a number of respected statically typed functional programming languages, but I think Haskell provides me with the best opportunity to make a personal assessment regarding the benefits of static typing for my particular situation, and I think someone would be hard pressed to convince me that it’s a poor choice objectively.

There Can Be Only One

After working halfway through Programming in Standard ML by Robert Harper, I realized that I enjoy the language and it seems simpler & cleaner than Haskell, but I also realized that I only have time to become truly proficient in one statically typed functional programming language in the near future. I feel that a reasonable level of proficiency is required to evaluate a language well. I have seen many examples of someone, with only a little knowledge of a programming language, making an unfounded criticism of a programming language, or a particular feature, only to be corrected with an accurate, elegant and convincing counter argument by someone who is experienced with the language.

A quick survey of a language won’t be enough for me to make a decision on some key points such as static vs. dynamic, nonstrict vs. strict, pure vs. impure, etc. as well as important peripheral issues such as existing libraries, tools, etc. – it’s going to require understanding some of the subtleties of the language and writing enough code to get a feel for the language, so I felt I needed to limit my choice to one statically typed FPL.

Static vs. Dynamic

Clearly both static and dynamic typing work well for large numbers of people. One of my goals is simply to answer the static vs. dynamic question for myself given my preferences and the type of software I want to develop. I’d previously decided to learn both Standard ML and Haskell, so my reasons below for choosing Haskell are primarily with respect to comparing the two languages:

Haskell Is Pure And Lazy

I’m already familiar with impure, or multi-paradigm, programming languages that offer some functional features but allow imperative programming, so being forced to program in a purely functional manner and abandon my comfort zone of imperative patterns is an advantage for me. I have no experience with lazy languages, so Haskell offers an opportunity to gain more experience with laziness :).

In some respects, Haskell is more different than Lisp compared to other statically typed functional programming languages, so it’s a good point of comparison. It may end up being the ultimate death match :)

• Static vs. Dynamic
• Nonstrict vs. Strict
• Rich/Complex Syntax vs. Simpler Syntax
• Pure vs. Impure/Multi-paradigm

Active Community

Haskell has a very active community. Although I’m skeptical about whether a statically typed functional programming language will be suitable for the type of work I want to do with it, it makes sense to choose one that has a reasonable shot, and I don’t personally feel that Standard ML does – it was mainly to be an introduction to functional programming and a stepping stone to another FPL.

Part of the reason I don’t feel that Standard ML has a reasonable shot is that it feels dated and somewhat abandoned. Functional programming languages are niche languages to begin with, but it seems that Haskell and OCaml both have fairly strong communities.

Cool Features

Although I think Haskell’s custom of continuing to add cutting edge research features into the language may have some disadvantages if not done well, i.e. making the language messier and complicated, for my primary purpose of evaluating the benefits of statically typed languages, I think having more advanced features is an advantage over Standard ML. If a language with such an active research community as Haskell fails to convince me of the benefits of static typing, then it may just not be for me.

Monads and type classes seem interesting, and Haskell provides an opportunity to learn them. Monads seem useful outside of Haskell, so the time spent learning about them can be leveraged. I already like list comprehensions, so it’s nice to have them available again.

Learning some of the advanced features of Haskell will be beneficial to me regardless of whether I continue programming in Haskell or decide to go with the Lisp family.

Textual Resources

Standard ML actually has a surprising number of good texts available, so I don’t think Haskell offers a big advantage here, but in my particular case, I already own two Haskell texts – Programming in Haskell by Graham Hutton and The Craft of Functional Programming by Simon Thompson. Also, Chris Okasaki’s Purely Functional Data Structures provides Haskell examples as does Richard Bird’s Introduction to Functional Programming using Haskell (2nd ed.). Lastly, I think Real World Haskell may be very helpful.

Haskell Crash Course

My goal now on the statically typed front is to become as proficient in Haskell as I can in a very short period of time. There seem to be plenty of resources available, but if you’re aware of any particularly helpful resources or tips, feel free to add a comment.

After bumping into a number of local programmers who expressed an interest in functional programming, I thought it might be a good time to start a local group that focused on functional programming languages, so I did a couple days ago.

TriFunc.org is a group for programmers who are interested in functional programming languages and live near the Research Triangle area of North Carolina.

If you live in the area and have an interest in functional programming languages, feel free to dive in and start participating in the Google Group discussions. Once we reach a critical mass, I expect we’ll produce a meeting schedule, etc., but that will depend on where the group wants to take this.

The 2008 Programming Language Plan didn’t go as well as I hoped, so I’m regrouping for another go at it. I did make progress learning some Logo and teaching it to my daughters, and I worked through seven chapters of “Programming in Haskell” which was very enjoyable, but I also spent way too much time trying to decide which language(s) to learn without actually learning them.

I have now decided which languages I want to learn this year, so I figured I’d post this blog entry. In some respects, things haven’t changed much from last years plan, but my decisions are much less tentative which is encouraging. I’m glad to switch from information gathering to actually learning a few languages.

Motivation

When I switched from C++ to Java in 1996 and noticed a large increase in productivity; however, it didn’t occur to me to consider whether switching from Java to another language might also give me a similar boost in productivity. The job demand for Java was high during the 10 years I used it, and I was getting paid for my time vs. what I produced, so the oversight wasn’t too costly.

When I switched from Java to Ruby in 2006 I experienced a comparable, if not greater, boost in productivity as I had with the switch from C++ to Java. This time I considered the effect of programming language choice on productivity more carefully and began to wonder about the optimal programming language for me. As a small business owner, my primary consideration is productivity, not popularity or the interchangeableness of programmers.

I don’t think a perfect programming language exists in general, but I think there is an optimal language for me given my particular circumstances, the problems I want to solve, the type of software I want to develop, my way of thinking, my aesthetic tastes, etc.

The Problem

There is a cost to research programming languages to determine the optimal one, and there is a cost to switch programming languages, so the benefit of a new programming language needs to exceed those costs.

Additionally, a significant catch-22 exists in that to truly determine if a language is optimal, one must reach a level of proficiency with the language. There isn’t enough time to learn all of the candidate languages, so some filtering mechanism must be used first to narrow the choices to a reasonably small set. This filtering mechanism is theoretical by nature, but I think the subtle practicalities of a language have a significant effect on productivity.

I have a long term perspective for this task, so I don’t mind investing time researching programming languages, and I also don’t mind if I need to develop/acquire supporting libraries before being ultimately more productive than I am currently with Ruby and Rails.

The Process

I briefly entertained the idea of going about this research in a more systematic, scientific way. That might be a reasonable approach, but due to the following:

• My laziness
• The high degree of subjectivity in programming language choice
• The lack of consensus among programming language researchers

I ended up with a fairly ad-hoc approach involving examining the following areas and trying to absorb enough information to formulate a plan:

Efficiency

Programming language efficiency is becoming increasingly important to me as Moore’s law loses steam, and power & cooling issues become more prominent.

On the one hand, Ruby is near the bottom of the pack with respect to efficiency, but the productivity has been outstanding, and at the volume of transactions I’ve needed to deliver thus far, performance hasn’t been a problem.

On the other hand, if programming languages exist (and I believe they do) that have similar or greater power than Ruby but are compiled instead of interpreted, that would be an advantage.

Benchmarks are notoriously controversial with respect to the degree in which they predict performance, but I don’t think they’re irrelevant. One popular benchmark site is: Programming Language Shootout. I also created some micro-benchmarks of my own to test performance.

One negative result of Ruby being inefficient is the disparity in performance of code written in Ruby vs. library code, or extensions, written in C. This creates counter-intuitive scenarios where a piece of code that appears less efficient is actually more efficient because of the use of built-in code implemented in C. I don’t like thinking in those terms; I would much prefer that user written code in the language is much closer to the efficiency of built-in library code.

Concurrency

With the flattening of CPU MHz and proliferation of CPU cores, I think concurrency may continue to grow in importance. Although I develop mainly server side web applications which can take advantage of multiple cores by virtue of having multiple independent processes, I would prefer to have better concurrency mechanisms in the language/libraries directly.

Joy

I think I first heard joy used, in the context of programming languages, in the Ruby community – probably from Matz himself. I have to agree that programming in Ruby has been more joyful than previous programming languages.

I’m not sure exactly why this is, but I expect it has something to do with the effectiveness and productivity of Ruby, but it may be helped by the incredibly friendly Ruby community.

Fundamental Nature

My preference is for a programming language to minimize arbitrariness and to maximize orthogonality. In other words, I would prefer the language to have a minimal set of core concepts/axioms/operators/etc. that are built upon systematically.

Community

Whether my optimal language is mainstream or not is irrelevant to me, so I don’t need the programming language community to be large (and in fact, being too large is a detriment), but I do think it should be active enough that there are people available to help answer questions, write libraries, maintain/improve compilers, debuggers etc.

To this end, I spent time on various usenet groups, IRC channels and blogs. Occasionally asking questions, but mostly observing the dialog and interaction among the community members.

Education

What educational materials are available?

I tend to prefer learning from books, so searching Amazon to see what books are available, how well they’re received, etc. was helpful. Although I prefer books typically, in the exploratory stages, it’s cheaper to go through online materials, so searching the web for free PDFs was useful. The existence of a few good texts is also an indication of the vitality of community.

Productivity

Ultimately, I’m after the most productive language for me; however, I think productivity is the factor that requires the most proficiency with a language to judge, so it was the most difficult factor to research prior to learning a language. I was limited to anecdotal stories, case studies, personal testimonies, etc.

Licensing

I prefer open source licensing because I think programming languages with proprietary licensing are more likely to die.

The Final Candidates

I began with Ruby as the point of reference irrespective of Rails and other libraries. Even though Rails is an important factor in my current productivity, since I’m taking a long term view, I didn’t want to exclude a fantastic language simply because it’s lacking something that Ruby was also lacking N years ago.

Due to the cost of researching, learning and switching to a new programming language, I only considered languages that had the potential of offering a significant improvement in one or more areas without losing too much in other areas.

The candidates I eventually selected fell into two groups. Both groups have strong functional capabilities, good efficiency, and long, successful track records. I believe that even the best programming language designers make serious mistakes which can only be identified with the hindsight of years of use. It’s possible that someone is about to release a brand new language that has the potential to be the most productive for me personally; however, I’m not willing to take the risk to learn it.

The Lisp Family

Lisp has a very long track record of success and adaptability. In fact, if I was forced to program in a single programming language from now on, I would probably choose a Lisp since I think it would have the greatest likelihood of being able to adapt.

The Lisp family has dynamic typing which I’ve grown to love with Ruby, but most also allow type declarations for efficiency. Lisp also appears to have a more fundamental nature than most languages. I’ve heard it said that Lisp was more discovered than invented.

I first became interested in Lisp when I learned that Ruby was influenced by it. My interest was reinforced by some of Paul Graham’s essays & books. I like the exploratory and dynamic nature of developing Lisp – this is mostly from reading comments of others, but I’ve tasted a small part of this when evaluating Lisp code in Emacs and having it be available immediately.

Logo is first on the list simply because it’s both a Lisp and a great language for teaching children how to program, so I can kill two birds with one stone.

Scheme is next because it’s a natural sequel to Logo and I still want to work through “The Structure and Interpretation of Computer Programs”. The fact that Paul Graham chose mzcheme to create his Arc language is a good “letter of recommendation”. Scheme feels the most fundamental, simple & clean thus far.

Common Lisp is after Scheme due to its eminent practicality and completeness. It has plenty of warts, but also plenty of power and functionality. It’s been called a great, big, ball of mud – but in a good way ;)

Lastly, is Clojure. It’s last in the Lisp family because I want to learn Scheme & Common Lisp first so I’ll be better equipped to judge Clojure. This will also allow more time for Clojure to mature. Clojure has a focus on functional programming & concurrency that is symbiotic with the Java platform. The latter provides a quick start and access to Java libraries, the JVM infrastructure, etc., but my preference would be to not be dependent on the JVM in the long run. I’ll withhold judgment until I’ve learned it and used it for a while.

The ML Family

I’m least familiar with the ML family and with functional programming in general. I’ve spent most of my career studying and using imperative, object-oriented programming languages.

I think the ML family is worth studying because:

• Functional programming may be beneficial with respect to concurrency.
• Prog. Lang. researchers seem to be enamored with ML family.
• There are enough anecdotal testimonies of productivity to warrant further study.

Standard ML is an important functional language that differs from Haskell in that it’s impure, i.e. it allows side effects, and it’s strict, i.e. not lazy. It shares Hindly-Milner static typing with Haskell. The community seems rather tiny, and I expect that if I go with a static typed language it will likely be Haskell, but I wanted to learn Standard ML first because of its historical importance and to be able to compare an impure/strict language with a pure/nonstrict language.

Haskell is probably the most different programming language from what I’m used to. This, in and of itself, has some advantages with respect to gaining new perspectives and ideas. In some ways, it’s a language that has taken things to extremes with respect to functional purity and laziness.

The community is very active. It offers a great compiler (GHC), software transactional memory, a decent base of libraries, etc.

At this early stage, I’m skeptical of static typing, functional purity and laziness, so becoming proficient in Haskell is a great opportunity to be able to determine how I feel about those.

The Plan

Rather than go through the candidates sequentially, I’m going to try and make progress on two tracks concurrently to allow me to compare concepts from both families:

I’m curious to find out how I feel about these languages after I’ve achieved some skill with them, but I think becoming proficient in the Lisp and ML families will be time well spent. At minimum, I’ll be better equipped to compare other languages.

"implemented in <language>"
"written in <language>"

I’m very curious to see how these stats change over time, so I’ve added a calendar item to recompute them in six months. Leave a comment if you’d like to add a programming language to the list, and I’ll update this article and it will be included in the recomputation six months from now.

¹ combines Lisp, Scheme, Common Lisp, Arc & Clojure
² combines OCaml, (S)ML, Caml
³ summed separate searches for sml and ml
Update 4/23/09 added C#, Tcl per comment requests.

This one was too much fun for words in re how cool it is programming
with Lisp. I would like to see this in Ruby, Clojure, Qi, and
Scheme. The precise fun part tho is typing it all in in the final form
versus dividing the thing up into steps to get intermediate results,
ie, a test of one's mastery of one's language. Non-functional
languages I guess have no choice but to stop and assign temporaries.

Given:

(defparameter *pets*
  '((dog ((blab 12)(glab 17)(cbret 82)(dober 42)(gshep 25)))
    (cat ((pers 22)(siam 7)(tibet 52)(russ 92)(meow 35)))
    (snake ((garter 10)(cobra 37)(python 77)(adder 24)(rattle 40)))
    (cow ((jersey 200)(heiffer 300)(moo 400)))))

Write:

(defun digest-tag-population (tag-population pick-tags count)...)

Such that:

(digest-tag-population *pets* '(dog cat snake) 5)

=> ((DOG CBRET 82) (DOG DOBER 42) (CAT RUSS 92) (CAT TIBET 52) (SNAKE
PYTHON 77))

...the rules being:

- consider only the populations of tags (the first symbol in each
sublist) found in the parameter pick-tags, a list

- take only the  most populous of the union of the populations

- return (tag name population) of the most populous in this order:

    firstly, by position of the tag in pick-tags
    second, ie within a tag, in descending order of population

(defun subseq-ex (st e s)
  (subseq s st (min e (length s))))

(defun digest-tag-population (tag-population pick-tags count)
  (flet ((tagpos (tag) (position tag pick-tags)))
    (stable-sort (subseq-ex 0 count
                   (sort (loop for (tag population) in tag-population
                             when (tagpos tag)
                             append (loop for pop in population
                                        collecting (list* tag pop)))
                     '> :key (lambda (x)
                               (caddr x))))
      '< :key (lambda (x) (tagpos (car x))))))

(defparameter *pets*
  '((dog ((blab 12)(glab 17)(cbret 82)(dober 42)(gshep 25)))
    (cat ((pers 22)(siam 7)(tibet 52)(russ 92)(meow 35)))
    (snake ((garter 10)(cobra 37)(python 77)(adder 24)(rattle 40)))
    (cow ((jersey 200)(heiffer 300)(moo 400)))))

#+test
(digest-tag-population *pets* '(dog cat snake) 5)

And here is my Ruby version:

PETS = [
  [:dog, [[:blab, 12], [:glab, 17], [:cbret, 82], [:dober, 42], [:gshep, 25]]],
  [:cat, [[:pers, 22], [:siam, 7], [:tibet, 52], [:russ, 92], [:meow, 35]]],
  [:snake, [[:garter, 10], [:cobra, 37], [:python, 77], [:adder, 24], [:rattle, 40]]],
  [:cow, [[:jersey, 200], [:heiffer, 300], [:moo, 400]]]
]

def digest_tag_population tag_population, pick_tags, count
  tag_population.select {|e| pick_tags.include?(e[0]) }.
    inject([]) {|memo,obj| obj[1].each {|e| memo << [obj[0], e[0], e[1]] }; memo }.
    sort {|a,b| b[2] <=> a[2] }[0,count].
    sort_by {|e| [ tag_population.map{|p| p[0]}.rindex(e[0]), e[2] * -1] }
end

digest_tag_population(PETS, [:dog, :cat, :snake], 5)

Within the function:
Line 1: select elements that match the pick tags
Line 2: map to a list of tuples of the form [:dog, :blab, 12]
Line 3: sort the list of tuples by population and select the first count of them
Line 4: sort by tag position, population

Output:

[[:dog, :cbret, 82],
[:dog, :dober, 42],
[:cat, :russ, 92],
[:cat, :tibet, 52],
[:snake, :python, 77]]

I think Ruby compares very favorably. What do you think? Feel free to submit a version in another language.