ITEC 380 2013fall ibarland aaray

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lect01
Why study programming languages?

You can never understand one language until you understand at least two.
—John Searle

The limits of my language are the limits of my world.
—Ludwig Wittgenstein

Why study programming languages?

• learn other approaches; lets you understand your native tongue better;
• practice at learning new technologies/ideas;
• makes you think about: when is language helping, and when getting in the way; e.g. sorting: scheme vs Java
• Help you choose a language appropriate to the task

Discuss: You've used Java, and (others like) Ada, and javascript, and php, and C. What are features of Java you like, and when are you writing something where the language feels like it's getting in the way?

• When you read input from the user, and need to make sure it's an integer in [70,80).
• You want to sort a list of strings (say, all the state-names that your company has a "business presence" in).
  • First: how do we just represent this data? (what type?) Note: avoid the double-bracket “notation for initializing” as mentioned on some blog posts — it's doing something very different that happens to include the initializatlin you want, but (by creating anonymous inner classes) is also doing things you don't want. Or better: or the same thing indented differently:
  • Okay, how do we sort that, alphabetically?
• You want to sort a list of Memes.

  class Meme { File imageFile; // e.g. first-world-problem.jpg or mostInterestingManInTheWorld.gif String topText; String bottomText; }

  Sorting involves first by timestamp of imageFile, resolving ties by topText, resolving ties by bottomText. Or, in a different language: Racket:

  Writing this in racket, though, makes me think: Hey, < can be applied not just to exactly two arguments (inputs), but to any number of inputs: For example (< 2 3 4) is true, and (< 2 3 99 4) is not. Gee, shouldn't I write a version of meme<? which can take in any number of memes, and say whether or not they're ordered? It turns out, since racket evolved from a language for list-processing, this isn't so difficult after all. By mid-semester, you'll be able to write racket code like this: It's worth noting that this generalization in Java (pre-Java-8) is

  1. More verbose — each map needs to be a for-each loop —

  2. Not as generally useful (!): because generalizing from 2 to an entire list (collection) is so much harder, other people haven't written handy library functions that can make use of this more general code!

     This is a serious point: becase map is so easy to use, racket programmers use it all the time. Java programmers can do the same thing, but because it has (just) a couple extra lines of overhead per use, they don't, and even if they did take the time to write more general code it won't get leveraged by others.

• What if you want to sort Memes in different ways, depending: sometimes by date of file, but sometimes by just the text, sometimes ... .

Three ways to consider, in a language:

• Syntax (what strings are legal programs?)
• Semantics (what is the meaning of the program?)
• Pragmatics (what is in/convenient and un/suprising, about different syntactic constructs, and their semantics)

Families of languages:

• low-level
• procedural
• object-oriented
• scripting
• functional
• declarative

Reading: Chapter 1, by Friday.

Note: Book; add/drop.

A history overview
  name  yr  family  feature(s)/notables  (descendents/related)  example
  TM, lambda calculus 
  machine / hardware switches (incl. Babbage's Analytic Engine)
  assembly
  Lisp; Scheme, ML, Haskel, F#
  Fortran; PL/I; Algol; 
  SmallTalk; C++, java, C#
  Ada; 
  sh, csh, Tcl/Tk, perl, python, ruby
  rpn; postscript (printer is the interpreter; req'd M68000, not 8088,6502); pdf
  prolog (Japanese "4th wave")
  Basic (Apple II ROM; line#s; goto;'gosub' but no params (only globals) (recursion?!)), 
     http://www.jenutech.com/images/HomeSweetGoto10.gif
     http://theinfosphere.org/File:Gotohell.jpg
  Pascal (teaching; nested procedures)

  language popularity index
  poster: programming languages history
  The hello world collection

- examples: enscript -o foo.ps       (wimpout.ps)
      Example: enscript -o foo.ps ; cat foo.ps ; open foo.ps
      Example: cat wimpoutBoard.ps ; open wimpoutBoard.ps
   also, sh: Example: cd ~/Unix 
                      find . -name \*.ps -print
                      find . -name \*.ps -print | grep -i wimpout

- other notables:
  * postscript
  - C, Ada, Fortran, Pascal, Rexx, ...
  - Smalltalk, Java, C++, C#, ...
  - APL; Mathematica; Matlab
  
  - javascript, perl, etc;   html ?  -- no; data.  But, .css.
  - sh/csh, .bat, applescript; scriptable photoshop?
     Example: cd ~/Unix 
              find \*.ps
              find \*.ps | grep -i wimpout
     Note that we are calling functions.  (How are arguments passed?)
  - a *programmable* calculator.
  * MS Word "macros" and mailing-list scripts
  - abacus-instructions ?

Link: "A new language for phone networks" (declarative; based on F#)
www.technologyreview.com/communications/23330/?a=f

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©2013, Ian Barland, Radford University Last modified 2013.Aug.26 (Mon)

Please mail any suggestions (incl. typos, broken links) to ibarlandradford.edu