[silentbicycle]

For one thing, the pattern matching used in Erlang, ML, and Haskell can be quite easy to read.

For example, something like

  let days_in_month m = match m with
    | Jan | Mar | May | Jul | Aug | Oct | Dec -> 31
    | Apr | Jun | Sept | Nov -> 30
    | Feb -> if leap_year () then 29 else 28

It takes a small amount of context (all "| Val" sections without a -> ... side match together), but it's a pretty direct correspondence.

[nostrademons]

That's not much harder in C or Java, given appropriate enum declarations:

  public int days_in_month(month) { 
    switch(month) {
       case JAN:
       case MAR:
       case MAY:
       case JUL:
       case AUG:
       case OCT:
       case DEC:
         return 31
       case APR:
       case JUN:
       case SEPT:
       case NOV:
         return 30;
       case FEB:
         if(leap_year()) return 29; else return 28;
     }
  } 

Pattern-matching really shines when you need to destructure the argument, then do something similar to the result regardless of which case resulted in the destructuring. For example, compare red-black trees written in Java:

http://www.docjar.com/html/api/java/util/TreeMap.java.html

vs. those written in Haskell:

http://www.cse.unsw.edu.au/~dons/data/RedBlackTree.html

The rebalancing code in Java is 80 lines long. The rebalancing code in Haskell is 6.

[silentbicycle]

I couldn't think of a better example at the time. Something that simultaneously matched several fields (whether destructured from one variable or not) and/or had guards would be a better example.

Maybe something like this (in pseudo-ML):

  (* Look up order code for a Sci-Fi GadgetTM, units are in cm *)
  let gadget_order_code width depth height color has_laser =
    match (width depth height color has_laser) =
       (* The original, simple code *)
      | 5, 2, 1, Red, true -> "ZAP-X"
       (* Most common width, color *)
      | 4, d, h, Blue, true -> sprintf "ZAP-4-%d%d+" (str d) (str h) "+"
       (* C for Custom Color *)
      | 4, d, h, c, false -> "ZAP-4C-%d%d-%c" (str d) (str h) (color_code c)
       (* Orange lasers are discontinued *)
      | w, d, h, c, true when (w + d + h) < 15 and c != Orange ->
         "ZAP-S-%d%d%d-%c" (str w) (str d) (str h) (color_code c)
      | _, _, _, _, _ -> failwith "Unavailable"

That's a little complicated to determine with pattern matching or via a database, but doing it in a series of nested if statements would get mind boggling.

[silentbicycle]

(oops. lost the sprintfs...)