This is really elegant, although it's not very well-suited for statically typed languages. This is part of a Smalltalk scanner:

Scanner initialize
[
  super initialize.
  (charTable := Array new: 256)
    atAllPut: #xIllegal;
    atAll: '0123456789'                 asByteArray put: #xDigit;
    atAll: 'abcdefghijklmnopqrstuvwxyz' asByteArray put: #xLetter;
    atAll: 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' asByteArray put: #xLetter;
    atAll: '_'                          asByteArray put: #xLetter;
    atAll: '~!@%&*=\\?/><,|^' asByteArray put: #xLetter;
    atAll: '+-'                         asByteArray put: #xSign;
    ...
    at:    $'                           asciiValue  put: #xString;
    at:    $"                           asciiValue  put: #xComment.
]

Scanner scan
[
  ...
  c notNil ifTrue: [self perform: (charTable at: c value)].
  ...
]

Scanner xSign
[
  ^context peek isDigit
    ifTrue: [self xDigit]
    ifFalse: [self xBinary]
]

...etc

Source: The FONC repository, Scanner.st by Ian Piumarta. License: 'AS IS'.

How it works:

1. Character 'a' is passed.
2. Object looks up which method to use in that case.
3. The object retrieved the result of that lookup.
4. The object calls the method on itself.

The advantage? You can avoid these ridiculously large switch-like constructs. Also note the concise way in which the table is constructed. svn praise!

A description of the same technique applied in Python can be found in this python pattern collection.