LANGUAGES

def: A *language* is
   a set of strings of characters
   (from some alphabet)

Characters are:
 For a human language:
   alphabetical characters
     (a, b, c, ...)
 For a computer (language):
   codes in some character set
   (ASCII characters or unicode)


          LANGUAGE CLASSES

Languages can be classified by
   the kind of grammar needed
   to recognize them



Venn Diagram:

 |--------------------------------------|
 | Regular Languages                    |
 |                                      |
 |                                      |
 |  |--------------------------------|  |
 |  | Contex-free Languages          |  |
 |  |                                |  |
 |  |                                |  |
 |  |  |--------------------------|  |  |
 |  |  | Context-sensitive        |  |  |
 |  |  |   Languages              |  |  |
 |  |  |                          |  |  |
 |  |  |                          |  |  |
 |  |  |  |--------------------|  |  |  |
 |  |  |  |  Type 0 Languages  |  |  |  |
 |  |  |  |                    |  |  |  |
 |  |  |  |                    |  |  |  |
 |  |  |  |                    |  |  |  |
 |  |  |  |                    |  |  |  |
 |  |  |  |                    |  |  |  |
 |  |  |  |--------------------|  |  |  |
 |  |  |                          |  |  |
 |  |  |--------------------------|  |  |
 |  |                                |  |
 |  |--------------------------------|  |
 |                                      |
 |--------------------------------------|


          PHASES OF A COMPILER

Programs allowed by a compiler's:

 |--------------------------------------|
 | Lexical Analysis (Lexer)             |
 |      regular grammar                 |
 |                                      |
 |  |--------------------------------|  |
 |  | Parser                         |  |
 |  |   context-free grammar         |  |
 |  |                                |  |
 |  |  |--------------------------|  |  |
 |  |  | Static Analysis          |  |  |
 |  |  |                          |  |  |
 |  |  |   context-sensitive      |  |  |
 |  |  |       grammar            |  |  |
 |  |  |  |--------------------|  |  |  |
 |  |  |  |  Runtime checks    |  |  |  |
 |  |  |  |                    |  |  |  |
 |  |  |  |    type 0 grammar  |  |  |  |
 |  |  |  |                    |  |  |  |
 |  |  |  |                    |  |  |  |
 |  |  |  |                    |  |  |  |
 |  |  |  |--------------------|  |  |  |
 |  |  |                          |  |  |
 |  |  |--------------------------|  |  |
 |  |                                |  |
 |  |--------------------------------|  |
 |                                      |
 |--------------------------------------|

    3*4+2
       (3*4) + 2

       3  * (4+2)