Ch 5: Basic Semantics
-----------------------

Semantics: describes the meaning of programs
-- operational Vs denotational
-- formal Vs informal

Semantics is typically defined in a bottom-up fashion:
  -- values
  -- names
     -- variables
     -- constants
  -- expressions
  -- statements
  -- compound statements
  -- procedures
  -- program

5.1 Attributes, Binding, and Semantic Functions

Meanings of names is captured via attributes associated with the names:
    -- type
    -- value
    -- location

Binding: establishing an association between name and an attribute
 -- binding time
  -- static 
    -- language definition time
    -- lang impl time
    -- compile-time
    -- link time
    -- load time
  -- dynamic
 Eg: type is statically bound in most langs
     value is dynamically bound
     location may be dynamically or statically bound

Bindings are held in
  -- symbol table: name --> static attributes
  -- environment: name --> locations
  -- memory: locations --> value

Declarations Blocks and Scopes
-------------------------------

Scope: region of program over which a declaration is in effect
       ie bindings established by decl must be maintained
  global
  package or module
  file
  class
  procedure
  block

Block-structured, lexically-scoped language

Visibility:
  redefinitions in inner scopes supercede outer definitions
  qualifiers may be needed to make otherwise invisible names to be visible 
    in a scope
  Eg:
   local var superceding global var
   names in other packages
   private members in classes