Kinds of Symbols

A compiler must typically deal with several different kinds of symbols:

• Symbolic constants: const pi = 3.1415926
  Store constant value and type; convert an identifier with this name to a numeric constant as soon as it is looked up. The language may have some built-in symbolic constants, such as maxint.

• Enumerated types:
  type color = (red, white, blue);
  Simply assign constant values 0, 1, ... to the items. The name color becomes a subrange 0..2.

• Subrange types: type digit = 0..9;
  Store the associated scalar type and the lower and upper bounds (always integers).

• Scalar types:
  boolean integer real char pointer
  These are predefined as types in the symbol table.

• Variables: these may have scalar types or complex types.