Compatible Type:

• legal for operator
• allowed under language rule (implicitly converted - coercion)

Type Binding are Static  -   Type checking done by compiler.
Type Binding are Dynamic - Run time checking type.

Strong Typing:
        If typed errors are always detected either at compile time or run time.

    examples:

Not strongly typed

FORTRAN - the relationship between actual and formal parameters is not type checking.
                    the use of EQUIVALENCE allows one variable to refer to a value of different type.
C, C++ - functions do not have to have parameter type checked.
              UNION types are not type checked.

Nearly strongly typed

Pascal - good, except variant records.
Ada - dynamically checks for correct types values
      - use UNCHECKED_CONVERSION to get rid of checking.
Modula-3   - LOOPHOLE same as UNCHECKED_CONVERSION in Ada.

Strongly typed

ML - all variables have statically know type.
JAVA - based on C++, like Ada (in terms of type checking)
            Error can occur explicitly, not implicitly.

        There are two methods for checking type compatibility.

1. NAME TYPE:   the type name must match.
2. STRUCTURE TYPE:   underlying structure must match.

e.g.
       type   indextype = 1.. 100;      {a subrange type}
       var
                count : integer;
                index : indextype;

     count and index are not NAME TYPE compatible.  It is STRUCTURE TYPE compatible.

e.g.
       type
          type1 = array [1..10] of integer;
          type2 = array [1..10] of integer;
          type3 = type2;

   If we do not use STRUCTURE TYPE compatibility, type1 and type2 are not compatible.
      Using declaration equivalence, we say type2 and type3 are compatible.

e.g.
     type celsius is new FLOAT;
     type fahrenheit is new FLOAT;

     By NAME TYPE compatibility, they are not same.
     Ada using derived type checking, gets avoid name type checking.

C:
     use structure equivalence except for record & union (these two are declaration equivalence)
C++:
    use name equivalence.
FORTRAN:
    can not use name equivalence.
COBOL:
    can not use name equivalence.
    can not define and name types.