Appendix A: Definition of terms
Integer types
SHORTINT, INTEGER, LONGINT
Real types
REAL, LONGREAL
Numeric types
integer types, real types
Same types
Two variables a and b with types Ta and Tb are of the same type if
  1. Ta and Tb are both denoted by the same type identifier, or
  2. Ta is declared to equal Tb in a type declaration of the form Ta = Tb, or
  3. a and b appear in the same identifier list in a variable, record field, or formal parameter declaration and are not open arrays.
Equal types
Two types Ta and Tb are equal if
  1. Ta and Tb are the same type, or
  2. Ta and Tb are open array types with equal element types, or
  3. Ta and Tb are procedure types whose formal parameter lists match.
Type inclusion
Numeric types include (the values of) smaller numeric types according to the following hierarchy:

LONGREAL >= REAL >= LONGINT >= INTEGER >= SHORTINT

Type extension (base type)
Given a type declaration Tb = RECORD(Ta)...END, Tb is a direct extension of Ta, and Ta is a direct base type of Tb. A type Tb is an extension of a type Ta (Ta is a base type of Tb) if
  1. Ta and Tb are the same types, or
  2. Tb is a direct extension of an extension of Ta
If Pa = POINTER TO Ta and Pb = POINTER TO Tb , Pb is an extension of Pa (Pa is) a base type of Pb ) if Tb is an extension of Ta.
Assignment compatible
An expression e of type Te is assignment compatible with a variable v of type Tv if one of the following conditions hold:
  1. Te and Tv are the same type;
  2. Te and Tv are numeric types and Tv includes Te;
  3. Te and Tv are record types and Te is an extension of Tv and the dynamic type of v is Tv;
  4. Te and Tv are pointer types and Te is an extension of Tv;
  5. Tv is a pointer or a procedure type and e is NIL;
  6. Tv is ARRAY n OF CHAR, e is a string constant with m characters, and m < n;
  7. Tv is a procedure type and e is the name of a procedure whose formal parameters match those of Tv.
Array compatible
An actual parameter a of type Ta is array compatible with a formal parameter f of type Tf if
  1. Tf and Ta are the same type, or
  2. Tf is an open array, Ta is any array, and their element types are array compatible, or
  3. Tf is ARRAY OF CHAR and a is a string.
Expression compatible
For a given operator, the types of its operands are expression compatible if they conform to the following table (which shows also the result type of the expression). Character arrays that are to be compared must contain 0X as a terminator. Type T1 must be an extension of type T0: 
operator  first operand       second operand      result type
+ - *     numeric             numeric             smallest numeric
                                                  type including
                                                  both operands
/         numeric             numeric             smallest real type
                                                  type including
                                                  both operands
+ - * /   SET                 SET                 SET
DIV MOD   integer             integer             smallest integer type
                                                  type including
                                                  both operands
OR & ~    BOOLEAN             BOOLEAN             BOOLEAN
= # <     numeric             numeric             BOOLEAN
<= > >=   CHAR                CHAR                BOOLEAN
          character array,    character array,    BOOLEAN
          string              string
= #       BOOLEAN             BOOLEAN             BOOLEAN
          SET                 SET                 BOOLEAN
          NIL, pointer type   NIL, pointer type   BOOLEAN
          T0 or T1            T0 or T1
          procedure type T,   procedure type T,   BOOLEAN
          NIL                 NIL
IN        integer             SET                 BOOLEAN
IS        type T0             type T1             BOOLEAN
Matching formal parameter lists
Two formal parameter lists match if
  1. they have the same number of parameters, and
  2. they have either the same function result type or none, and
  3. parameters at corresponding positions have equal types, and
  4. parameters at corresponding positions are both either value or variable parameters.
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