[Oberon] Clarifying type compatibility in Oberon-07
Jörg
joerg.straube at iaeth.ch
Wed Oct 4 18:11:03 CEST 2017
In my point of view Appendix A for Oberon-07 would look like this.
Joerg
Appendix A: Definition of terms
Integer types BYTE, INTEGER, LONGINT (not official but compiler allows as
if LONGINT = INTEGER)
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
Integer types include (the values of) smaller numeric types according to the
following hierarchy:
LONGREAL >= REAL >= LONGINT = INTEGER >= BYTE
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 integer 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.
4. Tf is ARRAY n OF BYTE and Ta has length n.
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 1st op 2nd op result
type
+ – * numeric type numeric type numeric
type
/ real type real type real
type
+ – * / SET SET SET
DIV MOD integer type integer type integer
type
OR & ~ BOOLEAN BOOLEAN BOOLEAN
= # < <= > >= numeric numeric BOOLEAN
CHAR CHAR BOOLEAN
character array, string character array, string BOOLEAN
= # BOOLEAN BOOLEAN BOOLEAN
SET SET BOOLEAN
NIL, pointer type T0 or T1 NIL, pointer type T0 or T1 BOOLEAN
procedure type T, NIL procedure type T, NIL BOOLEAN
IN integer type 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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