From Modula-2 Reloaded

WiP: Verification Of Operator Bindings

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Semantic Superset Types

For a library defined type to define bindings to operators and pervasive functions it must be declared as a subset of one of six semantic superset types:

• the A-Type, semantic superset of all dynamic array and set types
• the S-Type, semantic superset of all dynamic character string types
• the Z-Type, semantic superset of all integer number types
• the R-Type, semantic superset of all real number types
• the C-Type, semantic superset of all complex number types
• the V-Type, semantic superset of all vector and ordered tuple types

The syntax is defined as:

recordType :
    RECORD ( '(' semanticType | baseType ')' )? fieldListSequence? END ;

opaquePointerType :
    OPAQUE ( '(' semanticType ')' )?;

semanticType : string ;
// "A-Type" and "S-Type" for opaque pointers
// "Z-Type", "R-Type", "C-Type", "V-Type" for records

The verification of operator bindings depends on the semantic type that a library type is declared a subset of. It is a compile time error to declare a binding for an operator or pervasive function that is not permitted by the type's semantic superset type.

The bindings permitted for each semantic type are listed below:

A-Type Bindings

The following bindings are permitted:

• [NIL] null key value
• [NEW] constructor
• [DISPOSE] destructor
• [COUNT] number of entries
• [FOR] iterator
• [IN] membership test
• [.] entry accessor
• [!] entry mutator
• [-] entry removal

Example: SampleCollection

S-Type Bindings

The following bindings are permitted:

• [NEW] constructor
• [DISPOSE] destructor
• [LENGTH] length
• [:=] literal assignment
• [::] type conversion
• [+] concatenation
• [=] equality
• [<] lower in collating sequence
• [>] higher in collating sequence

Example: STRING

Z-Type Bindings

The following bindings are permitted:

• [TMIN] minimum value
• [TMAX] maximum value
• [ABS] absolute value
• [NEG] sign reversal
• [ODD] odd or even
• [:=] literal assignment
• [::] type conversion
• [+] addition
• [-] subtraction
• [*] multiplication
• [DIV] division
• [MOD] modulo
• [=] equality
• [<] less than
• [>] greater than
• [TO] scalar conversion primitive
• [FROM] scalar conversion primitive

Examples: SampleUINT and SampleINT

R-Type Bindings

The following bindings are permitted:

• [TMIN] minimum value
• [TMAX] maximum value
• [ABS] absolute value
• [NEG] sign reversal
• [:=] literal assignment
• [::] type conversion
• [+] addition
• [-] subtraction
• [*] multiplication
• [/] division
• [=] equality
• [<] less than
• [>] greater than
• [TO] scalar conversion primitive
• [FROM] scalar conversion primitive

Example: BCD

C-Type Bindings

The following bindings are permitted:

• [ABS] absolute value
• [NEG] sign reversal
• [::] type conversion
• [+] addition
• [-] subtraction
• [*] multiplication
• [/] division
• [=] equality

Example: COMPLEX

V-Type Bindings

The following bindings are permitted:

• [HIGH] highest component index
• [ABS] absolute value
• [NEG] sign reversal
• [.] component accessor
• [!] component mutator
• [::] type conversion
• [+] addition
• [-] subtraction
• [=] equality

Example: SampleVector and SampleTuple

Common constraints

The following constraints are common to all semantic types:

• a module can only define bindings for a type that is declared in the module and has the same identifier as the module.
• multiple type conversion bindings may be declared but only if each binding has a different conversion target type.
• any other bindings can only be declared once.

Summary