Objective

The objective of the facility described here is to facilitate synthesis of type conversion between non-scalar types even if no direct conversion path exists between them or their component types.

Given v of vector type V with component type T1 and w of vector type W with component type T2 ...

TYPE
    V = OPAQUE RECORD ("V-Type") v1, v2, v3 : T1 END;
    W = OPAQUE RECORD ("V-Type") v1, v2, v3 : T2 END;

VAR
    v : V; w : W;

the conversion from v to w ...

w := v :: W;

should be synthesised by the compiler in the event that no direct conversion path exists from type T1 to type T2, as long as V and W have the same number of components.

Approach

The key to synthesising such a conversion is to decompose v into its components, serialise the components using conversion primitive toASCII of type T1, then deserialise the components using conversion primitive fromASCII of type T2 and finally compose w from the so converted components.

To facilitate this, the non-scalar types must provide

• a function to return the number of components or highest index
• an accessor function to return the n-th component of a vector
• a mutator procedure to overwrite the n-th component of a vector

The component type can be deduced form the return type of the accessor function.

This could be done using the following bindings:

PROCEDURE [HIGH] highestComponentIndex ( v : VECTOR ) : CARDINAL;
PROCEDURE [.] componentN ( n : CARDINAL; v : VECTOR ) : ComponentType;
PROCEDURE [!] setComponentN ( n : CARDINAL; VAR v : VECTOR; c : ComponentType );

An example is given in TypeSampleVector

The generalised synthesis algorithm is:

VAR v : V; w : W;
w := v :: W;

synthesises to =>

VAR v : V; w : W;
    index : CARDINAL;
    significand,
    exponent : ARRAY %MAX_LITERAL_LENGTH% OF CHAR;

IF HIGH(v) = HIGH(w) THEN
    FOR index := 0 TO HIGH(v) DO
        V.toASCII( %ACCESSOR%(index, v), %decOrHexT1%, significand, exponent );
        %MUTATOR%(index, w, W.fromASCII( %decOrHexT2%, significand, exponent ));
    END; (* FOR *)
END; (* IF *)

where %MAX_LITERAL_LENGTH% is a compiler constant designating the maximum length allowed for literals, %decOrHexT1% and %decOrHexT2% are boolean values indicating the radix system of a type's internal representation, %ACCESSOR% is the accessor function and %MUTATOR% is the mutator procedure.

NB: For the compiler to save stack space for the intermediate strings significand and exponent a means to obtain the exact required number of digits for a scalar type could be introduced. This is an optimisation issue and it has no impact on the semantics of the synthesis.