Evaluation of an external routine: eval

Syntax

eval ( externalRoutineName ( { argument } { , argument }* ) language languageName returns outputType )

Input parameters

externalRoutineName	the name of an external routine
argument	the arguments passed to the external routine
language	the implementation language of the routine
outputType	the data type of the object returned by eval (see outputParameterType in Data type syntax)

Examples of valid syntaxes

eval(routine1(DS_1) language “PL/SQL” returns string)

Semantics for scalar operations

This is not a scalar operation.

Input parameters type

externalRoutineName

name

argument

any data type

language

string

outputType

any data type restricting Data Set or scalar

Result type

result

dataset

Additional Constraints

The eval is the only VTL Operator that does not allow nesting and therefore a Transformation can contain just one invocation of eval and no other invocations. In other words, eval cannot be nested as the operand of another operation as well as another operator cannot be nested as an operand of eval
The result of an expression containing eval must be persistent
externalRoutineName is the conventional name of a non-VTL routine
The invoked external routine must be consistent with the VTL principles, first of all its behaviour must be functional, so having in input and providing in output first-order functions
argument is an argument passed to the external routine, it can be a name or a value of a VTL artefacts or some other parameter required by the routine
The arguments passed to the routine correspond to the parameters of the invoked external routine in positional order; as usual the optional parameters are substituted by the underscore if missing. The conversion of the VTL input/output data types from and to the external routine processor is left to the implementation.

Behaviour

The eval operator invokes an external, non-VTL routine, and returns its result as a Data Set or a scalar. The specific data type can be given in the invocation. The routine specified in the eval operator can perform any internal logic.

Examples

Assuming that SQL3 is an SQL statement which produces DS_r starting from DS_1:

DS_r := eval( SQL3( DS_1 ) language “PL/SQL”
        returns dataset { identifier<geo_area> ref_area,
                            identifier<date> time_,
                            measure<number> obs_value,
                            attribute<string> obs_status } );

Assuming that f is an externally defined Java method:

DS_r := DS_1 [calc Me := eval ( f (Me ) language “Java” returns integer) ];