Tuesday, 14 April 2009

Extending the Gen Runtime

I thought it would be worthwhile describing how we have extended the Gen runtime in the development of our tools, but first we should clarify what we mean by the ‘runtime’.

A high level language (including Gen, but also languages like C, COBOL, Java, .Net, etc,) simplifies the developer’s task by providing functions that are inherent in the programming language. Examples include printf in C, STRING in COBOL and the Gen concat function.

The actual implementation of the function by the compiler (or code generator) might be via a macro, code generation (i.e. the COBOL or C compiler generating assembler instructions to implement the statement) or via a call to a language runtime module. To the developer, it does not matter how the function is implemented. For example, the CA Gen concat function is implemented in generated COBOL code whereas in C it is implemented via a Gen runtime function call.

So what is the difference between a language’s runtime functions and those that you might procure from a 3rd party vendor or develop in-house?

From a developer’s perspective, in some languages (like C) the code to use a language function will not differ much from the code to use a 3rd party function, whereas in others (like COBOL), the in-built functions are typically referenced via language statements (i.e. STRING) whereas other functions would be used via a CALL statement. Typically a function that is invoked via simple language statements is easier to use than having to implement a separate program call to invoke the function.

In CA Gen action diagramming, the same is true. Compare the following:

SET c to numtext(substr(concat(a,b),1,5))

With the following which uses alternative routines for numtext, substr and concat.

SET map_1 TO a
SET map_2 TO b
USE my_concat
WHICH IMPORTS: map_1, map_2
SET map_4 TO map_3
SET start to 1
SET end to 5
USE my_substr
WHICH IMPORTS map_4,start,end
SET map_6 to map_5
USE my_numtext
SET c to map_7

In the first example, one statement could achieve the desired result, whereas if we replace the use of in-built functions with external action blocks that achieve the same result, we need a lot of additional code as well as special ‘mapper’ views that are of the same type as the import and export views of the EABs.

In the above example, I have shown an extreme case where each function has its own set of import and export vies that are not shared between the functions.

Gen allows you to develop your own functions, so you could then code the above as:

SET c to my_numtext(my_substr(my_concat(a,b),1,5))

We have made use of this capability to add our own functions into the Gen model and hence simplify our code, both in terms of the number of statements needed to implement a given task, but also reducing the number of ‘mapping’ views needed.

In a subsequent posting, I will describe some of the functions that we have developed.

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