Multi-Pass System and Method for Source to Source Code Translation

This invention relates to a system and the method implemented therein for the translation of programs from one source code to another source code for compilation into the machine language of a data processing system and more particularly to such method and implementation for the translation of business oriented program languages.

Since various information processors are designed to be driven by their own particular machine language instructions or object code, the desire for program compatibility between processors has led to the creation of a number of higher level program languages which for the most part are machine independent. In order to accommodate such machine independent languages, the various information processors are provided with compiling routines as a part of their operating systems, which routines accept programs written in particular higher level languages and in turn compile the strings of machine language instructions or operation code to implement the particular program.

A particular higher level language adapted to the needs and requirements of business and accounting procedures is the COBOL language which name is an acronym for Common Business Oriented Language. COBOL is a general algorithm-specifying language with a structure such that instructions may be written in terms similar to terms in the English language which are readily comprehensible. It will be understood that because of the generality of this language, rather complex strings of machine instructions will have to be called forth to implement a particular COBOL instruction and that the complexity in length of such machine language strings would vary from processor to processor.

A particular higher level language which is similar in form to COBOL but which is nevertheless designed for very specific types of programming tasks such as reporting and business data file maintenance is the Report Program Generator which is more commonly known as RPG. Because of its simplicity and compactness, RPG is employed in many very small data processing systems. However, should the user decide to change to a larger data processing system for which RPG compiler is not provided, then his programs must be rewritten in the more general COBOL language or some other conversion technique must be provided.

The provision of a translation technique not only frees the user from being tied into his RPG program but it also provides the convenience of allowing the user to continue to write his programs in the more simple RPG language, where applicable for later translation into COBOL for use in a larger data processing system for which COBOL compilers are provided.

Various attempts have been made in the past to create translation or source to source conversion systems. However, because of the different meanings of a respective procedure statements as well as because of the different procedure formats, such systems were not very successful and required the user to manually correct inherent inconsistencies before he could achieve a workable program conversion. Of course, certain higher level languages such as ALGOL are so different in format and purpose from the COBOL language that conversion is not practical or even desirable. However, RPG and COBOL are similar in purpose and form so that a meaningful translation system can be realized. Yet even here, there have been sufficient differences between the two languages such that substantial reworking of the converted form is required to achieve an error free program that could be employed with the system having COBOL compiler.

It is, therefore, an object of the present invention to provide an automatic system for the translation of programs from one higher level program language to another higher level program language.

It is another object of the present invention to provide an improved translation system for the particularly accurate translation of programs from one source language to another source language even though particular statements and procedures in the respective languages differ in both form and significance.

It is still another object of the present invention to provide an improved translation system for the translation of programs from the RPG source language to the COBOL source language.

In order to accomplish the above described objects, the present invention resides in a system embodied in a data processor which system is adapted to receive a program in a particular higher level language form, and to read the records in sequence and in turn generate the data declarations and to build tables which are necessary for subsequent use of the converted program and to store such tables and the like in an intermediate file; to make a second pass through the initial program source code to determine and generate, in the second source language, the respective procedures and operations; and then to make a third pass through the initial source code and in response thereto to generate the respective routines which are required to complete the program in the second source language. Before the first pass, an initial pass is made to check the syntax of the program in the initial source code.

A feature then of the present invention resides in a system for translation of programs from one source language to another which system receives a particular program in the initial source language and makes multi-passes through the initial source code and generates those particular declarations, procedures and routines in an appropriate order and according to the particular pass being made so that at the end of the translation routine, the program received in an initial source language will have been translated into a second source language.

A particular feature of the present invention resides in the above described multi-pass translation system wherein during one of the passes, the structure of the program in its initial source language is created in the second source language so as to allow the program as created in the second source language to accurately reflect the same procedures and routines as were called for in the initial source language.

The above and other objects, advantages, and features of the present invention will become more readily apparent from a review of the following specification when taken in conjunction with the drawings wherein:

FIG. 1 is a diagram illustrating the relation between the various types of source language statements of RPG and the corresponding COBOL Divisions and Sections;

FIG. 2 is a schematic diagram of a general purpose data processing system in which the present invention may be embodied;

FIG. 3 is a flow diagram illustrating the routine of the initial pass performed by the system of the present invention for checking syntax of the initial source code;

FIG. 4 is a flow diagram illustrating the routines of the remaining passes performed by the system of the present invention;

FIG. 5 is a flow diagram illustrating a routine of the second pass performed by the present invention;

FIG. 6 is a flow diagram illustrating the routine of the third pass performed by the system of the present invention;

FIG. 7 is a flow diagram illustrating the routine performed by the last pass performed by the system of the present invention; and

FIG. 8 is a flow diagram illustrating the routine which forms the basic structure of a program in the RPG source language.

The difficulties which arise in the translation from a program in one higher level language to a program in another higher level language are principally due to the differences in the respective language structures and formats. Therefore, the difficulties may be minimized by comparing the basic structure of the program in the respective languages and converting to the second language at those entries where the structures or substructures most readily compare and then repeating the process until complete translation has been achieved.

More specifically, the system of the present invention employs a general and flexible COBOL overstructure that can satisfy the requirements of the entire RPG source language and the system operates to make a number of sequentially passes over a particular program in RPG source language to emit whatever COBOL code is permitted during that pass. The first pass is employed to check the syntax of the RPG source program and to generate tables as required. The remaining passes are employed to generate the COBOL source file and more specifically operate to sequentially declare all data fields, emit COBOL statements to accomplish "moves" required by the RPG cycle and then to generate the COBOL source language routines as required. Thus, the RPG source statements are actually read through four times, with each of the four passes doing its part in constructing the COBOL program.

In the multi-pass design of the present system, one pass can declare a COBOL variable by name and, much later, another pass can reference it. This multi-pass translation then allows for a more accurate interpretation of the true intent of the RPG source program.

Before describing the system and the methods of the present invention, the respective program structures of the RPG source program and the desired COBOL source program will first be described in reference to FIG. 1. As illustrated therein, the RPG source language statements fall into five groups represented by the first column of statements. The remaining three columns in FIG. 1 represent the respective COBOL divisions including the section names within the procedure division which divisions and sections are associated with the RPG source statement classifications in their corresponding row. The separate classifications will now be reviewed to see what COBOL code is to be generated for the statements coded in RPG form.

The RPG File statements are really file description specifications or specifications of the files to be employed by the program. These statements or specifications probably develop more code then any of the other source statements. These specifications generate the file-control assignments and also the necessary code for the file description specifications of the Data division of the resultant COBOL program. In the file description specification format, a rather simple one line statement in RPG code will generate the code for the file handling procedures which include the indicating of the end of input, matching records between files, checking records sequence, as well as the opening and closing of files. As an example, four lines of RPG code can generate some 138 lines of COBOL code, since, with a fixed format language like that of RPG, one or two statements can specify a COBOL procedure. As indicated in FIG. 1, the corresponding COBOL entries to be generated include the Identification division of the resultant COBOL program which consists of only a few lines to identify the program and so on; the Environment division of the resultant COBOL program which specifies the computers to be used, the storage size, the number of tape units and other input and output equipment and the like; and the Data division of the resultant COBOL program which specifies the files, records, and other data items that are to be processed or produced as results. As further indicated in FIG. 1, such RPG file statements also generate code for the initialization of the RPG cycle procedure, the input-read procedure and the open-close file procedure.

The second classification of RPG source language statements as illustrated in FIG. 1 are the File Extension statements which are literally an extension of the above described file statements, when required, such as when two disk files are chained together, i.e., where a field of one file record is used as a key for the accessing of a record in another file. Such File Extension statements also allow the programmer to specify tables within his program and whether they can be loaded at an object time or if the table content is available at compile time and therefore imbedded with the COBOL code.

The third classification of RPG source language statements are the Input statements which specify, for the resulting COBOL source program, the input record descriptions including the size of the item, its usage, the class of the item and its value where required. The input statements also specify the input-move procedure and input-check procedure.

The Calculation statements from the fourth classification of RPG source statements and are to be mapped into calculation procedures for the resulting COBOL program.

The last classification of RPG statements are the Output statements from which the output record descriptions are to be generated as well as the respective output procedures.

Further information on RPG may be found in R. W. Brightman and J. R. Clark, RPG I and RPG II Programming, Macmillan Company (1970) and Report Program Generator Reference Manual, IBM System Reference Library No. GC 24-9001. For additional information on COBOL, reference is made to D. D. McCracken, A Guide to COBOL Programming, John Wiley & Sons, Inc. (1963) and B2500/B3500/B4500 COBOL Reference Manual, Burroughs Corporation.

Referring now to FIG. 2, there is shown therein a representation of a general purpose data processing system in which the present invention is to be employed. This system may employ one or more central processor modules 10 to perform the various data manipulation and moves as may be required by particular programs; one or more memory modules 11 to store data and other information as may be immediately required by the processor and a plurality of peripheral devices including one or more disk files 13, card readers 14, magnetic tape units 15, and data line communication controllers 16 from which data may be transferred to memory modules 11 or to central processor module 10 by way of the input-out module 12. A more detailed description of such a system may be found, for example, in Lynch et al, U.S. Pat. No. 3,411,139 and Anderson et al U.S. Pat. No. 3,419,849. A particular processing module of the type that may be employed is disclosed in Barnes et al, U.S. Pat. No. 3,401,376.

The relation between the RPG source structure and the corresponding COBOL divisions into which RPG structure is to be mapped having been described generally, the methods or algorithms by which this mapping or conversion is accomplished will now be described in relation to FIGS. 3 and 4. As was indicated generally above, the method of the present invention is that of sequential multi-passes, the first of which checks the syntax of the RPG program to ascertain tht the syntax contains no error that might be translated into the resultant COBOL source program. As indicated in FIG. 3, this first pass includes the steps of reading the source program card and analyzing those columns which specify the particular identity. If the card is unidentified or contains a comment, a comment statement is set up and written into a disk file and the routine then reads the next source program card. Should the card contain a specific card type identification, this type is determined and its data fields are analyzed to see if they are applicable to that card type. The data is stored in an appropriate table and a syntax and cross reference of the data is performed. If there is no syntax error, the source card is printed and the routine examines the next source program card until the end of the file is reached at which time the resultant disk file and tables are passed to the program generator.

After the first pass over the RPG source program to check syntax and create data tables, three more passes through the RPG source program are made each of which passes result in the emmission of generated COBOL code. The second pass reads the intermediate files and generates COBOL data declarations and also builds tables and switches for later passes. The emitted code is stored on an intermediate disk file. During the third pass, executable instructions in COBOL code for a first part of COBOL procedures are generated from a first half of the RPG source and the code thus generated is stored in the COBOL source language file. During the fourth pass, the COBOL source language routines are generated by reading or examining all the entries in the intermediate RPG source file created during the second pass of the routine.

The second pass of the routine declared all data fields, the third pass was a partial pass of the input specification and generated the RPG cycle and also emitted COBOL statements to accomplish "moves" and the last pass of the routine generated the COBOL statements required to open and close declared fields and perform the calculation procedures.

The COBOL source language thus created may then be supplied to the COBOL compiler, for the particular processor being employed, for compilation into the machine language of that processor.

As has been indicated above, the system of the present invention achieves translation of a program from the RPG source language into the COBOL source language by making four passes through the RPG source language code. On the first pass, the system of the present invention checks for error in syntax of the RPG code and also sets up those tables that will be later required during the translation itself. The method or algorithm of this first pass has been generally described above and examples of the tables so set up will be given below. For the sake of consistency, this first pass will be called pass No. 0 and the remaining three passes which comprise the COBOL generator program will be referred to then as passes Nos. 1, 2, and 3.

The next three passes employed by the system of the present invention generate the desired COBOL source code and these three passes will now be described in reference to the flow diagrams of FIG. 5, 6, and 7. As indicated in FIG. 5, the intermediate RPG source language files and RPG field files indicator names were obtained from the first pass of the system which also checked the RPG syntax and pass No. 1 effects the beginning of the creation of the output COBOL source language file and generates the COBOL Identification Division (which was described above). During this pass, the file declarations are generated, and the RPG fields are declared. The system then proceeds to describe the output records to be generated, to declare holding areas and program switches and, at the end of the COBOL declarations, to close the RPG source file. The system then exits from pass No. 1 and enters the routine for pass No. 2.

The routine of pass No. 2 of the COBOL generator program is illustrated in the diagram of FIG. 6. As indicated therein, pass No. 2 is effective to again open the RPG source language files and to begin the creation of the COBOL Procedure Division (which was generally described above). This routine then operates to generate the RPG cycle code (which will be more thoroughly described below), to generate "input-move" COBOL code from the RPG input specifications and to build cross reference tables for use during pass No. 3. This routine then closes the RPG source files and the system exits from pass No. 2.

The third and final pass of the COBOL generator program is illustrated in FIG. 7. As shown therein this third routine again opens the RPG source file and proceeds to generate the "open-close files" COBOL routine from the RPG file specifications. to generate the "input-check" COBOL routine from the RPG input specifications, to generate the "calculation" COBOL routine from the RPG calculation specifications and to generate the "output" COBOL routines from the RPG output specifications. The respective files are then closed and the routine of pass No. 3 is then ready to exit to a COBOL compiler.

At this point, the program that was originated in the RPG source language has now been translated to the COBOL source language and can now be compiled into the object code or machine language of the data processing system in which the program is desired to be run.

As was indicated above in the description of pass No. 2 (See FIG. 6) this pass generates the COBOL code for the "RPG cycle" which cycle is the general structure of any program as it exists in the RPG source language. This cycle is illustrated in FIG. 8 and will now be described with reference thereto.

At the beginning of the RPG cycle, a heading and detail output is performed and checks are made of overflow, halt, and other identifying indicators. The routine begins to read one record from each file. If the record type sequence is incorrect, the routine is halted and a read from the next record is initiated. If the record just read is the last record, a check is made to see if multi-file processing is required and, if not, the calculation routine is entered which will be described below. If the record is not the last record or if the last card of the last appropriate file has not been processed, then a check is made to see if multiple input files are defined which may require the determination of the priority of respective multiple input files, a check is made of correct sequence if matching fields are specified, the record identifying indicator and the appropriate control level indicators are set and the calculation routine is then entered.

If the record just read is the last record in the file, the calculations conditioned by the control level indicators are performed and a total output is effected. If the record was the last record to have been read, this then completes the program job. If the record that was read is not the last record, an overflow check is made, the respective field indicators are set and data is made available from the last card selected. All calculations not conditioned by control level indicators are now performed and the resulting indicators are set. The RPG program cycle now has been completed and this cycle is re-entered and repeated until the end of the program job.

In order to provide a better understanding of the present invention, a test program will now be presented, first in the RPG source language and then as converted to the COBOL source language. This program is merely a test program including of "move", "add" and "go to" RPG statements.

The test program in RPG is as follows: ##SPC1## ##SPC2##

As was explained above, the RPG program is read through four times by the system of the present invention. During the initial pass through the above RPG program, that program will be printed out if it is free of RPG syntax error and also, during the initial pass, the tables required by the translation will be defined or established as listed below. ##SPC3##

During the second pass through the above RPG program, the system of the present invention generates the file declarations, descriptions of input records and declares the RPG fields. The results of this second pass are printed out as follows (the remaining print-outs are in COBOL): ##SPC4## ##SPC5##

During the third pass (pass No. 2) through the above described RPG program, the system of the present invention creates the COBOL Procedure division for the program and the RPG cycle code and cross-reference tables. The results of this third pass (pass No. 2) are printed out in COBOL as follows: ##SPC6## ##SPC7##

During the fourth and final pass (pass No. 3)through the above described RPG program, the system of the present invention generates the remaining required COBOL routines. The results of this final pass (pass No. 3) are printed out in COBOL as follows: ##SPC8## ##SPC9##

The system thus described is a multi-pass system for translation of a program from one source language to another. In this manner statements for which there is a one for one correspondence may be translated during one pass. Yet statements which require more than one pass through the input source code are also accommodated. For example, the numerous "move" statements which appear in the above example require that the data fields and files, between which the moves are to be accomplished, first be declared or defined. In a single pass translation system, move statements are not assured of accurate translation. Another example of an RPG statement that would not be accommodated by a single pass system is that of "sequence checking" since the sequence in question must first be established in an intermediate file (in this case during pass No. 2) before the criteria for the sequence check can be specified.

The system and method by which the present invention accomplishes source to source code translation having been described, there will now be given a description of the manner in which the translation system is embodied in a data processing system to form an information processing system to accomplish such translation. As was described in relation to FIG. 2, such a data processing system would include a central processing module 10, memory modules 11, as well as peripheral devices such as a disk file 13, card reader 14, and the like. Memory modules 11 may be of any standard memory units normally employed as main memory for a data processing system such as core storage, integrated circuit memories and the like. The program listings which form the translation system may be entered into memory modules 11, for example, from a card deck by way of card reader 14. The entire program listings may be resident in memory modules 11 or, if desired in order to save core storage space, only the listings required for particular passes of the translation may be stored therein in sequence. Once the program listings are resident in main memory, a program to be translated from RPG to COBOL is then supplied to the data processing system, again by way of card reader 14, for example. During the first pass of the translation system, the RPG program source code will be checked for syntax as was described above and the data tables definitions called for thereby are transferred from the card deck to main memory. During the first pass of the translation, the error free RPG program code is transferred along with the table definitions to an intermediate file, preferably in disk file 13. At this point, the program listing to effect the first pass or pass No. 0 may then be dumped from main memory in order to provide more memory space.

The intermediate RPG files have now been created in disk file 13 and the program listings for the COBOL generator may now be entered into main memory if they were not already resident there. During the respective passes Nos. 1-3 of the COBOL generator, the COBOL source language file is created in the disk file 13. At the end of the translation, this COBOL source file may then be read out from disk file 13, for example to magnetic tape unit 15, or may be compiled into the machine language listings of the data processing system in which they are now resident should that data processor be provided with a COBOL compiler routine.

In order to provide a more complete disclosure, there are provided below six appendices which are print-outs of the five sections of the system of the present invention to effect the four passes through the RPG source code to convert that code into COBOL. The sixth appendice is a print-out of the routines called for by statements in the other sections to effect the conversion. In order to provide proper correlation between the respective appendices and the respective passes employed by the system of the present invention as identified above, the appendices will now be identified:

Appendix A: Pass No. 0 (initial pass) for syntax check and table generation.

Appendix B: Data declarations for passes Nos. 1-3.

Appendix C: Pass No. 1 to declare files and RPG fields and describe input records.

Appendix D: Pass No. 2 to create COBOL procedures and to generate the RPG cycle code.

Appendix E: Pass No. 3 to generate remaining COBOL routines.

Appendix F: Routines to be called by Passes 1-3.

The above appendices represent the complete system of the present invention except that the definitions of the working storage have been left out of Appendices A and B since such definitions are not necessary to an understanding of the present invention. All of the respective appendices are printed out in B2500/B3500/B4500 COBOL.

A system and method have been disclosed for the automatic translation of programs from the RPG source language to the COBOL source language. This system and method produce an accurate translation even though the substance and format of various statements and procedures differ in their respective languages. The value of the RPG source language is its simplicity and compactness which allow very simple programs to be written in a relatively few number of statements. Conversely, the disadvantage of the RPG language is its inability to accommodate more complex business oriented programs the latter of which can be accommodated by COBOL. Furthermore, while the user may find the RPG language to be advantageous for use in small data processing systems, he must be provided with some conversion technique if he is to change to a larger data processing system which is provided with a COBOL compiler but not with an RPG compiler.

With the system and method of the present invention, the user receives all the benefits of the more generalized COBOL compiler for use in a larger data processor and yet may continue to write simple programs in the RPG language where appropriate. Furthermore, the system and method of the present invention allows the user to convert from a smaller data processing system to a larger data processing system without having to rewrite his RPG programs. The system and method of the present invention provide for accurate translation even though the various "move" and "edit" statements and the like differ in form and substance in the respective languages which differences may be detected from a comparison of the test program illustrated above in both languages.

While but one particular embodiment of the present invention has been disclosed, it will be apparent to those skilled in the art that variations and modifications may be made therein without departing from the spirit and the scope of the invention as claimed. ##SPC10## ##SPC11## ##SPC12## ##SPC13## ##SPC14## ##SPC15## ##SPC16## ##SPC17## ##SPC18## ##SPC19## ##SPC20## ##SPC21## ##SPC22## ##SPC23## ##SPC24## ##SPC25## ##SPC26## ##SPC27## ##SPC28## ##SPC29## ##SPC30##