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Defensive Publications Series

12 Nov 2020

Replacement of Goto Statements During Code Migration Replacement of Goto Statements During Code Migration

Paneendra BA

Paul McReynolds

Abhay Garg

Arijit De

Alex Ginet

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Replacement of Goto Statements During Code Migration

ABSTRACT

This disclosure describes code conversion techniques for replacement of Goto statements

in program code in a source language with equivalent constructs in a target language. Different

types of equivalent code constructs are utilized to replace Goto statements in the source

language, depending on the use of the Goto statement in the original code that is to be converted.

Another option is to introduce a method-like syntax in the language. Backward jumps and

● JavaScript

● Goto statement

● Code migration

● Legacy code

● Recursion

BACKGROUND

During migration of legacy computer applications, code written in a particular

programming language may have to be converted (translated) into code in a different

programming language. Automatic tools are available for such code migration and can

efficiently convert code from one language to another.

Some source programming languages support the use of Goto statements/keywords. Goto

statements. Translation of Goto statements using standard constructs such as loops and closures

that are provided in most programming languages can enable automatic migration of code that

includes Goto statements.

DESCRIPTION

This disclosure describes techniques for automatic replacement of Goto statements in

program code with equivalent constructs. The techniques can be utilized, for example, during

migration of code from one programming language that supports Goto statements to another

programming language that does not support Goto statements. An automated tool can implement

the described techniques to convert code written in a particular language that supports a Goto

statement, e.g., Basic, Visual Basic, etc. to a different programming language that may not

declarations are included at a top-level in a corresponding function, etc. If the conditions are not

met and it is determined that the file is not convertible, a suitable message (e.g., “File not

supported”) is provided to the user that attempts code conversion.

Different types of equivalent constructs are utilized to replace Goto statements,

depending on the use of the Goto statement in the original code that is to be converted.

Support for Goto statements can be added to a parser associated with a language to

explicitly recognize Goto as a keyword. Another option is to introduce a method-like syntax in a

language, e.g., Goto(label) which obviates the need for any parsing change, while providing

A backward jump refers to a Goto statement in code where the label appears before the

Goto statement. Conversion of instances of a backward jump is handled by the addition of a new

do-while loop starting from a label associated with the Goto statement that extends till the end of

a current block.

Fig. 2: Backward jump Goto statement; (a) original code; (b) equivalent code

Fig. 2 depicts an example of code conversion that includes a Goto statement that

implements a backward jump. Fig. 2(a) depicts code in an original programming language, while

Fig. 2(b) depicts equivalent translated code.

Forward jump is when the Goto statement appears before the label in the method. A

Fig. 3(b) depicts equivalent translated code.

Some sections of complex code may include placement of Goto statements that cannot be

converted using do-while loops. In such situations, closure may be utilized to replace Goto

keywords. Code blocks are divided into closure methods and chained up such that at the end of a

block, a function representing the next block is called. This enables entry into any code block by

Fig. 4 depicts an example of utilization of closure methods for replacement of Goto

statements during code conversion. Fig. 4(a) depicts code in an original programming language,

while Fig. 4(b) depicts equivalent translated code.

commonly followed by a "Goto label", "Goto 0”, etc. This statement specifies action(s) to be

for errors while it is being executed, while a catch statement enables definition of a block of code

to be executed, upon encountering an error in the try block.

For conversion of code that includes On Error Goto statements, a block of statements of

corresponding block of statements is included as consequent statements within the if block.

Fig. 5 depicts an example of handling of On Error Goto statements during code

conversion. Fig. 5(a) depicts code in an original programming language that utilizes On Error

statements, while Fig. 5(b) depicts equivalent translated code that utilizes try-catch blocks.

CONCLUSION

This disclosure describes code conversion techniques for replacement of Goto statements

in program code in a source language with equivalent constructs in a target language. Different