explaining-legacy-code.md

title	shortTitle	intro	redirect_from	versions	category	complexity	octicon	topics
Explaining legacy code	Explain legacy code	{% data variables.product.prodname_copilot_chat_short %} can help with explaining unfamiliar code.	/copilot/example-prompts-for-github-copilot-chat/documenting-code/explaining-legacy-code	feature copilot	Documenting code	Simple	book	Copilot

One of the biggest challenges with legacy code is helping developers understand it who aren't familiar with the languages or frameworks. With {% data variables.product.prodname_copilot_chat_short %}, you can explain the background you have and ask for an explanation.

Example scenario

Consider the following COBOL code. If you're a Python developer (as an example), you might not be familiar with COBOL, so you could ask {% data variables.product.prodname_copilot_chat_short %} to explain the code to you.

IDENTIFICATION DIVISION.
PROGRAM-ID. INSERT-RECORD.

ENVIRONMENT DIVISION.

DATA DIVISION.
WORKING-STORAGE SECTION.
01  WS-STATUS-FLAGS.
    05 WS-DB-STATUS     PIC X(2).
       88 WS-SUCCESS    VALUE "00".
    05 WS-SQLCODE       PIC S9(9) COMP.
    05 WS-ERROR-MSG     PIC X(50).

LINKAGE SECTION.
01  LS-PARAMETERS.
    05 LS-PERSON-RECORD.
       10 PERSON-ID     PIC 9(6).
       10 PERSON-NAME   PIC X(50).
       10 PERSON-AGE    PIC 9(3).
    05 LS-RESULT        PIC X.
       88 SUCCESS       VALUE 'T'.
       88 FAILED        VALUE 'F'.

PROCEDURE DIVISION USING LS-PARAMETERS.
    PERFORM INSERT-AND-VALIDATE
    GOBACK
    .

INSERT-AND-VALIDATE.
    EXEC SQL
        INSERT INTO persons (id, name, age)
        VALUES (:PERSON-ID, :PERSON-NAME, :PERSON-AGE)
    END-EXEC

    IF SQLCODE = 0
        EXEC SQL COMMIT END-EXEC
        SET SUCCESS TO TRUE
    ELSE
        EXEC SQL ROLLBACK END-EXEC
        SET FAILED TO TRUE
        STRING "DB Error: " SQLCODE
            DELIMITED BY SIZE
            INTO WS-ERROR-MSG
        DISPLAY WS-ERROR-MSG
    END-IF
    .

Example prompt

You can ask for an explanation of the COBOL code from the point of view of a Python developer.

I'm a Python developer. Help me better understand this code. Please provide analogies.

Example response

{% data reusables.copilot.example-prompts.response-is-an-example %}

{% data variables.product.prodname_copilot_short %} provides a high-level overview of the code, before walking through the various operations and explaining them in a way that Python developers can understand. It uses analogies to make the explanation more accessible. The response might start with the following:

Let me explain this COBOL code using Python analogies:

High-Level Overview
This is similar to a Python function that inserts a person's record into a database with error handling.

# In Python, the COBOL divisions would be like:

# IDENTIFICATION DIVISION = module/file name
# PROGRAM-ID = function name
def insert_record():
    pass

# DATA DIVISION would be like declaring these variables:
class WorkingStorage:
    db_status = ""  # WS-DB-STATUS
    sqlcode = 0     # WS-SQLCODE
    error_msg = ""  # WS-ERROR-MSG

# LINKAGE SECTION is like function parameters
class PersonRecord:
    def __init__(self, person_id: int, person_name: str, person_age: int):
        self.person_id = person_id    # PERSON-ID
        self.person_name = person_name # PERSON-NAME
        self.person_age = person_age   # PERSON-AGE
        self.success = False          # LS-RESULT

Further reading

{% data reusables.copilot.example-prompts.further-reading-items %}