4.8 Top Down and Structured Programming Techniques
This guideline is very simple, yet it will allow LANSA programs to be completed more quickly and accurately.
When working on the code of a specific RDML function, always attempt to use a "top down" approach to coding. For instance, you may be given a program "specification" which looks like this:
- Repeat until program terminated at user request
- Get the user to input an order number
- Get details of the order, and handle record not found
- Get details of all the order lines
- Display the order details and the line details
You must now "translate" this specification into the LANSA rapid development language.
With a structured (or organized) approach to coding, the program will follow similar steps to the example below.
Note how the arrow --> is used to indicate the new lines inserted in each step:
Step 1
--> ********** Do until terminated by EXIT or MENU key
--> BEGIN_LOOP
--> END_LOOP
Step 2
********** Do until terminated by EXIT or MENU key
BEGIN_LOOP
--> ********** Request order number input until order is found
--> ********** Build a list of all order lines
--> ********** Display the order and its lines to the user
END_LOOP
Step 3
********** Do until terminated by EXIT or MENU key
BEGIN_LOOP
********** Request order number until order is found
--> DOUNTIL COND('#IO$STS = OK')
--> ENDUNTIL
********** Build a list of all order lines
********** Display the order and its lines to the user
END_LOOP
Step 4
********** Do until terminated by EXIT or MENU key
BEGIN_LOOP
********** Request order number until order is found
DOUNTIL COND('#IO$STS = OK')
ENDUNTIL
********** Build a list of all order lines
--> CLR_LIST NAMED(#LINES)
--> SELECT FIELDS(#LINES) FROM_FILE(ORDLIN) WITH_KEY(#ORDNUM)
--> ENDSELECT
********** Display the order and its lines to the user
END_LOOP
Step 5
********** Do until terminated by EXIT or MENU key
BEGIN_LOOP
********** Request order number until order is found
DOUNTIL COND('#IO$STS = OK')
ENDUNTIL
********** Build a list of all order lines
CLR_LIST NAMED(#LINES)
SELECT FIELDS(#LINES) FROM_FILE(ORDLIN) WITH_KEY(#ORDNUM)
ENDSELECT
********** Display the order and its lines to the user
--> DISPLAY FIELDS(#HEADER) BROWSELIST(#LINES)
END_LOOP
Step 6
********** Do until terminated by EXIT or MENU key
BEGIN_LOOP
********** Request order number until order is found
DOUNTIL COND('#IO$STS = OK')
--> ********** Request user inputs an order number
--> ********** Attempt to locate the order
--> ********** Issue message if order was not found
ENDUNTIL
********** Build a list of all order lines
CLR_LIST NAMED(#LINES)
SELECT FIELDS(#LINES) FROM_FILE(ORDLIN) WITH_KEY(#ORDNUM)
ENDSELECT
********** Display the order and its lines to the user
DISPLAY FIELDS(#HEADER) BROWSELIST(#LINES)
END_LOOP
Step 7
********** Do until terminated by EXIT or MENU key
BEGIN_LOOP
********** Request order number until order is found
DOUNTIL COND('#IO$STS = OK')
********** Request user inputs an order number
REQUEST FIELDS(#ORDNUM)
********** Attempt to locate the order
--> FETCH FIELDS(#HEAD) FROM_FILE(ORDMST) WITH_KEY(#ORDNUM)
********** Issue message if order was not found
ENDUNTIL
********** Build a list of all order lines
CLR_LIST NAMED(#LINES)
SELECT FIELDS(#LINES) FROM_FILE(ORDLIN) WITH_KEY(#ORDNUM)
ENDSELECT
********** Display the order and its lines to the user
DISPLAY FIELDS(#HEADER) BROWSELIST(#LINES)
END_LOOP
Step 8
********** Do until terminated by EXIT or MENU key
BEGIN_LOOP
********** Request order number until order is found
DOUNTIL COND('#IO$STS = OK')
********** Request user inputs an order number
REQUEST FIELDS(#ORDNUM)
********** Attempt to locate the order
FETCH FIELDS(#HEAD) FROM_FILE(ORDMST) WITH_KEY(#ORDNUM)
********** Issue message if order was not found
--> IF_STATUS WAS_NOT(*OKAY)
--> ENDIF
ENDUNTIL
********** Build a list of all order lines
CLR_LIST NAMED(#LINES)
SELECT FIELDS(#LINES) FROM_FILE(ORDLIN) WITH_KEY(#ORDNUM)
ENDSELECT
********** Display the order and its lines to the user
DISPLAY FIELDS(#HEADER) BROWSELIST(#LINES)
END_LOOP
Step 9
********** Do until terminated by EXIT or MENU key
BEGIN_LOOP
********** Request order number until order is found
DOUNTIL COND('#IO$STS = OK')
********** Request user inputs an order number
REQUEST FIELDS(#ORDNUM)
********** Attempt to locate the order
FETCH FIELDS(#HEAD) FROM_FILE(ORDMST) WITH_KEY(#ORDNUM)
********** Issue message if order was not found
IF_STATUS WAS_NOT(*OKAY)
--> MESSAGE MSGTXT('No details of this order found')
ENDIF
ENDUNTIL
********** Build a list of all order lines
CLR_LIST NAMED(#LINES)
SELECT FIELDS(#LINES) FROM_FILE(ORDLIN) WITH_KEY(#ORDNUM)
ENDSELECT
********** Display the order and its lines to the user
DISPLAY FIELDS(#HEADER) BROWSELIST(#LINES)
END_LOOP
Step 10
********** Do until terminated by EXIT or MENU key
BEGIN_LOOP
********** Request order number until order is found
DOUNTIL COND('#IO$STS = OK')
********** Request user inputs an order number
REQUEST FIELDS(#ORDNUM)
********** Attempt to locate the order
FETCH FIELDS(#HEAD) FROM_FILE(ORDMST) WITH_KEY(#ORDNUM)
********** Issue message if order was not found
IF_STATUS WAS_NOT(*OKAY)
MESSAGE MSGTXT('No details of this order found')
ENDIF
ENDUNTIL
********** Build a list of all order lines
CLR_LIST NAMED(#LINES)
SELECT FIELDS(#LINES) FROM_FILE(ORDLIN) WITH_KEY(#ORDNUM)
--> ADD_ENTRY TO_LIST(#LINES)
ENDSELECT
********** Display the order and its lines to the user
DISPLAY FIELDS(#HEADER) BROWSELIST(#LINES)
END_LOOP
You should find that well structured and documented programs are very easy to produce by using this type of approach, which basically consists of always:
- entering the structured programming constructs completely before coming back to fill in the details.
For example: BEGIN_LOOP/END_LOOP, DOUNTIL/ENDUNTIL, SELECT/ENDSELECT, IF/ELSE/END, etc. etc.
- including the comments before the commands.