Rexx - Performance


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One of the key aspects of any programming language is the performance of the application. Special practices need to be taken care of to ensure that the application’s performance is not hampered. Let’s look at some of the considerations described in steps for better understanding −

Step 1 − Try to reduce the number of instructions – In Rexx each instruction carries an overhead. So try to reduce the number of instructions in your program. An example of instructions that can be redesigned is shown below.

Instead of using multiple if else statements one can use the parse statement. So like in the following program, instead of having an if condition for each value, and getting the value of word1, word2, word3 and word4, use the parse statement.

/* Main program */  

parse value 'This is a Tutorial' with word1 word2 word3 word4 
say "'"word1"'" 
say "'"word2"'" 
say "'"word3"'" 
say "'"word4"'" 

Step 2 − Try to combine multiple statements into one statement. An example is shown below.

Suppose if you had the following code which did the assignment for – a and b and passed it to a method called proc.

do i = 1 to 100 
a = 0 
b = 1 
call proc a,b 
end

You can easily replace the above given code with the following code using the parse statement.

do i = 1 for 100 
parse value 0 1 with 
a, 
b, 
call proc a,b 
end 

Step 3 − Try to replace the do..to loop with the do..for loop wherever possible. This is normally recommended when the control variable is being iterated through a loop.

/* Main program */ 
do i = 1 to 10 
say i 
end 

The above program should be replaced by the following program.

/* Main program */ 
do i = 1 for 10 
say i 
end

Step 4 − If possible, remove the for condition from a do loop as shown in the following program. If the control variable is not required, then just put the end value in the do loop as shown below.

/* Main program */ 
do 10 
say hello 
end

Step 5 − In a select clause, whatever u feel is the best condition which will be evaluated needs to put first in the when clause. So in the following example, if we know that 1 is the most frequent option, we put the when 1 clause as the first clause in the select statement.

/* Main program */ 
select 
when 1 then say'1' 
when 2 then say'2' 
otherwise say '3' 
end 


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