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EDT:Writing statements

Revision as of 18:29, 13 February 2012 by Margolis.us.ibm.com (Talk | contribs)

EGL provides two kinds of statements:

  • General statements such as if and while, for processing the data that is immediately available to your logic.
  • Action statements such as add and call, for accessing external data sources or invoking external logic.

General statements

The general statements are case, continue, exit, for, if, return, throw, try, use, and while.

Case

The case statement responds to conditions at run time by executing one set of statements rather than another:

  • You can test a criterion value. The following example invokes mySecondFunction:
function test()
   x Int = 3; 
 
   case (x)
      when (1)
         myFirstFunction();
      when (2, 3, 4)
         mySecondFunction();      
      otherwise
         myDefaultFunction();
   end   
end
  • You can test a set of logical expressions. The following example displays only "x passes":
function test()
   x Int = 3;
   y Int = 5;
   z Int = 7;
 
   case
      when (x == 3)
         SysLib.writeStdOut("x passes");
      when (y == 5)
         SysLib.writeStdOut("y passes");
      when (z == 7)
         SysLib.writeStdOut("z passes");
      otherwise
         SysLib.writeStdErr("You will not see this message.");
      end
   end 
end

As shown, no more than one clause ever executes. Control does not “fall through” from one clause to the next.


Continue

The continue statement returns control to the start of a block of code controlled by a for, forEach, or while statement. The statement lets you return to a labeled statement of one of those kinds, or to the nearest embedding statement of one of those kinds.

Here is an example:

inputList int[] =[2, 4, 6, 8, 10, 12, 14, 16];
 
for(i int from 1 to inputList.getSize() by 1)
   SysLib.writeStdOut(inputList[i]);
 
   if((i % 3) != 0)
      continue;
   end // if
 
   SysLIb.writeStdOut(" ");
end

The code displays each integer on its own line, inserting a blank line after each group of three.

Exit

The exit statement exits from a function, program, service, or run unit; or from a block of code controlled by a case, for, forEach, if, or while statement.

For

The for statement runs a set of statements in a loop that repeats until a counter exceeds a specified value.

The example code shows three variations of a for statement that adds the same set of numbers.

program MyTestProgram
 
   function main()
      inputList int[] =[10, 4, 6, 8, 2];
      numberInList int = inputList.getSize();
      sum = 0;
 
      // the first for loop increments by 1.
      for(i int from 1 to numberInList)
         sum = inputList[i] + sum;
      end
 
      SysLib.writeStdOut("sum after the first for loop is " + sum);
      sum = 0;
 
      // the second for loop has the same effect but specifies the increment value. 
      for(i int from 1 to numberInList by 1)
         sum = inputList[i] + sum;
      end
 
      SysLib.writeStdOut("sum after the second for loop is " + sum);
      sum = 0;
 
      // the third for loop starts at the opposite side of the list and decrements by 1
      for(i int from numberInList to 1 decrement by 1)
         sum = inputList[i] + sum;
      end
 
      SysLib.writeStdOut("sum after the third for loop is " + sum);
   end
end

In each case, the variable i was local to the for statement. Here is an alternative:

i int;
 
for(i from 1 to numberInList)
   sum = inputList[i] + sum;
end

After that code ends, the value of i is available and equals numberInList + 1

If

The if statement runs a set of statements if a logical expression resolves to true. The optional else keyword marks the start of an alternative set of statements that run only if the logical expression resolves to false.

The following code shows how to embed If statements in other If statements.  

program MyTestProgram
 
   // A binary search finds a value in a sorted (preferably short) list.
   function binarySearch(list int[], lowIndex int, highIndex int, value int) returns(int)
 
      while(true)
         middleIndex int = (lowIndex + highIndex) / 2;
 
         if(list[middleIndex] == value)
            return(middleIndex);
         else
            if(list[middleIndex] >= value)
               highIndex = middleIndex - 1;
            else
               if(list[middleIndex] < value)
                  lowIndex = middleIndex + 1;
               end
            end
         end
 
         if(highIndex < lowIndex)
            return(-1);
         end
      end
   end
 
 
   function main()
 
      myNumbers int[] =[-6, -1, 2, 4, 7, 9 ];
      valueOfInterest int = -1;
 
      lowestIndex int = 1;
      highestIndex int = myNumbers.getSize();
 
      location int = binarySearch(myNumbers, lowestIndex, highestIndex, valueOfInterest);
 
      if (location == -1)
         SysLib.writeStdOut("Did not find " + valueOfInterest + ".");
      else
         SysLib.writeStdOut("The value of interest is " + valueOfInterest +
                            ", at location " + location + ".");
      end
   end
end



Return


Throw


Try


Use


While


Action statements

The action statements are add, call, close, delete, execute, forEach, get, open, and prepare.

Except for the call statement, all are now used only for accessing a relational database.


Add

Call

Close

Delete

Execute

ForEach

Get

Open

Prepare

Replace