Editing RPL (programming language) (section)

===Looping statements===

====FOR/NEXT====
RPL provides a FOR/NEXT statement for looping from one index to another. The index for the loop is stored in a temporary local variable that can be accessed in the loop. The syntax of the FOR/NEXT block is:

 index_from index_to FOR variable_name loop_statement NEXT

The following example uses the FOR loop to sum the numbers from 1 to 10. The index variable of the FOR loop is "I":

  « 
     0       @ Start with zero on the stack
     1 10    @ Loop from 1 to 10
     FOR I   @ "I" is the local variable
        I +  @ Add "I" to the running total
     NEXT    @ Repeat...
  »

====START/NEXT====
The START/NEXT block is used for a simple block that runs from a start index to an end index.  Unlike the FOR/NEXT loop, the looping variable is not available. The syntax of the START/NEXT block is:

  index_from index_to START loop_statement NEXT

====FOR/STEP and START/STEP====
Both FOR/NEXT and START/NEXT support a user-defined step increment. By replacing the terminating NEXT keyword with an increment and the STEP keyword, the loop variable will be incremented or decremented by a different value than the default of +1. For instance, the following loop steps back from 10 to 2 by decrementing the loop index by 2:

  « 10 2 START -2 STEP »

====WHILE/REPEAT/END====
The WHILE/REPEAT/END block in RPL supports an indefinite loop with the condition test at the start of the loop. The syntax of the WHILE/REPEAT/END block is:

  WHILE condition REPEAT loop_statement END

====DO/UNTIL/END====
The DO/UNTIL/END block in RPL supports an indefinite loop with the condition test at the end of the loop. The syntax of the DO/UNTIL/END block is:

  DO loop_statement UNTIL condition END