Editing RPL (programming language) (section)

====IFT/IFTE====
Postfix conditional testing may be accomplished by using the IFT ("if-then") and IFTE ("if-then-else") functions.

IFT and IFTE pop two or three commands off the stack, respectively. The topmost value is evaluated as a Boolean and, if true, the second topmost value is pushed back on the stack.  IFTE allows a third "else" value that will be pushed back on the stack if the Boolean is false.

The following example uses the IFT function to pop an object from the bottom of the stack and, if it is equal to 1, replaces it with "One":

  « 1 == "One" IFT »

The following example uses the IFTE function to pop an object from the bottom of the stack and, if it is equal to 1, replaces it with "One". If it does not equal 1, it replaces it with the string "Not one":

  « 1 == "One" "Not one" IFTE »

IFT and IFTE will evaluate a program block given as one of its arguments, allowing a more compact form of conditional logic than an IF/THEN/ELSE/END structure. The following example pops an object from the bottom of the stack, and replaces it with "One", "Less", or "More", depending on whether it is equal to, less than, or greater than 1.

  «
    DUP 1 ==
    « DROP "One" »
    « 1 < "Less" "More" IFTE »
    IFTE
  »