Reference Guide

2-28 RPL Programming Examples
Techniques used in →RPN
 Recursion. The →RPN program calls itself as a subroutine. This powerful technique works just like calling
another subroutine as long as the stack contains the proper arguments before the program calls itself. In this case
the level 1 argument is tested first to be sure that it is an algebraic expression before →RPN is called again.
 Object Type-Checking. →RPN uses conditional branching that depends on the object type of the level 1
object.
 Nested program Structures. →RPN nests IF…THEN…END structures inside FOR…NEXT loops inside a
IF…THEN… ELSE…END structure.
 List Concatenation. The result list of objects in RPN order is built by using the ability of the + command to
sequentially append additional elements to a list. This is a handy technique for gathering results from a looping
procedure.
→RPN program listing
Program: Comments:
«
OBJ→
IF OVER
THEN → n f
Take the expression apart.
If the argument count is nonzero, then
store the count and the function.
«
Begins local variable defining procedure.
1 n
FOR i
Begins FOR…NEXT loop, which
converts any algebraic arguments to lists.
IF DUP TYPE 9. SAME
Tests whether argument is an algebraic.
THEN →RPN
If argument is an algebraic, convert it to a
list first.
END n ROLLD
Roll down the stack to prepare for the
next argument.
NEXT
Repeat the loop for the next argument.
IF DUP TYPE 5. ‹
Tests to see if level 1 object is a list.
THEN 1 →LIST
If not a list, then convert it to one.
END
Ends the IF…THEN…END structure.
IF n 1 >
Tests to see if there is more than one
argument.
THEN 2 n
START +
NEXT
Combine all of the arguments into a list.
END f +
Append the function to the end of the list.
»
End the local variable defining procedure.
ELSE 1 →LIST SWAP DROP
For functions with no arguments,
converts to a simple list.
END
End the IF…THEN… ELSE…END
structure.
»
`O →RPN K
Stores the program in →RPN.