RPN ( expression )

[Ocean West]

Name & Parameters: [color:red][big] RPN ( expression ) [/big]

Description: This CF will allow you to evaluate an expression with Rerverse Polish Notation.

where entry detrmines order of operation, using a stack to push and pull from.

RPN input would be written 10 25 2 * + 40 +

Infix input would be written : ((25 * 2) + 10) + 40

For more info: http://en.wikipedia.org/wiki/Reverse_Polish_notation

Sample Input:

10 25 2 * + 40 +

Results:

100

Recursive: yes

Formula:

// RPN( expression )  or Reverse Polish Notation 

// by Stephen Dolenski 



Let ([

exp = Substitute( expression ; " " ; ¶) ; // pivot expression into a return sep list.

exp_len = ValueCount ( exp ) // count entries.

];





//============================



If(  $i   >   exp_len ;   



Let( $i = 1 ; $stack)

;





If(  Filter( GetValue(exp ; $i) ; "*+-/")  ≠ $null ;   // value is operator



     Let ([

          $result =  Evaluate(GetValue ($stack ; 1 )  &  GetValue(exp ; $i)  & GetValue ($stack ; 2 ))  ;

          $stack =  Substitute( $stack ; [GetValue ( $stack; 1 )  & "¶" & GetValue ( $stack; 2 )  & "¶"  ; $result &¶] ; [GetValue ( $stack; 1 )  & "¶" & GetValue ( $stack; 2 ) ; $result]);

          $i = $i+1

          ]; 

          RPN( exp ) 

          ) // end let



     ; // else append stack



        Let ([ 

        $stack = Case( $i = 1; GetValue (exp ; 1 ) ; GetValue(exp ; $i) & ¶& $stack );

        $i = $i+1

        ]; RPN( exp )

        ) // end let

     ) // end if



) // end if





//============================



) // close let

 

Required Functions:

Author(s): Ocean West

Date: 03/28/06

Credits:

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RPN.fp7.zip