Algebraic to RPN

[compsystems]

userrpl

PHP Code:

« 0 0 { } -> EXPRESSION XPART NPARTS OPERATOR OBJECTS
  « EXPRESSION
    IFERR OBJ->
    THEN ->STR 'OPERATOR' STO 0 'NPARTS' STO OPERATOR 1 ->LIST 'OBJECTS' STO
    ELSE ->STR 'OPERATOR' STO 'NPARTS' STO NPARTS ->LIST 'OBJECTS' STO NPARTS OPERATOR OBJECTS 3 ->LIST DROP
    END
      IF XPART NPARTS <= XPART -1 >= AND NOT
      THEN "EXPRESSION " EXPRESSION + " CONTAINS ONLY " + NPARTS + " PARTS" +
      ELSE
        IF XPART 0 ==
        THEN OPERATOR
        ELSE
          IF XPART -1 ==
          THEN NPARTS
          ELSE OBJECTS XPART GET
          END
        END
      END
  »
»
'PART' STO 


Hi. The code with PART CMD, is simplified to the following, also rename some variables to auto-document the code.

PHP Code:

#pragma mode( separator(.,;) integer(h32) )
#cas
    convToRPN(expr1):=
    begin
      local rpnStr, oper, partn, parts, partJ, expr2;

      rpnStr:="";
      oper:="";
      partn:="";
      if (type(expr1) <> DOM_SYMBOLIC) then
        rpnStr:=string(expr1);
        return(rpnStr);
      end;
      expr1:=(x^2-4*x);
      oper:=string(expr1[1]);  
      parts:=size(oper);  
      oper:=MID(oper,2,parts-2);  
      parts:=dim(expr1) + 1;

      for partJ from 2 to parts do
        expr2:=expr1[partJ];
        if (type(expr2) <> DOM_SYMBOLIC) then
          partn:=string(expr2);
        else
          partn:=convToRPN(expr2);
        end;
        if (partJ > 2) then 
          rpnStr:=rpnStr + " "; 
        end;
        rpnStr:=rpnStr + partn;
        if ((partJ > 2) or (parts == 2)) then
          rpnStr:=rpnStr + " " + oper;
        end;
      end;

      return(rpnStr);
    end;
#end

//(x^2-4*x)[1] -> '+'
//(x^2-4*x)[2] -> x^2
//(x^2-4*x)[3] -> -4*x


#pragma mode( separator(.,;) integer(h32) )
#cas
    convToRPN2(expr1):=
    begin
      local rpnStr, oper, partn, parts, partJ, expr2;
      
      rpnStr:="";
      oper:="";
      partn:="";
      if (type(expr1) <> DOM_SYMBOLIC) then
        rpnStr:=string(expr1);
        return(rpnStr);
      end;
      oper:=part(expr1,0);
      parts:=part(expr1);

      for partJ from 1 to parts do
        expr2:=part(expr1,partJ);
        if (type(expr2) <> DOM_SYMBOLIC) then
          partn:=string(expr2);
        else
          partn:=convToRPN2(expr2);
        end;
        if (partJ > 1) then 
          rpnStr:=rpnStr + " "; 
        end;
        rpnStr:=rpnStr + partn;
        if ((partJ > 1) or (parts == 1)) then
          rpnStr:=rpnStr + " " + oper;
        end;
      end;

      return(rpnStr);
    end;
#end 


convToRPN2(x^3); returns "x 3 ^"


///////////////

Running step by step convToRPN2(x^3);, for those who want to see the conversion of x^3 to RPN
more info on RPN
https://en.wikipedia.org/wiki/Reverse_Polish_notation

PHP Code:

expr1:=x^3;
rpnStr:="";
oper:="";
partn:="";
oper:=part(expr1,0); //returns "^"
parts:=part(expr1); //returns 2
partJ:=1;
expr2:=part(expr1,partJ); //returns x
partn:=string(expr2); //returns "x"
rpnStr:=rpnStr + partn; // returns "x"
partJ:=2;
expr2:=part(expr1,partJ); //returns 3
partn:=string(expr2); //returns "3"
rpnStr:=rpnStr + " "; //returns "x "
rpnStr:=rpnStr + partn; //returns "x 3"
rpnStr:=rpnStr + " " + oper; //returns "x 3 ^" 


Or in a list of steps, without comments to copy and paste them in the history view

PHP Code:

expr1:=x^3; rpnStr:=""; oper:=""; partn:=""; oper:=part(expr1,0); parts:=part(expr1); partJ:=1; expr2:=part(expr1,partJ); partn:=string(expr2); rpnStr:=rpnStr + partn; partJ:=2; expr2:=part(expr1,partJ); partn:=string(expr2); rpnStr:=rpnStr + " ";rpnStr:=rpnStr + partn; rpnStr:=rpnStr + " " + oper; 


returns

PHP Code:

[ x^3,"","","","^",2,1,x,"x","x",2,3,"3","x ","x 3","x 3 ^"]