Hello,

I think there is some kind of misunderstanding here. There is a mistake to define variables in this way and both definitions of variables are incorrect (result and result2). You can see that by hovering the mouse over them. You should define variables like this:


line(k:0,for(i,range(1,length(X)),line(k:k+1,el(result,k):el(X,i)*el(Y,i),2,1)),result,3,1)

and


for(i,range(1,length(X)),el(result2,i):el(X,i)+el(Y,i))

Additional result:= and result2:= in front of these constructions are making a mess.
Regarding the first one here are the pictures. Lines are like vector elements.





In the second one the for loop is executing but the assignment is incorrect, therefore the syntax error.



Regards,
Radovan

Edited by user 27 May 2012 15:21:06(UTC)  | Reason: Not specified

Hi,

I tried to understand what happened in the example. My current guess is:

The operations

k:0

result:line(for(i;range(1;length(X));line(k:k+1;el(result;k):el(X;i)*el(Y;i);2;1));result;2;1)

use result to store the line structure of expressions symbolically. Whenever evaluation is requested by the = operator, then the stored expression is evaluated using the current value of all variables involved in the definition. Assignment to "result" just changes the definition.

If the : Operator is meant to assign the evaluated result of some expression, then eval() has to be used. Any later change of variables used in the expression do not affect the content the formerly evaluated result.

In both cases nothing seems to be wrong with using the same variable name as return value for the line operator and as target for the expression assignment. Replacing result by result1 inside the expression has no effect on the behavior (at least in this small example). This might be due to that the line operator shields parameter arguments in function definitions and return values from global name space

result:eval(line(k:1;for(i;range(1;length(X));line(k:k+1;el(result;k):el(X;i)*el(Y;i);2;1));result;3;1))

If you try to assign the for operator to a variable, this fails.

result2:for(i;range(1;length(X));el(result1;i):el(X;i)+el(Y;i))

result2 is undefined, result1 contains the expected vector.

Based on that guess I would propose the following:

• More specific error message (e.g. "Assignment of for statement is ignored" ) in the result2 case.
  
• Disabling of assignment to elements of line structures unless it is meant to edit or automatically generate them. In that case assignment of assignment expressions like el(result;1):k:2 or similar statements should be possible ;-)
  

Martin