Control flow within the eval function in Matlab

As @Daniel pointed out, the eval

script is called while it is not directly controlled by the outline for

. You may think that it is: continue

in eval

will move the program counter in the beginning of the code inside eval

, but not in the loop for

; this will of course fail as Matlab doesn't allow line jumping.

A continue

can be displayed directly inside the loop for

or while

. However, you can hack the code like this:

for ii=1:numel(listParam),
    eval(['if isnan(',listParam{ii},'), x=1; else, x=0; end']);
    if x
        continue;
    end
    disp(['The parameter ', listParam{ii}, ' is not a NaN.']);
end

      

        
        
        
      

    

Strange, x

appears on the script stack. However, this is far from good code. Never use this method.

Edit: about the "control" area eval

.

I'm not talking about variable scope / workspace eval

. Hints can be found in several docs such as this and this . In short, it eval

uses the "current" workspace.

However, I found the following interesting things:

• Executing continue
  
  directly ineval
  
  

  for ii = 1:2
      eval('continue')
      ii+10
  end
  
        
  
          
          
          
        
  
      

  It just fails as shown in the question. Error Error: A CONTINUE may only be used within a FOR or WHILE loop.
  
  , which means it cannot find any loop (loop ) continue
  
  inside .eval

for
  
  

• Calling a separate script in a loop for
  
  

  for ii = 1:2
      foo
      ii+10
  end
  
        
  
          
          
          
        
  
      

  and the script foo.m
  
  is

  ii
  continue
  
        
  
          
          
          
        
  
      

  First of all, foo.m
  
  Mlint gives a red line warning, which usually indicates an error that could stop the code from running by indicating that CONTINUE is only valid in a FOR or WHILE loop
  
  . But pressing F5 foo.m
  
  doesn't cause any problems - in fact, running one continue
  
  anywhere doesn't crash the code.

  Running the main script gives the output

  ii =
       1
  ii =
       2
  >> 
  
        
  
          
          
          
        
  
      

  .... so what is foo.m
  
  catching the loop for
  
  ?

• eval('foo')
  
  - I really don't understand Matlab

  for ii = 1:2
      eval('foo')
      ii+10
  end
  
        
  
          
          
          
        
  
      

  The result surprised me a little.

  ii =
       1
  ans =
      11
  ii =
       2
  ans =
      12
  >> 
  
        
  
          
          
          
        
  
      

Thought: eval

Runs code in an independent control flow, but shares its workspace with the current one. It is (something, but not quite) like an isolated world model in which (here in Matlab) different pieces of code can interact with the same set of variables, but cannot interact with each other in the sense of control flow.

Unfortunately, I have not been able to find any existing resources as a link to prove this idea.

This does not change my mind: try to avoid using it anyway eval

.