How to make a function like eval ?

Hello,

I need a modified eval function. For example, I have in my workspace :

Nx = 3;
mystring = '1+2*Nx';
is_string = false; % treat it as matlab code
is_string2 = true; % treat it as text

I want to run the following lines :

if is_string, out = mystring,
else out = eval(mystring),
end
if is_string2, out2 = mystring,
else out2 = eval(mystring),
end

I am looking for a way to put this in a function :

Nx = 3;
mystring = '1+2*Nx'
is_string = false; % treat it as matlab code
is_string2 = true; % treat it as text
out = my_eval(mystring,is_string) % returns 7
out2 =my_eval(mystring,is_string2) % returns '1+2*Nx'

Anybody knows how to do this ?

Thanks

Answer 1

[dpb]

function out=my_eval(in,isStr)
  if isStr
    out=in;
  else
    out=evalin('caller',in);
  end

doc evalin % for details/limitations

Might also consider using function handles and, perhaps creating dynamically an anonymous function handle which is then evaluted...depends on the end use.

[Arnaud]

Thanks ! Obviously I should have looked at the end of the eval function to find this evalin function !

Answer 2

[Adam]

I would define as follows:

Nx = 3;
myFunc = @() 1 + 2*Nx

then

out = my_eval( myFunc, is_string )

would contain something like:

if is_string
    out = strrep( func2str( myFunc ), '@()', '' )
else
    out = myFunc();
end

[Arnaud]

Thanks but I'd rather not modify my string.