To exercise the entire if/else block, put the test in named file and execute it, with BLANK set to BLANK(mfilename) . BLANK.m would have a persistent variable; if the persistent variable is empty, then set the variable to something, evalc() the mfile whose name was passed in, fwrite(1) the string returned by evalc, and return false . If the persistent variable is not empty, then set it empty and return true .
The mfile would start executing, would call BLANK, which would set its internal flag and recurse the mfile. The second call to BLANK would detect the flag being set and would return true (no recursion), so that recursed call would display the "I Love " and then exit the recursion. Now back at the first level, BLANK has captured the "I Love " and displays it suppressing the newline, and returns false, so the non-recursed mfile executes the else, printing out the "MATLAB" and exiting.