The issue is raised in http://www.mathworks.com/matlabcentral/answers/7685-m-function-in-a-m-script
Or a previous discussion http://www.mathworks.com/matlabcentral/newsreader/view_thread/298837
Vote if you want Mathworks NOT to add this feature.
If you like this feature, please vote on the other post. http://www.mathworks.com/matlabcentral/answers/7690-please-vote-if-you-want-to-have-m-function-in-m-script
If you DON't CARE, you can also vote. http://www.mathworks.com/matlabcentral/answers/7699-please-vote-if-you-don-t-care-to-have-m-function-in-m-script
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+1: Better spend the time to improve the GUI objects - continuous slider callbacks, stable UITREE with supported context menu, sortable UITAB, let FIGURE(FigH) move the keyboard focus to the figure as claimed in the documentation (is this solved in 2011a?! It did not work from 5.3 to 2009a...), ComboBox (editable popup menu), stable GETFRAME (no need for PAUSE(0.02) to wait for drawing of Java objects), fix problems with OpenGL renderer (2% of the 2D plots with enabled Box miss the upper border), ...
The only time I use scripts is as temporary scratch-pads, pasting in code from questions in order to see what it does or to debug it. And all that does is save me the trouble of adding a "function" line at the top.
The Programming Theory part of me says that Mathworks should not do this: that instead they should work on allowing MATLAB to be "reflective" like Scheme; see here for more information on Reflection. (Disclaimer: I have met the inventor of Reflection in programming languages, and some of my friends worked directly with him in extending the ideas.)