The Sifflet visual functional programming language and aid to understanding recursive functions (http://mypage.iu.edu/~gdweber/software/sifflet/home.html)
#56Exporting redefinitions of built-in functions
After a user defines a function named 'length' and exports to Python, there is no length function in the exported file.
Observed September 20, 2013, at CCSC:MW presentation.
Diagnosis: length is a built-in Sifflet function, so included in sifflet.py (the supporting library for Python), and therefore not included in length.py (the exported file).
What should have happened: either prohibit redefining built-in functions, or allow it (with a warning), but if the new definition differs from the old, it should then be exported.