Evaluating the Tracing of Recursion in the Substitution Notional Machine

Preston Tunnell Wilson, Kathi Fisler, Shriram Krishnamurthi

ACM Technical Symposium on Computer Science Education, 2018


We evaluate a notional machine for recursion based on algebraic substitution. To do this, we decompose recursion into a progression of function call patterns, parameter name reuse, and data structure complexity. At each stage, we test students’ ability to trace programs using substitution. We evaluate the correctness of their traces along multiple dimensions, finding that students generally do well, and also observe shortcuts and identify misconceptions. For comparison, we also have students trace two problems using a traditional, imperative notional machine. Even though the substitution model is unwieldy to use with compound data, students still perform better with it than with the traditional notional machine.



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