Sometimes, Rainfall Accumulates: Talk-Alouds with Novice Functional Programmers

When functional programming is used in studies of the Rainfall problem in CS1, most students seem to perform fairly well. A handful of students, however, still struggle, though with different surface-level errors than those reported for students programming imperatively. Prior research suggests that novice programmers tackle problems by refining a high-level program schema that they have seen for a similar problem. Functional-programming students, however, have often seen multiple schemas that would apply to Rainfall. How do novices navigate these choices? This paper presents results from a talk-aloud study in which novice functional programmers worked on Rainfall. We describe the criteria that drove students to select, and sometimes switch, their high-level program schema, as well as points where students realized that their chosen schema was not working. Our main contribution lies in our observations of how novice programmers approach a multi-task planning problem in the face of multiple viable schemas.