Evaluating Haskell expressions in a tutoring environment

TL;DR

This paper introduces a prototype tool for stepwise evaluation of Haskell expressions aimed at educational use, enabling students to perform and receive feedback on expression evaluation steps to enhance understanding of functional programming concepts.

Contribution

It presents a novel interactive evaluator supporting multiple strategies, with feedback and easy customization for instructors, tailored for teaching Haskell evaluation.

Findings

Students improved understanding of evaluation steps

The tool provided useful feedback for learners

Preliminary survey results indicate positive educational impact

Abstract

A number of introductory textbooks for Haskell use calculations right from the start to give the reader insight into the evaluation of expressions and the behavior of functional programs. Many programming concepts that are important in the functional programming paradigm, such as recursion, higher-order functions, pattern-matching, and lazy evaluation, can be partially explained by showing a stepwise computation. A student gets a better understanding of these concepts if she performs these evaluation steps herself. Tool support for experimenting with the evaluation of Haskell expressions is currently lacking. In this paper we present a prototype implementation of a stepwise evaluator for Haskell expressions that supports multiple evaluation strategies, specifically targeted at education. Besides performing evaluation steps the tool also diagnoses steps that are submitted by a student, and provides feedback. Instructors can add or change function definitions without knowledge of the tool's internal implementation. We discuss some preliminary results of a small survey about the tool.