  In recent years we have explored using Haskell alongside a traditional
mathematical formalism in our large-enrolment university course on topics
including logic and formal languages, aiming to offer our students a
programming perspective on these mathematical topics. We have found it possible
to offer almost all formative and summative assessment through an interactive
learning platform, using Haskell as a lingua franca for digital exercises
across our broad syllabus. One of the hardest exercises to convert into this
format are traditional written proofs conveying constructive arguments. In this
paper we reflect on the digitisation of this kind of exercise. We share many
examples of Haskell exercises designed to target similar skills to written
proof exercises across topics in propositional logic and formal languages,
discussing various aspects of the design of such exercises. We also catalogue a
sample of student responses to such exercises. This discussion contributes to
our broader exploration of programming problems as a flexible digital medium
for learning and assessment.
