CYNTHIA is a novel editor for the functional programming language ML in which each function definition is represented as the proof of a simple specification. Users of CYNTHIA edit programs by applying sequences of high-level editing commands to existing programs. These commands make changes to the proof representation from which a new program is then extracted. The use of proofs is a sound framework for analysing ML programs and giving useful feedback about errors. Amongst the properties analysed within CY NTHIA at present is termination. CYNTHIA has been successfully used in the teaching of ML in two courses at Napier University, Scotland. CYNTHIA is a convincing, real-world application of the proofs-as-programs idea