An experimental language from the University of Nijmegen and University of East Anglia, based on graph rewriting and useful as an intermediate language. Lean is descended from Dactl0.

Clean is a subset of Lean.

["Towards an Intermediate Language Based on Graph Rewriting", H.P. Barendregt et al in PARLE: Parallel Architectures and Languages Europe, G. Goos ed, LNCS 259, Springer 1987, pp.159-175].