Harvey Abramson. A Prological Definition or HASL: a Purely Functional Language with Unification Based Conditional Binding Expressions. In Luís Moniz Pereira, António Porto, Luís Monteiro, Miguel Figueiras, editors, Logic Programming Workshop '83, Praia da Falésia, Algarve, Portugal, 26 June - 1 July, 1983, Proceedings. pages 7-39, Núcleo de Intelligência Artificial, Universidade Nova De Lisboa, Portugal, 1983. [doi]